The

Recombined
Reference
A comprehensive guide to
the recombination of milk
and milk products.
70
Years of
Recombination
Expertise
A practical guide to Recombined Milk.

Important Disclaimer
Fonterra Co-operative Group Limited and its The information and/or opinions contained in this
subsidiaries, affiliates, agents, suppliers and distributors manual are current as of the date of issue of this manual
(collectively ‘Fonterra’) make no representations or and are based on information and facts known to
warranties of any kind with respect to the information Fonterra on such date of issue. The information and/or
and/or opinions contained in this manual including, but opinions contained in this manual may be changed at
not limited to, any representation or warranty as to the any time without notice and Fonterra does not assume
accuracy, adequacy or completeness of such information any obligation to review or update such information
and/or opinions or that such information and/or opinions and/or opinions.
are suitable for your intended use.
Acknowledgements
This is the fourth edition of this reference. With expanded
and updated content from referenced sources, our
experimental results, and generations of experience
within Fonterra, we are delighted to share over 70 years
of recombining expertise with you.

We are indebted to the following authors:

Nick Robinson John Ramsay Lisa Rutherford

David Oldfield Taryn Kramer Andrew Legg
Ros Robertson Enoch Hui Shaun Thompson
Vikas Gaur Elise Van Ginkel Quinn McKay
Paul Andrewes Jonathan Depree Simon Gilmour
Maria Ferrua David Pearce

We would also like to acknowledge the contributions of:

Grace Cabuay Ben Somerton

Jos Schalk Olivia Lawrence

The authors of the previous editions:

David Newstead Brent Vautier

Susan Reelick Bing Soo
2 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022
Contents

Glossary p.6
1. Introduction p.10
2. Ingredients p.14
3. Recombining Milk p.28
4. Recombined Milk – Normal Concentration p.82
5. Recombined Milk – Concentrated p.112
6. Creams p.136
7. Formulated Dairy Beverages p.154
8. Cultured Products p.186
9. Cheese Milk Extension and Recombined Cheese p.206
10. Nutrition p.224

© FONTERRA CO-OPERATIVE GROUP LIMITED 2022 3

Glossary

Abbreviations and acronyms

Adenosine triphosphate ATP Matrix-assisted laser desorption/ionisation
Aerobic plate count APC time-of-flight mass spectroscopy MALDI-ToF
American Dairy Products Institute ADPI Medium heat MH
American standard AS Microgram µg
Anhydrous milk fat AMF Micrometre µm
Aanisidine value AV Milligram mg
Bag in box BIB Millilitre mL
British Standard BS Millimoles mmol
Buttermilk powder BMP Milk protein concentrate MPC
Carboxymethyl cellulose CMC Milk-fat-globule membrane MFGM
Centipoise (equivalent to 1 mPa.s) cP Milk-solids-not-fat MSNF
Cheese milk extension CME Minute(s) min
Cold-water soluble CWS Modified atmosphere packaging MAP
Colony-forming units cfu or CFU Monosodium dihydrogen orthophosphate MSP
Digestible indispensable amino acid score DIAAS Non-communicable diseases NCD
Direct steam injection DSI Parts per million ppm
Disodium monohydrogen orthophosphate DSP Peroxide value PV
Docosahexaenoic acid Polyethylene terephthalate PET
(an omega-3 fatty acid) DHA Polydimethylsiloxane PDMS
Extended shelf life ESL Polyunsaturated fatty acid PUFA
Free Available Chlorine FAC Potassium hydroxide (alkali) KOH
Fat-filled milk powder FFMP Ready to drink RTD
Fermented milk drink FMD Reactive nitrogen species RNS
Food Standards Australia New Zealand FSANZ Reactive oxygen species ROS
Free fatty acids FFA Recombined concentrated milk RCM
Fresh frozen milk fat for recombining FFMR Recombined evaporated milk REM
Frozen whole milk concentrate FWMC Recombined sweetened condensed milk RSCM
Heat coagulation time HCT Recommended daily intake RDI
Heat-resistant mesophilic spores HRMS Residual oxygen RO
High heat HH Rotor stator mixer RSM
High heat, heat stable HHHS Second(s) s
High methyl ester HM Skim milk powder SMP
High methoxyl HM Skim milk solids SMS
High total solids recombined cheese HTSRC Sodium hydroxide NaOH
High-shear mixer HSM Thermophilic acidophilic bacteria TAB
Highly heat-resistant spore HHRS Thiobarbituric acid reactive substances TBARS
Hour(s) h Titratable acidity TA
Hydrogen chloride (acid) HCl Total milk protein TMP
Intermediate bulk containers IBC Total solids TS
International Dairy Federation IDF Ultra-high temperature UHT
Litre(s) L Weight/weight w/w
Low heat LH Whey protein concentrate WPC
Low methyl ester LM Whey protein isolate WPI
Malt extract agar MEA Whey protein nitrogen index WPNI
Whole milk powder WMP

4 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

Glossary

Useful terms
A-tank – An aseptic tank, holding sterilised product Flocculation – a process whereby small particles in
before filling into packaging. Provides a buffer between suspension are caused to aggregate, giving large clusters
the steriliser and packaging. (flocs) that are much more easily separated than the
original particles.
Coalescence – process by which two or more droplets
fused to form a bigger droplet. Functional MPC – a milk protein concentrate that
has superior functional properties compared to
D value – a decimal reduction time, death rate of micro-
standard MPCs.
organisms. The time required at a specified temperature,
and under specified conditions, for a ten-fold (1 log10 Functional WPC – a whey protein concentrate that can
or 90%) reduction in the numbers of a specified be used at high addition levels while maintaining a low
organism. Factors such as food type, pH, presence of viscosity and texture.
preservatives and microorganism stage of growth can
Gelation – a beverage defect occurring during shelf life.
affect the D value.
Appearance of a soft semi-solid gel.
F0 – relevant for moist heat sterilisation processes and
(Maillard) Browning – reaction between milk protein and
represents the number of minutes required to kill a
the milk sugar lactose that results in the formation of
known population of microorganisms in a given food
compounds that affect the colour and flavour.
under specified conditions. F0 is also referred to as the
equivalent exposure time at 121.1°C for a process; when Powder addition – manual tipping of dry powders over
F0 is used without a subscript indicating temperature, the liquid line in a process tank.
121.1°C is assumed.
Powder induction – the incorporation of dry powders into
Example: as the F0 value is the heat treatment time a liquid facilitated using a machine specifically designed
relative to 121.1°C, an F0 of 3 is a heat treatment that to aid the dispersion and efficient wettability of the
is equivalent to 3 mins at 121.1°C. The z values can be powder.
used to determine an F0 equivalence when temperatures
Sedimentation – a beverage defect occurring during
> 121.1°C are used, using the equation F0 = t/60 x
shelf life. Appearance of a layer at the bottom of the
10^(T-121.1/z) (z is usually considered to be 10°C).
packaging, typically very shortly after manufacturing.
D121.1°C values can also be used to estimate the
achieved log reduction at a given F0; if F0 is 3 min, and Sterilisation – strictly, “sterilisation” means to remove, kill
D121.1°C is 0.25 min, then the log reduction is 3/0.25 = 12. or deactivate all forms of life. In this manual, as in many
areas of food processing, the term is used more loosely
In the canning industry, the F0 value is usually set at 12-D
to mean “aseptically processed to achieve acceptable
values to give a theoretical 12-log cycle reduction of
microbiological control within the stated shelf life”.
Clostridium botulinum (the most relevant spore-former in
this context). Therefore, if there were 10,000 C. botulinum (1) “Commercial sterility means the absence of
spores in a can of food and a 12-D process was applied, microorganisms capable of growing in the food at
the C. botulinum spore count would be reduced to a normal non-refrigerated conditions at which the food
theoretical 10-8 living spores per can [i.e. one viable spore is likely to be held during manufacture, distribution and
per 108 (one hundred million cans) of product]. storage.” [Ref: Codex Alimentarius Commission (WHO/
FAO) CAC/RCP 40-1993].

6 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

(2) The EU defines the heat treatment necessary to
achieving commercial sterility as “UHT treatment is
achieved by a treatment: (i) involving a continuous flow
of heat at a high temperature for a short time (not
less than 135°C in combination with a suitable holding
time) such that there are no viable microorganisms or
spores capable of growing in the treated product when
kept in an aseptic container at ambient temperature,
and (ii) sufficient to ensure that the products remain
microbiologically stable after incubating for 15 days at
30°C in closed containers or for seven days at 55°C in
closed containers or after any method demonstrating
that the appropriate heat treatment has been applied.”
[Ref: Commission Regulation (EC) No. 1662/2006
(amending Regulation (EC) No. 853/2004)].
Water activity – the partial vapour pressure of water in
a solution divided by the standard state partial vapour
pressure of water, measured at the same temperature.
In the field of food, a plain language definition is “water
not sufficiently bound to food molecules that it can form
a vapour”.
Z value – temperature coefficient; effect of temperature
on the D value. The z value is the increase (or decrease) in
temperature required to impact the D value by a factor
of 10. The z value gives an indication of the relative
impact of different temperatures on a microorganism,
with smaller z values indicating greater sensitivity
to increasing heat at the temperature range under
consideration.

7
1.
The Recombined
Reference
A comprehensive guide to
the recombination of milk and
milk products.

8 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

9
1

Introduction
1.
Introduction

1.1 Recombining milk can provide dairy-based nutrition

where fresh milk is not a practical option. This manual
Overview provides a comprehensive insight into the basic principles
and processes you need to master to manufacture
Recombination is a process whereby milk that has been recombined milk products successfully. It is intended
dried into a powder form is then reconstituted to return as a practical guide and will be helpful as a reference
it to liquid form. It has early origins, with Marco Polo during recombination.
mentioning a similar process in 1295 AD. Recombination
Fonterra is a co-operative owned by 10,000 New Zealand
has been extensively used in the South East Asia region
to produce various forms of recombined milk. With farming families. We have created this reference for our
the further development of recombined milk product customers and other parties in the dairy industry. This
technology through the 1970s and 1980s (and currently manual is based on scientific sources, our unpublished
ongoing), it is possible to create all traditional dairy research and the wealth of experience and expertise we
products by recombining dried ingredients. have in dairying.

10 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

11
1

Introduction
2.
Ingredients
This chapter provides an introduction to
the main recombined milk and milk product
ingredients, including their composition,
quality requirements, grades, storage,
handling and sampling.

12 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

13
2

Ingredients
 Table 2.1:
Typical gross composition of ingredients for recombined milk and related dairy products (% m/m).

Fat Protein1 Lactose Minerals Water

(as ash)
Whole milk powder (WMP)2 26.8 25.0 39.1 5.8 3.3
Skim milk powder (SMP) 0.8 33.4 54.1 7.9 3.8
Skim milk/vegetable fat blend in powdered form (FFMP) 3
26.0 24.0 39.0 6.0 5.0
Cream powder 54.9 15.6 23.3 3.5 2.7
Buttermilk powder (BMP) 8.0 31.0 50.0 7.2 3.8
Frozen whole milk concentrate (FWMC) 5
13.0 13.3 17.6 3.1 53.0
Anhydrous milk fat (AMF) 5
99.9 – – – 0.1
Frozen cream 5
42.0 2.0 2.0 0.6 53.0
Milk protein concentrate 70 (MPC70) 6
1.2 69.9 16.8 7.4 4.7
Whey protein powder7 0.8 15.1 71.6 7.9 4.6
Whey protein concentrate 80 (WPC80)7 10.0 79.5 10.0 4.0 6.0
Caseinate8 2.0 88.0 1.0 – 8.0

1. The international standard for milk powders (Codex, 1999) gives the minimum protein content as 34% of the non-fat milk solids.
2. A range of fat contents is available, most commonly a nominal 26% fat product (shown here) and a 28% fat product.
3. The international standard (Codex, 2006) gives the minimum protein content as 34% of the non-fat solids; the minimum fat content is as
shown; the moisture level shown is the allowed maximum; minerals and lactose are typical values. The same Codex standard defines reduced
fat blends as those with a fat level > 1.5% and < 26.0%. For the purposes of this manual Fat Filled Milk Powder shall be referred to as FFMP.
4. FWMC is a concentrated source of dairy solids produced from milk. The concentrate is frozen and stored frozen until used.
5. A range of fat contents is available for Frozen Cream, typically ≥ 18% (“single” or “light”) or ≥ 36% (“double”, “heavy” or “whipping”), made
from bovine whole milk passing through a cream separator and snap freezing. The Codex standard for cream (Codex, 1976) describes a
minimum fat content of 10% w/w of the fluid cream. The values noted for frozen cream are typical of heavy cream after snap freezing.
AMF can also be manufactured as a frozen ingredient and stored frozen. AMF as a frozen ingredient can also be called Fresh Frozen Milk
fat for Recombining (FFMR).
6. A range of protein contents is available, typically 70, 80 or 85%, made from passing bovine skim milk through filtration processes, to obtain
a dry product of ≥ 40% protein by weight. The 70% protein ingredient is given here as a typical example.
7. A range of protein contents is available, typically 34% or 80%, made by the removal of non-protein constituents from whey to obtain a dry
product containing ≥ 25% protein. The 80% protein ingredient is given here as a typical example. The gross composition numbers add to >
100% as the ADPI standard describes the protein level as the minimum required; the moisture and fat levels are the maxima allowed; the
lactose and ash levels are typical. Values provided are typical. ADPI has a “Dry Whey” product standard that sets a minimum protein level
of 11.0%, and maximum ash levels of 8.5% for sweet whey powder and 15.0% for acid whey powder.
8. A range of caseinates is available, typically as a sodium or calcium caseinate ingredient. These are made from the precipitation of casein
proteins from bovine skim milk and redissolution through pH adjustment to obtain a dry product. The protein content described by the Codex
standard (Codex, 1995) is given here as a minimum; moisture and fat are allowed maxima and lactose is typical. There is also a maximum pH
of 8.0 in the standard.

14 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

 2
2.
Ingredients

Ingredients
2.1 2.1.1
Dairy ingredients Gross composition of ingredients
The composition of ingredients specific to particular
Fluid whole milk can be manufactured into many dairy applications is covered in later chapters.
ingredients. Those most commonly used in recombined
applications are shaded green in Figure 2.1.

Figure 2.1:
The main ingredients derived from milk. Ingredients most commonly used in recombined applications are shaded green.

Whole Milk
Powder

Concentrated Cheese Powder

Buttermilk Whole Milk
Powder
Processed Cheese
Buttermilk
Ch
r
tte

ee
Bu

se

Fluid
Whole Milk
Lactalbumin
Whey Protein
Hydrolysate
Cr

Cream Cheese
y
he
ea

Whey Protein
W
m

Sour Cream Isolate 90

Cream Powder
Whey Protein
Fluid Concentrate 80
Anhydrous
Milk Fat Skim Milk
Whey Powder
Frozen Cream
Casein
Skim Milk Powder Lactose
TMP

Milk Protein Caseinate

Concentrate

15
2. EXPERT TIP:
For manufacturers of milk-based

Ingredients
drinks containing vegetable oils,
FFMP provides benefits of
convenience and simple handling,
as the protein and fat are already
combined into a stable emulsion.

2.1.2 Each formulation has unique product

Ingredients for different recombined characteristics
milk formulations The ingredients in Table 2.2 can be combined to make
products that are similar, but not identical, in
The simplest way to make a recombined milk is to composition and final properties. Flavour targets, long-
use whole milk powder (WMP). With this method term product stability and processing operations should
an emulsifier is optional, depending on the required be considered. Details to support this are provided in
longer-term stability. later chapters. Market-specific regulations, although
outside the scope of this manual, are important also.
Table 2.2 shows other formulations with
the following benefits: The product differences are caused by the ingredient
manufacturing process. The various ingredients contain
Option 1: Heat stability in recombined
different amounts of naturally-occurring surfactant
evaporated milk products.
material derived from the natural milk-fat-globule
Option 2: Formulation flexibility. membrane. This membrane material gives some end
products very desirable functional properties (Newstead,
Option 3: No ingredient drying step.
1999) that are detailed in Chapter 3.
Properties attributed to the natural fat-globule-
membrane material include:
Table 2.2:
Possible ingredients for recombined milk and • Nutritional benefits of membrane components
milk-based formulations.
(Gallier et al., 2018).
• Reduced fouling in ultra-high temperature (UHT)
1. WMP (emulsifier)
plants (Srichantra et al., 2018).
2. WMP, (SMP or cream powder) (emulsifier) • Increased heat stability of recombined evaporated
3. SMP, AMF, BMP emulsifier milk (REM) (Singh & Tokley, 1990).
4. SMP, AMF emulsifier
5. FWMC (emulsifier) 2.1.3
6. FFMP (emulsifier)
General quality requirements
7. SMP, vegetable oil emulsifier
for dairy ingredients
( ) Indicates an optional ingredient. The recommended quality limits for powders and milk
fat are given in Table 2.3. FWMC does not have an
international standard, and for protein powders, the
lack of definite standards (Meena et al., 2017) meant
that no reliable data on international quality limits could
be found.
The corresponding typical composition data is in Table 2.1.

16 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

 2
EXPERT TIP:
Unsalted butter is not
recommended for recombining.
Although unsalted butter can be

Ingredients
Ingredients
used as a source of milk fat, it is
not recommended here. It requires
frozen transport and storage, as
well as special care during melting,
to prevent bacterial growth.

Table 2.3:
Recommended quality limits for powders and milk fat.

Powders
Codex Alimentarius recommendations from Codex 1999.

Property SMP WMP BMP Cream powder Method

Milk fat not more ≥ 26, < 42 > 1.5, < 26 not less IDF Standard 9C: 1987
(% w/w) than 1.5 than 42
Water (% w/w) (maximum) 5 5 5 5 IDF Standard 26A: 1993
Protein in milk solids-not-fat 34 34 34 34 IDF Standard 20-1/
(% w/w) (minimum) ISO 8968-1 (2001)
Titratable acidity 18.0 18.0 18.0 18.0 IDF Standards 86:
(mL 0.1 N NaOH/10 g 1981 and 81: 1981;
solids-not-fat) (maximum) Codex Standard 234-1999
Scorched particles Disc B Disc B Disc B Disc B IDF Standard 107A: 1995;
(maximum) Codex Standard 234-1999
Insolubility index 1 mL 1 mL 1 mL 1 mL IDF Standard 129A: 1988;
(maximum) Codex Standard 234-1999

Additional recommendations
Aerobic plate count < 2 × 104 cfu/g < 2 × 104 cfu/g < 2 × 104 cfu/g < 2 × 104 cfu/g IDF Standard 100B:
(mesophilic) 1991 and ISO 4833:2003
Coliforms Absent in 1 g Absent in 1 g Absent in 1 g Absent in 1 g ISO 4832: 2006
Flavour and odour clean clean clean clean Reconstituted at
(reconstituted) 20°C–25°C. IDF
Standard 99-2: 2009

Anhydrous milk fat

IDF Standard 68A: 1977

Property SMP
Milk fat (minimum) 99.8% (w/w)

Water (maximum) 0.1% (w/w)

Free fatty acid as oleic acid (maximum) 0.3% (w/w)
Copper (maximum) 0.05 mg/kg
Iron (maximum) 0.2 mg/kg
Peroxide value (maximum) 0.2 milli-equivalents of O2/kg
Coliforms Absent in 1 g
Taste and colour Clean and bland at 20°C–25°C

17
 EXPERT TIP:
Do not use the whey protein nitrogen
index (WPNI) scale when buying
whole milk powder (WMP).
The WPNI is a heat classification
system that defines grades of skim
milk powder (SMP), but it does
not apply to WMP. Working closely
with suppliers is the best way to
ensure premium WMPs have the
appropriate-quality specifications.

18 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

 2
2. EXPERT TIP:
Over-interpreting WPNI for

Ingredients
SMP properties
Apart from bread baking (WPNI

Ingredients
< 1.5) and making semi-hard cheese
(WPNI > 6.0), most applications
do not require SMP with a specific
WPNI range. That is why the WPNI
should only be used as an indication
of the heat treatment applied to the
milk and not over-interpreted as a
measure of the SMP’s properties.

Premium grades of WMP – Grades of SMP – the WPNI system

tailored to application SMP is classified according to the amount of heat
Customers’ evolving needs have led to new areas of treatment applied to the milk during its manufacture.
functional performance for WMP. In the past, natural The bread-baking industry was one of the first to need
variations in milk as a raw material were generally this classification. They required SMP with a high heat
accepted by consumers. However, growth in products – treatment as a nutritional supplement in the bread and
such as long-life UHT milks, cultured foods and cultured to create the best texture. This led to the whey protein
drinks – has raised consumer expectations, leading to nitrogen index (WPNI) test.
new specifications and consistency levels. The resulting
The WPNI is an indirect estimate of the heat treatment
benefits include:
applied. Whey proteins in milk are relatively heat
• Good flavour – especially creamy flavour and sensitive (casein protein is not), so the amount of
texture, consistently delivered. whey protein denaturation indicates the level of heat
• Processability – such as low fouling in a UHT plant. treatment. The WPNI value is defined as the amount, in
mg, of native whey protein nitrogen remaining in 1 g of
• Long-term product stability – such as the absence
the SMP (ADMI, 1971).
of sediment or gelling in UHT milks.
• Instant reconstitution – drawing on technologies The classification scale gives the following three ranges.
to ‘instantise’ the WMP during manufacture.

Buying the right premium WMP Table 2.4:

Classification scale for WPNI.
During WMP manufacture, priority is given to applying
a level of heat treatment that allows the milk to develop
Class Whey protein nitrogen index
antioxidant compounds. These inhibit flavour taint
development to prolong the final WMP’s shelf life. There High heat Not > 1.5 mg/g
is, therefore, little relevance in trying to define the heat Medium heat 1.5–6.0 mg/g
treatment applied to WMP in terms of the WPNI scale
for SMP.
Low heat Not < 6.0 mg/g

However, different levels of heat treatment during

ingredient manufacture can affect the functional Classes of SMP recommended for particular products are
performance benefits noted above. The work of identified in later sections of this manual. For example,
Srichantra et al. (2018) on the fouling effects of pre-heat Chapter 9, section 9.6, explains the importance of using
treatment of whole milk provides a relevant example. low-heat SMP for making cheeses, including recombined
semi-hard and panela cheeses. This is because whey
As indicated in Robinson et al. (2019), various other proteins that have been exposed to high heat decrease
historical methods have been misappropriated or rennet activity. For other applications in which the pre-
misused to prove a WMP’s fitness for purpose. It is heat treatment used in powder manufacture may be
therefore advisable to work closely with suppliers to critical, the WPNI scale is not always useful. Chapter 5,
ensure that premium WMP specifications include the section 5.3, on recombined sweetened condensed milk
appropriate-quality measures. (RSCM) explains this further.

19
2. EXPERT TIP:
Regularly check the water for typical

Ingredients
aroma and taste at the point of use.
This ensures there are no changes
in water source or water treatment
that could taint the recombined
milk product.

2.2
Water
The water used in a recombined milk product Regularly check the water for:
must be fit for drinking, or ‘potable’.
Bacterial spores
In general: Because spore contamination of product is possible
• The total hardness (calcium carbonate equivalent) from water sources. Relevant indicator tests include
should not exceed 100 parts per million (ppm). aerobic thermophilic spores (as these spores may be able
• The total dissolved solids should be < 500 ppm (NZ to withstand UHT treatment) and aerobic plate count
Ministry of Health, 2018) and preferably < 350 ppm (APC) as a general indicator of microbiological quality.
(EPA, 2020).
Pseudomonas
The recommended water purification methods are: Because it can form highly heat-stable enzymes
• Reverse osmosis for all chemical impurities. (proteases and lipases), tolerate high levels of chlorine
• Sodium ion exchange for calcium and in treated water systems and form biofilms. These
magnesium hardness. factors can produce heat-stable enzymes that
withstand UHT treatment, affecting end product
storage life and quality.

20 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

 2

Ingredients
EXPERT TIP:
Regularly check water for
spores and Pseudomonas.
The water should be regularly
checked for these micro-
organisms. Although chlorination
is effective against vegetative
bacteria, it has little effect on
spores or Pseudomonas (chlorine
resistant to up to 5–7 ppm FAC).

21
2.
Ingredients

2.3 Avoiding light exposure for milk fat

Storing, handling and Milk fat and powders containing milk fat should not
be exposed to light, as it rapidly increases the rate
sampling dairy ingredients of oxidative flavour formation. During recombining
operations, milk powder in the inner plastic bag liner,
stripped of the paper outer, must not be exposed to
2.3.1 light for extended periods.
Storing and handling dairy ingredients
Using ingredients in rotation
Milk powder and AMF All dairy ingredients should be used in rotation, preferably
SMP, WMP, BMP, cream powders, MPC, WPC and within the following periods after manufacture.
caseinates are normally supplied in multi-wall bags
with plastic liners. These should be stored in an odour-
free ventilated space with low humidity, avoiding Table 2.5:
direct contact with the walls or floors. Maintaining the Recommended maximum shelf life of ingredients.
humidity below 65% increases the shelf life.
AMF is supplied in lacquered steel drums. These AMF 12 months*
should be stored in cool, dry conditions. Lower storage
BMP 12 months
temperatures will increase shelf life by reducing
oxidation rates. Caseinate 24 months

Cream powder 9 months*

Bags of milk powder, drums of AMF and shipping
containers of any product should not be exposed to Frozen cream 18 months at -10°C to -25°C
the sun for long periods. FWMC 18 months at -18°C or below

Reduced oxygen containers for WMP, MPC 24 months

cream powders and AMF SMP 24 months

WMP and cream powders should be supplied in bags WMP 18 months*

with a reduced-oxygen atmosphere (flushed with WPC 24 months
nitrogen or a suitable gas mixture). AMF should be
supplied in nitrogen-flushed drums. After a bag or drum * Provided the low-oxygen packaging remains intact.
seal has been broken and air allowed in, the contained
product should not be stored for an extended period.

FWMC and frozen cream

temperature control
FMWC must be stored and transported at -18°C or
below, as higher temperatures can reduce shelf life and
solubility. Frozen cream should be stored frozen at -10
to -25°C to maintain its shelf life.

22 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

 2
EXPERT TIP:
Software for sampling design
Software applications that help
with sampling design details are

Ingredients
available in a package called ‘nz codex’
(Govinda, 2019). It covers topics such
as sampling plan design, batch size
effect, repeat testing, resampling and
lot heterogeneity. Using these as a
first approach is strongly encouraged,
because the alternative – random
sampling – often generates data
that does not represent the real risks
to consumers.

2.3.2 2.3.3
Sampling dairy ingredients Environmental monitoring
The main purpose of sampling ingredients is to ensure A comprehensive environmental pathogen monitoring
the customer receives product of the required quality and control programme should be operated in the plant.
and safety. In keeping with the Codex procedural Regular monitoring of the manufacturing environment
manual ((CAC/GL 83-2013) (GL 83)), it is reasonable for Salmonella and Listeria are key parts of such a
to expect that any sampling procedures conducted by programme. In the case of infant formula manufacture,
a customer are fair and valid when testing ingredients Cronobacter spp. should be additionally monitored. It
for compliance with a Codex standard. The manual is recommended that the sampling plan comprise a
acknowledges that financial resources are finite, and 3-D view of the plant and not just focus on floors, and
100% sampling is prohibitive and impractical, or may be pathogen monitoring and cleaning should take greater
excessive for most situations. priority in areas that have a closer vicinity to product and
product-contact surfaces.
Statistical sampling – the practical approach
The general microbial hygiene of the plant should
Whether the sampling is to screen for acceptable quality be monitored also. For example, swabs taken from
or resolve a quality problem, the practical approach is walls, ledges, floors and processing equipment for
based on probability. Although not every kilogram of APC, Enterobacteriaceae and yeasts and moulds, and
ingredient is inspected, the risks can be calculated by air-exposure plates for these microorganisms are
applying statistical techniques. useful tools for monitoring general plant hygiene and
The formalities and definitions of statistical techniques controlling air quality.
are covered elsewhere (Govinda, 2019) and no one
design fits all situations. Recombining practitioners
should take an approach that is anchored in science-
based industry practice.

23
References

1. ADMI (1971). Standards for Grades of Dry Milks 9. Environmental Protection Agency (EPA), USA
Including Methods of Analysis. American Dry Milk (2020). Retrieved from https://www.epa.gov/sdwa/
Institute Inc., Chicago, Illinois, USA. secondary-drinking-water-standards-guidance-
nuisance-chemicals. Total hardness has a guideline
2. ADPI (1971). Concentrated Milk Proteins Standard,
value for aesthetic determinands (taste) of 100–300
American Dairy Products Institute, Chicago, Illinois,
mg/kg. Total dissolved solids has a guideline value
USA. Retrieved from https://www.adpi.org/Portals/0/
for aesthetic determinands (taste) of 600–1,200
Standards/ConcentratedMilkPowder_book.pdf
mg/kg in the NZ Standards. The reference for
3. ADPI (1971). Dry Whey Standard, American Dairy 500 comes from EPA Secondary Drinking Water
Products Institute, Chicago, Illinois, USA. Retrieved Regulations (non-enforceable) that are guidelines for
from https://www.adpi.org/Portals/0/Standards/ aesthetic effects (such as taste, odour or colour) in
DryWheyStandard_book.pdf drinking water.
4. ADPI (1971). Whey Protein Concentrate Standard, 10. Gallier, S., MacGibbon, A.K.H. & McJarrow, P.
American Dairy Products Institute, Chicago, Illinois, (2018). Milk-fat-globule membrane (MFGM)
USA. Retrieved from https://www.adpi.org/Portals/0/ supplementation and cognition (2018). Agro FOOD
Standards/WPCStandard_book.pdf Industry Hi Tech, 29(5), 4–6.
5. Codex (1976). Codex Standard for Cream and 11. Govinda, K. (2019). Codex Sampling. Retrieved from
Prepared Creams. CODEX STAN 288-1976. Codex https://www.massey.ac.nz/~kgovinda/nzcodexdoc/
Alimentarius, FAO/WHO, Rome, Italy. concepts-of-sampling.html#apps-to-demonstrate-
acceptance-sampling
6. Codex (1995). Codex Standard for Edible Casein
Products. CODEX STAN 290-1995. Codex 12. Meena, G. S., Singh, A. K., Panjagari, N. R. & Arora, S.
Alimentarius, FAO/WHO, Rome, Italy. (2017). Milk Protein Concentrates: opportunities and
challenges. Journal of Food Science and Technology,
7. Codex (1999). Codex Standard for Milk Powders and
54(10), 3010–3024. doi.org/10.1007/s13197-017-
Cream Powder. CODEX STAN 207-1999. Codex
2796-0
Alimentarius, FAO/WHO, Rome, Italy.
13. New Zealand Ministry of Health (2018). Drinking
8. Codex (2006). Codex Standard for a Blend of Skimmed
Water Standards for New Zealand 2005 (revised
Milk and Vegetable Fat in Powdered Form. CODEX
2018). Wellington: Ministry of Health. Retrieved from
STAN 251-2006. Codex Alimentarius, FAO/ WHO,
https://www.health.govt.nz/publication/drinking-
Rome, Italy.
water-standards-new-zealand-2005-revised-2018
14. Newstead, D. F. (1999). Sweet-cream buttermilk
powders: key functional ingredients for recombined
milk products. In Proceedings of 3rd International
Symposium on Recombined Milk and Milk Products.
International Dairy Federation Special Issue No.
9902, pp. 55–60. International Dairy Federation,
Brussels, Belgium.

24 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

 2

Ingredients
15. Robinson, N., Brain, J. & Harris, K. (2019). Heat
Stability Testing of Milk Powders for UHT. Retrieved
from https://www.nzmp.com/global/en/ingredients/
types/powders/regular-whole-milk-powder/wmp-
uhtperform.html
16. Singh, H. & Tokley, R. P. (1990). Effects of pre-heat
treatments and buttermilk addition on the seasonal
variations in the heat stability of recombined
evaporated milk and reconstituted concentrated
milk. Australian Journal of Dairy Technology,
45, 10–16.
17. Srichantra, A., Newstead, D. F., Paterson, A. H. J. &
McCarthy, O. J. (2018). Effect of homogenisation
and pre-heat treatment of fresh, recombined and
reconstituted whole milk on subsequent fouling of
UHT sterilisation plant. International Dairy Journal,
87, 16–25. doi.org/10.1016/j.idairyj.2018.07.009

25
3.
Recombining
Milk
This chapter describes the process,
equipment and microbiological
controls used when recombining
milk. Also included is the stability
and shelf life of recombined milk
products and milk extension of fresh
milk with recombined milk.

26 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

27
3

Recombining Milk
3.
Recombining
Milk

Recombined milk is usually formulated to compositions Buttermilk powder can restore some of
between 8% non-fat milk solids with 3% fat (11% the membrane
total solids) and 9% non-fat milk solids with 3.5% fat
(12.5% total solids). This can be done by reconstituting When using SMP and AMF, some of the missing
whole milk powder (WMP), or a combination of skim membrane material can be restored by including
milk powder (SMP) and anhydrous milk fat (AMF), buttermilk powder (BMP). Replacing approximately 8%
with water. of the SMP with BMP gives about the same phospholipid
content as reconstituted WMP and fresh milk (Norman,
WMP retains the milk-fat-globule membrane 1955; Newstead et al., 1999).

Milk reconstituted from SMP and AMF lacks some of Using WMP avoids milk fat storage and
the natural creamy flavour of reconstituted WMP. This handling requirements
is because it lacks the milk-fat-globule material with its
phospholipid component (see Figure 3.1). The globule Using WMP, rather than SMP, as the primary ingredient
membrane is composed of a phospholipoprotein complex for recombined milk offers the advantage of not having
(illustrated in Figure 3.1), characterised by a high content to store and handle milk fat. If any variations in the
of phospholipid. proportions of fat and non-fat milk solids are required
for different products, the easiest option is to choose
a base WMP with the most convenient fat content.
Adjustments can then be made by including a portion of
SMP or cream powder as required (see Table 2.2, row 2,
Chapter 2).

Figure 3.1:
Natural fat-globule-membrane composition – source of functional components.
Phospholipid 30%
Protein 50%
Other Lipid 7%

Membrane 2%

Fat 98%

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Recombining Milk
Using an emulsifier with SMP and milk 3.1
fat formulations
Recombining process
When recombining milk from SMP and milk fat, it is
common practice to include a food-grade emulsifier, SMP and WMP are best reconstituted
such as a compound of mono- and diglycerides (see
between 40°C and 55°C. This range is
Table 2.2, row 4). This may also be used when BMP is
included in the formulation (Table 2.2, row 3, Chapter 2).
above the melting point of fat and below
Added at a rate of about 5% of the fat, such compounds the temperature at which milk proteins are
can significantly improve emulsification and reduce affected (Gibson & Raithby, 1954; Favstova,
cream layer formation. They can also affect the flavour 1962). For information on reconstituting milk
in a similar way to BMP addition. protein ingredients, refer to Chapters 8 and 9.
There is little advantage in using such emulsifiers with Smaller systems
reconstituted WMP (Table 2.2, rows 1 and 2, Chapter 2).
Any effects are barely noticeable. The semi-intact In systems with up to about five tonnes of milk per
fat-globule-membrane material in WMP means batch, milk powder may be dispersed in a simple stirred
emulsification and flavour are already superior to those batch tank, such as the Cowles dissolver which can
of SMP and milk fat formulations. handle high concentrations of solids, with viscosity up to
5000 cP, e.g. recombined sweetened condensed milk (see
Chapter 5, section 5.3). The measured amount of milk
powder is added directly to the corresponding measured
amount of water (typically at 45°C). If required, melted
milk fat can be added to the tank after the (skim) milk
powder has dissolved.
When recombining SMP and fat, systems of this type
produce only a coarse emulsion, which separates rapidly
without adequate agitation. Therefore, it is important to
homogenise the batch without delay.
To avoid this potential problem, the use of modern
high-shear mixing systems is also advised in smaller
operations. These systems can generate a finer
emulsion which is more stable to separation before
being homogenised.

Larger systems
In systems with multiple batches of 10 tonnes or more,
it is usual to circulate the water (at approximately 45°C)
from a large batch tank, e.g. 10 to 20 tonnes, through a
powder dispersion device until all the milk powder has
been added, as illustrated in Figure 3.2.

29
3.
Recombining
Milk

Figure 3.2:
Schematic diagram of a large-scale milk recombining plant adapted
from Tetra Pak Dairy Processing Handbook, Tetra Pak® (2020).

Fat
2.

Steam
Water
Milk 3.
Powder
5.
1.
4.

Fat

Hot Water 7.
Cooling
9. Medium

8.
6.

Recombination plant with fat supply to mixing vessel.

1. Tank for fat 6. Plate heat exchanger
2. Insulated pipes for fat 7. Vacuum deaerator
3. Mixer with high-shear mixing unit 8. Homogeniser
4. Mixing tanks 9. Storage tanks
5. Water heater

30 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

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EXPERT TIP:
In general, for best practice, lower
chill temperatures (≤ 7°C ) and

Recombining Milk
shorter storage times (< 12 h)
produce better-quality final products.

Hygienic ingredient handling

Whatever scale or system is used, the ingredients should Figure 3.3:
be handled hygienically. The wet and dry parts of the Flow chart for recombining process – general.
process should be kept separate until required. Milk
powder bags should be stripped of their contaminated
Dissolve WMP in Dissolve SMP in
outer paper bags. The powder in the clean plastic inner
water at 40°C–55°C water at 40°C–55°C
bag should be introduced to the critical hygiene area
before cutting the liner and emptying the powder into
the hopper or bin.
Add melted fat (at
Adding AMF approximately 60°C)
with agitation to form
AMF packed in steel drums should be completely melted primary emulsion
before addition to the reconstituted milk powder. This
takes from 24 to 48 h in a hot room at 45°C to 50°C.
The plant illustrated in Figure 3.2 allows for the melted Filter (100 μm)
milk fat, usually at 50°C to 60°C, to be added to the
reconstituted skim milk in line, directly before the
homogeniser.
Deaerate (optional)
Pasteurisation
After recombining, the milk is usually pasteurised at
a minimum temperature of 72°C with holding for a Homogenise1 Homogenise1
minimum time of 15 s, and then chilled to ≤ 7°C before (optional) 50°C–75°C 100–200 bar
being pumped to an intermediate storage tank ready for
on-processing. Pasteurise Pasteurise
≥ 72°C for ≥ 15 s ≥ 72°C for ≥ 15 s
Recombining process summaries
Cold storage periods should be kept short and
temperatures as low as possible (preferably ≤ 7°C). Chill to ≤ 7°C
However, greater control is achieved if the milk is chilled
(to ≤ 4°C) to slow microbial growth and production of
heat-stable enzymes that can affect the long-term Intermediate storage
quality of the final product. and on-processing
In summary, key processing parameters for the
recombining process are:
1. For specific homogenisation conditions, refer to particular
• Reconstitution 40°C to 55°C. product sections in Chapter 4. UHT-processed milk includes
a homogenisation step (before or after the UHT process) in
• Homogenisation 100 to 200 bar at 50°C to 75°C. addition to that indicated above.
• Pasteurisation ≥ 72°C for ≥ 15 s.
• Chilling to ≤ 7°C for intermediate storage.

31
3. EXPERT TIP:
Always run the mixing tank

Recombining
within the design parameters
for optimum mixing.

Milk

Reconstitution Sinking or submerging

The agglomerated particle becomes fully immersed in
Reconstitution is the process of making liquid milk by
the water.
dissolving milk powder in water. Powder reconstitution
is deemed complete when the powder is fully hydrated,
Disintegration
i.e. the colloidal structure of the milk protein system and
the mineral-salt equilibria have been re-established in The water moves further into the pores of the
the suspension. agglomerated particles. The large agglomerates
break into smaller aggregates and then into smaller
The milk powder reconstitution steps include wetting, individual particles.
sinking, disintegration and dissolution (adapted from
Forny, Marabi & Palzer, 2011), as shown in Figure 3.4. Disintegration completion can be determined using
One or more of these steps can take place at the particle size distribution and viscosity measurements.
same time.
Dissolution
Wetting During dissolution, the proteins become fully hydrated
The powder agglomerate establishes contact with water and minerals establish equilibrium between the colloidal
and the water starts penetrating the pore systems due and continuous phase. At the end of dissolution the milk
to capillary action. powder is considered fully hydrated.
Dissolution completion can be established by measuring
particle size distribution, viscosity and pH.

Figure 3.4:
Schematic diagram of powder reconstitution steps adapted from Forny, Marabi & Palzer (2011).

Wetting Sinking

Dissolution Disintegration

32 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

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EXPERT TIP:
Recombining high concentrations
With a powerful Cowles dissolver

Recombining Milk
agitator (15 kW for a 5-tonne batch
tank), very high concentrations can
be recombined, with viscosity up to
5000 cP, e.g. recombined sweetened
condensed milk (RSCM) (up to 75%
total solids) (see Chapter 5, section 5.3).

Time to achieve equilibrium

Figure 3.5:
Once the primary particles contact water, the colloidal
Mixing tank.
equilibrium is established very quickly, within 20 min
at 20°C. The actual time is probably shorter, but it is
difficult to make useful measurements in a shorter time
than this.
Equilibrium of minerals between the colloidal and
soluble phase is almost reached within the same period.
However, from that point on progress to final equilibrium
is quite slow. While it is possible to measure small
changes in pH and in the distribution of calcium and
phosphate between the colloidal and solution phases
over the next 48 h, this process has negligible effect on
Mixing Tank
end product properties. This re-equilibration process
continues regardless of processing, although the position
of the final equilibrium is temperature dependent, just as
it is with fresh milk.

3.1.1
Solid–liquid mixing
Good solid–liquid mixing is essential for powder
reconstitution. Depending on the scale of the process
and the dry ingredient properties, the material can be
added either directly to a mixing tank or in line. Although
in-line equipment is suitable for a continuous-flow
operation, virtually all recombining systems are batch
operated, often with very large batches of 10 tonnes
or more. Batching allows enough mixing to achieve a Create a good vortex in the liquid
uniform composition.
Axial agitators are recommended for powder mixing.
They produce a good vortex, which enables better
Mixing tanks
powder sinking. For efficient operation, it is important
In small-scale operations powder is manually added that the agitator blade speed is adjusted so the vortex
into a tank. An effective mixing tank has an efficient formed in the tank does not meet the blade (see Figure
impeller chosen for the process requirements. If the 3.6). If it does, air will be entrained and foam will result.
tank’s aspect ratio is > 1.5 it may have more than one
impeller. The tank usually has baffles to create an Add milk powder gradually
effective flow pattern.
It is also important that the milk powder is added
gradually to the agitated surface of the water (see
Figure 3.6). If the powder is dumped in large masses,
clumps of powder will become wet on the outside before

33
 3. EXPERT TIP:
It is almost impossible to break powder

Recombining
lumps once they are formed.
Avoid forming lumps in the first place

Milk
by controlling the powder addition rate.

it is properly dispersed. This will cause an impervious Powder hopper and pump systems
gelatinous coating of half-dissolved milk powder to
form around the lumps. This layer prevents the milk The most basic of these systems has a powder hopper
powder trapped inside from dispersing, and a mass of connected, via a shut-off valve, to a T-pipe placed just on
small lumps will remain undissolved. the suction side of a centrifugal pump. The pump should
be oversized for the pumping required and throttled a
Controlling each reconstitution step little to promote milk powder dispersion by turbulence
and shear as it passes through the pump. See Table 3.2
The various steps of reconstitution and how to for reconstitution steps and their process controls.
control them during mixing tank operation are shown
in Table 3.1.

Figure 3.6:
Schematic half sections (left and right) through an agitated batch mixing tank: showing good
dispersion of powder particles in the water when the milk powder is dispersed before it strikes the
vortex surface (right), and poor dispersion, resulting in lumping, when the powder is dumped onto the
surface in large semi-cohesive clumps (left).

Powder Powder

Vortex
Surface

Lumping Dispersion

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Recombining Milk
Table 3.1:
Reconstitution steps and their process controls and limitations when powder is added directly into a mixing tank.

Reconstitution step Governing event/phenomenon Controlling factor

Powder addition Manual tipping Operator’s addition rate
Sinking/submerging Vortex Impeller speed
Disintegration Agitation in the tank Impeller speed
Dissolution Contact with water after Mixing time after
disintegration is complete complete disintegration

Inline powder blending: a batch process, it is possible to provide an opportunity

for the entire batch to pass through the shear zone
Options to induct and blend powders inline are widely of the pump multiple times once powder addition is
available and can be sourced from many different complete. This option helps ensure that all powder is
suppliers including Ystral, Tetra Pak and Alfa Laval. dispersed and that the batch is homogenous. Regardless
While there are differences between designs, they of the specific configuration, these systems are capable
typically involve a powder hopper mounted above or near of entraining large volumes of air which can lead to
a pumping section capable of inducing suction which significant foaming. Care must be taken to segregate
draws powder from the hopper. In most modern designs, the powder feed system from the pump when all the
the pump also imparts significant shear and mixing required powder has been delivered. In most cases this
which greatly enhances the efficiency of the recombining is as simple as closing a valve at the base of the powder
process. These systems can be used in a continuous feed hopper.
process but are more commonly implemented in a
pumping loop with a batching tank. When configured as

35
3.
Recombining
Milk

The powder is wetted and submerged due to the This system is generally suitable for dispersing powder
pressure difference generated between the inlet and up to a concentration of 25% to 30% total solids (TS),
outlet of the pump head. It is then disintegrated by depending on the pump power and pipework size.
the shear in the pump impeller and transported to the With an adequate pump, it could be used for
mixing tank. reconstituted evaporated milk (REM) formulations
and normal-concentration milk.
After the powder disintegration is complete, the
dissolution progresses very quickly.

Figure 3.7:
Shear pump and powder feed schematic.

Powder

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Recombining Milk
Table 3.2:
Reconstitution steps and their process controls and limitations when using a powder hopper and pump set-up.

Reconstitution step Governing event/phenomenon Controlling factor

Powder addition Addition rate due to vacuum generated Pump speed
by liquid flow Valve opening
Sinking/submerging As above Pump speed
Valve opening
Disintegration Shear in the pump head Pump speed
Dissolution Contact with water after Mixing time
disintegration is complete

Figure 3.8:
Venturi disperser.

Powder
Tank

Venturi
Throat

Pump

37
3.
Recombining
Milk

Table 3.3:
Reconstitution steps and their process controls and limitations when powder is added via venturi.

Reconstitution step Governing event/phenomenon Controlling factor

Powder addition Addition rate due to vacuum generated in the Pump speed
venturi Valve opening
Sinking/submerging As above Pump speed
Valve opening
Disintegration Shear in the pump head Pump speed
Dissolution Time in contact with water after disintegration Mixing time
is complete

In-line rotor-stator mixer or high-shear rotor-stator gap ranging from 100 to 3000 µm is used
mixer systems (Karbstein & Schubert, 1995).

Rotor-stator mixers (RSMs), also known as high-shear The operating principle involves drawing the fluid axially
mixers (HSMs), have the capability to produce high shear into the rotor-stator gap; exposing it to high tangential
and energy dissipation rates (three times greater than a velocity gradients and turbulence (equivalent shear rates
mechanically stirred vessel) on a relatively smaller volume from 20,000 to 100,000 s-1) and ejecting it radially in the
of liquid (Espinoza et al., 2020). They are commonly form of jets through the stator holes (Utomo et al., 2009;
used for powder-liquid mixing in the dairy industry, Zhang et al., 2012).
especially for powders that are difficult to disperse An in-line RSM is typically used in series with a venturi
and disintegrate, e.g. milk protein concentrates, cocoa system for powder induction. However, some novel
powder and stabilisers. designs of RSM heads induct powder, in addition
RSM heads have a high-speed rotor (rotating mixing to providing the usual shear for dispersion and
element), with a typical tip speed range of 10 to 50 m.s-1, disintegration. Examples include Ystral® Conti-TDS and
in close proximity to a stator (fixed mixing element) Fristam pumps.
(Atiemo-Obeng & Calabrese, 2004). Typically, a

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Recombining Milk
Figure 3.9:
A schematic diagram of an in-line rotor-stator mixer in series with a powder induction funnel and pump
looped back to the mixing tank.

Mixing
Tank

Powder

Pump and funnel for

powder induction RSM

In the set-up shown in Figure 3.9 the water is circulated complete the entire volume is passed through the RSM
at high velocity to the mixing tank. The powder is drawn twice to ensure complete disintegration.
in from the hopper, then wetted and submerged by the
To prevent air being entrained, which causes foaming,
pressure difference between the suction side and the
the powder hopper outlet valve should be closed
atmosphere. The submerged powder is disintegrated in
immediately after all the powder has been added.
the RSM. The disintegrated powder is then dissolved in
the mixing tank. In practice, once the powder addition is

39
3.
Recombining
Milk

Table 3.4:
Reconstitution steps and their process controls and limitations when powder is added using a powder induction funnel
and disintegrated using an RSM.

Reconstitution step Governing event/phenomenon Controlling factor

Powder addition Addition rate due to pressure difference Pump speed
between the atmosphere and the Valve opening
suction line
Sinking/submerging As above Pump speed
Valve opening
Disintegration Shear in the RSM Pump speed
Dissolution Time in contact with water after Mixing time
disintegration is complete

Advanced systems
There are numerous other systems of various
complexities. The Tetra Pak® High Shear Mixer example
shown in Figure 3.10 and Figure 3.11 is fully enclosed,
including the powder delivery.
The powder can be pneumatically conveyed directly into
the batch tank containing the water, which in this version
is operated under vacuum. The vacuum draws the
powder into the dispersion tank and under the water. It
also assists dispersion by inducing the air trapped in the
powder mass to expand the whole mass into the water.
The absence of air in the vacuum chamber prevents
foam formation.
Full dispersion and disintegration is achieved by
circulating the water and powder through the RSM
(HSM) at the bottom of the tank.
These devices are very versatile and suitable for high-
concentration, high-viscosity products such as RSCM.

40 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

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Figure 3.10:
Tetra Pak® High Shear Mixer (operates under vacuum). Adapted from Tetra Pak® (2020).

Recombining Milk
Milk Fat
Water

Powder Powder

Product Outlet

Figure 3.11:
Tetra Pak® High Shear Mixer, detail. Adapted from Tetra Pak® (2020).

E
A

C
D

A. Solid fat knives, option

B B. Discharge pipe
C. Impeller
D. Perforated ring
E. Mixing vessel bottom

41
3.
Recombining
Milk

Table 3.5:
Reconstitution steps and their process controls and limitations in an automated Tetra Pak® High Shear Mixer.

Reconstitution step Governing event/phenomenon Controlling factor

Powder addition Addition rate due to vacuum Vacuum setting
Frequency of valve open-and-close cycle
Sinking/submerging Vacuum Recirculation rate
Jet mixing Vacuum setting
Disintegration Shear in the RSM Impeller speed
Dissolution Contact with water after Mixing time, typically 10 min after
disintegration is complete disintegration

3.1.2 Foaming
Precautions Comments have already been made about avoiding
foam formation. With devices such as the hopper and
This section covers recombining process precautions pump systems, and the venturi disperser (see Figure
related to water temperature, foaming and the use 3.8), it is important to keep the powder flowing through
of filters. the feed hopper. If bridging across the hopper outlet
occurs, air will be drawn through the powder mass and
Water temperature
form foam. The powder must be added as quickly as the
When dispersing milk powder using simpler devices, device can handle.
such as a basic stirred batch tank (see Figure 3.5), it is
Operators should not delay between adding bags of
essential that the water temperature is at least 40°C. If
powder into the hopper. If they do, air will be drawn
cold water (< 30°C) is used, small undissolved lumps are
down through the hopper outlet valve directly into the
highly likely to form. This causes blocked filters and loss
water (or milk) flow and foam will form rapidly. It is
of milk solids.
also important to ensure there are no leaky seals in the
Cold water can be used in the high-efficiency dispersers, pipework and pump. If there are, air will be drawn into
such as the venturi system (see Figure 3.8) operating the line to cause foam.
at low concentration, or advanced systems such as the
Different batches and types of milk powder will have
Tetra Pak® High Shear Mixer shown in Figure 3.11.
different tendencies to foam. This is mainly due to
variations in foam stability. It is best to minimise foam
formation in the first instance by using good operating
procedures, as outlined above.

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Recombining Milk
EXPERT TIP:
Avoid the most common source
of foam formation.
Liquids should not enter batch
tanks from the top, as air will be
entrained when the liquid stream
strikes the surface of the liquid in
the tank. This is the most common
source of foam formation. Tanks
should have bottom entry. If top
entry is unavoidable, the inlet
should point to the wall at an angle.

43
3.
Recombining
Milk

Summary of ways to prevent foaming When using mixers that operate under vacuum
(e.g. Tetra Pak® High Shear Mixer):
To minimise foaming during the recombining step: • Control the powder addition rate to prevent
• Add a portion of the liquid fat (2% to 3% of the final lump formation.
product) before the powder whenever possible. • Use the correct vacuum setting to minimise foaming.
• Use antifoams where permitted. • Adjust the recirculation and mixing speeds to ensure
powder dispersion without introducing air into
When adding powder directly to the mixing tank:
the product.
• Monitor the powder addition rate to avoid
lump formation. To reduce foaming after recombining:
• Control the impeller rotational speed to create • Design either bottom product entry lines for storage
a good vortex for powder sinking, but prevent tanks, or top product entry lines at an oblique angle
the vortex from touching the impeller to to the wall of the storage tank to minimise splashing
minimise foaming. and air incorporation.
• Operate with a fully submerged impeller in line • Reduce the agitator speed to maintain good mixing
with the way it has been designed. without a vortex in the mixing tank.

When using in-line powder addition equipment: Filters

• Do not allow the hopper to empty during With all powdered ingredients, there is likely to be a small
powder addition. amount of undispersed particulate residue that should
• Prevent powder bridging in the hopper outlets. be removed by filtration.
• Ensure there are no leaks in pipes or seals in the • Filters of 100 μm mesh, synthetic polymer or
suction lines. stainless steel are recommended.
• Make sure the valves on the powder hoppers are • Installations should be duplex (parallel) so
shut immediately after powder is drawn in. production can continue through one while the other
is being cleaned.
• A pressure gauge should be placed before the filter
so clogging will show as a rise in back-pressure.
• Larger filter installations (but still 100 μm mesh
size) should be used for more viscous products,
such as REM and especially RSCM, to ensure the
pressure drop across the partially clogged filter is
not too high.

44 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

 3

Recombining Milk
3.2
Homogenisation and
emulsion formation

3.2.1
Physical process
As noted in Figure 3.1 above, in natural unprocessed milk
the fat globules are coated with a robust lipoprotein
membrane. This prevents coalescence on collision.
During fresh milk homogenisation the (liquid) fat
globules are subjected to high shear and turbulence in
the homogeniser. This breaks them into many smaller fat
globules creating a surface area that is five to ten times
the original.
This new surface rapidly becomes covered with proteins
in the milk (caseins, casein micelles and whey proteins),
to form a new, stable, protective membrane. During Fat-globule membrane composition in
this process, the original natural fat-globule membrane, different formulations
although fragmented, stays in association with the fat
globules. As a result, only the new surface is coated by a • WMP: The above pattern is found in milk
new milk-protein membrane. This process is illustrated in reconstituted from WMP also. As in homogenised
Figure 3.12. fresh milk, the original membrane material remains
with the fat globules.
Figure 3.13 is a thin-section transmission electron
• SMP and AMF: In milk reconstituted from SMP and
micrograph of homogenised milk. It shows intact
AMF, there is no natural fat-globule membrane
and distorted casein micelles (dark) forming part
associated with the pure milk fat used. This means
of the membrane round the fat globules (light). The
the fat-globule surface is entirely composed of milk
thinner membrane material is composed of whey
proteins, with no natural membrane component.
proteins, individual casein molecules and original
membrane material. • SMP, AMF and BMP: In milks recombined from
SMP and AMF in which BMP is included, the natural
membrane material included in the BMP does not
migrate specifically to the fat-globule surface.
Although a proportion is found there, most is found
generally distributed through the aqueous phase.
The fat-globule membrane composition differs between
these three systems, and probably accounts for the
differences in properties referred to in Chapter 4, section
4.4.2, and Chapter 5, section 5.1.2.

45
3.
Recombining
Milk

Figure 3.12:
Schematic diagram, illustrating new surface membrane formation during homogenisation. Remaining
natural membrane is shown in black; the new, milk-protein membrane, composed of casein, micelles
and whey protein, is shown in green.

High Acceleration
and Turbulence
Fat Globules
(approx. 2 μm)

Natural Membrane
(phospholipoprotrin) Fat Globules
Valve inlet Drawn Out
New Membrane
(milk protein)

New Fat
Globules
(approx.
Valve Slit 0.5 μm)
(approx. 80 μm) (4x surface)

46 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

 3

Recombining Milk
Figure 3.13:
Fat-globule membrane structure in homogenised milk. The fat globules (f) appear light. The protein
particles and, larger, casein micelles (cm) appear black. Note the distorted casein micelles on the
fat-globule surface. The thin parts of the globule membrane are covered partly in remaining natural
membrane, partly in whey proteins and partly in monomolecular casein (McKenna, 2000).

Figure 3.14: 3.2.2

Fat-globule size distribution in recombined milk (SMP Conditions for effective
plus fat) showing the small, but significant, reduction
in fat globules in the size range > 1 μm resulting from homogenisation
homogenisation at higher temperature (70°C rather
than 45°C). Temperature
20
When a combination of SMP and AMF is used, it is
Homog 70°C imperative that the fat is properly melted (above 40°C)
before being added to the milk. Homogenisation must
Homog 45°C
be carried out above 40°C also. The higher the
Volume Frequency

temperature, the more effective the homogenisation.

Above 50°C and preferably at 70°C to 75°C (but no
10 higher than 85°C) is recommended.
Figure 3.14 illustrates the effects of homogenisation
temperature on the fat-globule size distribution in
the resulting milk.

0 1.0 10.0
Particle Diameter (µm)

47
3.
Recombining
Milk

Primary fat dispersion If the primary fat dispersion is poor, uneven regions of
high fat concentration (i.e. over about 10%) will reach
It is very important that the fat is thoroughly dispersed the homogeniser head. When this happens, the milk
to form a primary emulsion before it reaches the protein concentration is not high enough to coat the
homogeniser. In-line fat addition systems (such as in newly-formed fat surface created in the homogeniser.
Figure 3.2) should always have a mixer of some kind This results in the formation of ‘homogenisation clusters’
(e.g. a static mixer) in the line between the point of fat through impact between only partially protected fat
addition and the homogeniser. This will ensure the fat globules, which then stick together (Mulder & Walstra,
is mixed into the milk stream effectively and does not 1974). The mechanism is illustrated in Figure 3.15.
separate into a layer along the top of the pipe.
Figure 3.16 shows a fat-globule size distribution for milk
When adding fat to the batch tank, sufficient agitation that contains homogenisation clusters. The larger fat-
must be maintained while the milk is pumped to the globule clusters in this milk (> 1.5 μm) would rapidly rise
homogeniser. This is to avoid fat flotation and layering to form a cream layer.
in the tank.

Figure 3.15:
The importance of adequate mixing of fat before the homogeniser: unmixed fat (left) leads to local
high concentrations in the homogeniser, which results in the formation of ‘homogenisation clusters’.

Poorly Dispersed Fat Clustered Fat Globules

(uneven concentration)

48 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

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Recombining Milk
Two-stage homogenisation
Figure 3.16:
Two-stage homogenisation is recommended. The main
Fat-globule size distribution of homogenised
pressure is put on the first-stage valve, which has the milk containing aggregations of fat globules –
main homogenising effect. The primary function of the ‘homogenisation clusters’.
second-stage valve is to put back-pressure on the first-
stage valve. This significantly improves the effectiveness
of the first homogenisation stage by preventing cluster 20

formation (see Figure 3.17). The recommended pressure

for the second-stage valve is about 20% to 25% of the
total pressure drop across the head.

WMP compared with SMP plus fat

Frequency

When WMP is reconstituted it forms a stable emulsion 10

directly, even without homogenisation. This is because
it is well emulsified during the powder manufacturing
process and the emulsion structure remains intact
through the drying and reconstitution processes. This
effect persists in products that are homogenised,
regardless of the ingredients chosen, as happens in the
manufacture of UHT-sterilised recombined milk. 0
0.1 1.0 10.0 100.0
The milk made from WMP gives a more stable emulsion, Particle Diameter (µm)
less prone to cream layer formation than the SMP-plus-
fat system.

Dispersion and incorporation of additives

Figure 3.17:
When using additives, such as emulsifiers, carrageenan Disruption of fat globules in first and second stage of
or other hydrocolloid gums (the latter are sometimes homogenisation (adapted from: Tetra Pak®, 2020).
used to increase viscosity), it is vitally important that
these are properly incorporated.
After First Stage After Second Stage

Some powdered additives may be best dry blended

with milk powder before addition, while others may be
best pre-dispersed in hot or cold water. Following each
additive supplier’s advice on how to best incorporate it in
the product is strongly recommended.
The majority of these substances do not dissolve or
become active until homogenised, in most cases at
about 70°C. It is therefore important to ensure that they
are fully dispersed when mixed and remain effectively
suspended (by adequate tank agitation) as the milk is The vat should be inspected after pumping out, to ensure
pumped to the homogeniser. there is no additive sediment lying on the bottom.

49
3. EXPERT TIP:
The faster you can process your milk

Recombining
the better the quality your finished
product will be.

Milk
Microbiological growth still occurs at
chilled temperatures,at a reduced rate,
resulting in enzyme production and
therefore reduced shelf life.

In-process control and diagnostic measures more heat resistant. In milk, these are killed by heat
(microscope) treatments equivalent to a minimum of 72°C for a
holding time of at least 15 s. Minimum pasteurisation
It is recommended that the effectiveness of conditions are regulated by law in most countries.
emulsification, homogenisation and dispersion of
hydrocolloid gum material be checked routinely using a Pasteurisation to eliminate spoilage organisms
light microscope. Examination using a light microscope is
In addition to killing the harmful bacteria, pasteurisation
very quick and simple, and the result is seen instantly. A
eliminates most spoilage organisms that can grow
good-quality instrument capable of 400× magnification
at low temperatures (≤ 7°C), such as psychrotrophic
using transmitted light is suitable, but a phase-contrast
bacteria, yeasts and moulds. This prolongs the shelf life
capability is an advantage.
of milk kept under refrigeration.
For a clear view of homogenised milk emulsions, it is
Bacillus and Clostridium spores, including those of the
recommended to dilute the sample to give a fat content
pathogen Bacillus cereus, are invariably present at low
of 0.5% to 1%. Otherwise, the fat globules in the image
levels in milk. Although vegetative (growing) cells are
are too crowded to allow clusters to be seen. However,
killed, these spores can survive pasteurisation.
when inspecting for effective dispersion or dissolution of
gum stabiliser systems, it is best not to dilute the sample
When to pasteurise
and not to agitate it vigorously.
All milk should be pasteurised without delay. Recombined
Defects, such as oversized fat globules, homogenisation
milk should be pasteurised immediately after the
clusters (discussed above) or aggregated material, due
recombining process and fresh raw milk should be
to unfavourable process conditions are easily detected
pasteurised immediately on receipt at the factory.
with the microscope.
Refrigeration
3.3 During intermediate storage, the milk temperature

Milk handling and should be kept below 10°C, preferably ≤ 4°C. This means
adequate refrigeration must be provided in the plant.
microbiological control Most defects caused by microorganisms can be avoided
if the milk is managed so that at no time (cow to
Liquid milk is not a stable product; consumer) does the aerobic plate count (APC) ever
microbiological deterioration will occur if exceed 106 colony-forming units (CFU)/mL.
proper precautions are not taken. Milk can
carry disease organisms if it is not properly Maintaining pasteurisation equipment
treated. Pasteurisation equipment must be maintained in
good repair and in a state of good hygiene. The
Pasteurisation to eliminate harmful bacteria heat-exchanger sections and pipework after the
The pasteurisation process is designed to eliminate pasteurisation section must be clean and in a sanitary
zoonotic (from other animals to human transferring) condition so recontamination cannot occur.
pathogenic (harmful) microorganisms from the milk.
It is important to check the calibration of pasteuriser
The most heat resistant of these are Mycobacterium
temperature sensors and controllers regularly.
tuberculosis, which causes tuberculosis, and Coxiella
burnetii, which causes Q-fever. The latter is the

50 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

 3
EXPERT TIP:
A minimum recombining temperature
of 50°C, held for no longer than 7 h, is

Recombining Milk
recommended to limit B. cereus and
S. aureus growth to < 1-log10 CFU/mL
(see Figure 3.19).

The pasteurised milk may also be tested routinely by the Mitigating B. cereus and S. aureus risks
standard method for alkaline phosphatase. This natural
milk enzyme is inactivated by normal milk pasteurisation During extended process times at temperatures of 8°C
conditions. That means a negative test result is a useful to 55°C, there is a risk that any B. cereus and S. aureus
confirmation that a heat treatment at least sufficient present may grow to sufficient numbers that allow for
for pasteurisation has been achieved (MPI, 2022; the production of heat-resistant toxins. This can cause
MPI, 2019). illness in consumers of the final product, even after UHT
heat treatment.

3.3.1 The optimum growth temperature of B. cereus and

S. aureus is 30°C to 40°C (see Figure 3.18). To mitigate
Temperature–time guidelines for this toxin risk, B. cereus and S. aureus levels are typically
food safety limited to no more than 1,000 CFU/mL. A limit of 1,000
CFU/mL has a 2-log10 safety as since B. cereus and
This section addresses temperature–time guidelines, S. aureus are not likely to produce toxin until they reach
during recombining and chilled storage, to maintain final 100,000 CFU/mL.
product food safety quality.

Figure 3.18:
Comparison of the growth rate of B. cereus, thermophiles and psychrotrophic bacteria at varied temperatures.
B. cereus and S. aureus (mesophilic bacteria) have a similar optimum growth temperature range (30°C to 40°C),
and B. cereus has a faster growth rate than S. aureus; therefore, B. cereus is used as the model organism to predict
growth and toxin production by both B. cereus and S. aureus.

1.8

1.6 Psychrotrophic
Bacteria
1.4
Growth Rate √μ (max)

1.2
Mesophilic
1.0 Bacteria

0.8
Thermophilic
Bacteria
0.6

0.4

0.2

0
0 10 20 30 40 50 60 70 80 90

Temperature (°C)

51
3. EXPERT TIP:
Limiting the recombining time to

Recombining
3-5 h, at target temperatures of
55°C–60°C, lowers the quality risk

Milk
associated with thermophile growth.

At the start of recombining, an initial worst-case number defects such as bitterness, and quality defects such as
of B. cereus and S. aureus is estimated to be 100 CFU/ gelation in final product during shelf life. Spores may
mL. Therefore, the aim is to design the temperature– cause sterility defects in final product when it is stored at
time profile of a process that would limit growth to > 30°C to 40°C, with a mild-quality defect described as
less than a 1-log10 increase during recombining. That a flat-sour sensory effect (where the bacteria produce
way there would be a low risk that numbers exceed acid but no gas, so the packaging appears normal i.e.
1,000 CFU/mL. 'flat', and does not appear bulged).
At > 50°C the growth rate is slower than at lower The ability of thermophiles to produce enzymes, including
temperatures (i.e. 30°C to 50°C) (see Figure 3.18). heat enzymes, varies greatly between strains, as does
Consequently, growth is predicted to be limited to less the ability of thermophilic spores to resist heat, including
than a 1-log10 increase in numbers when the recombining UHT treatment. This makes it difficult to establish a
time does not exceed 7 h and a recombining temperature total thermophile (sum of vegetative cells and spores)
of > 50°C is maintained (see Figure 3.19). B. cereus was limit to prevent enzyme production or a thermophile
used as the model organism, as it has a faster growth spore limit to prevent sterility defects in final product.
rate than S. aureus. However, an in-process thermophile limit of 100,000/
mL and an in-process thermophilic spore limit of 1,000/
If < 50°C, a shorter time required mL is recommended using the 100°C for 30 min method.
If the temperature drops below 50°C, or the recombining The ratio of spores to vegetative cells can vary among
time exceeds 7 h, an in-process sample may be tested to thermophile strains. So, when total numbers reach
count B. cereus and S. aureus, to determine whether the 100,000/mL, some strains may have < 1,000/mL of
in-process limit of 1,000/g for either has been exceeded. spores while others could have more.
However, it can take about 48 h to receive a result. This If an unheated liquid is held in a recombining tank it
may be too long to hold the product in the aseptic tank typically cools at a constant rate. When product cools
before packing, so the product may have to be packed at a constant rate from 60°C to 55°C over 7 h, it is
before obtaining a test result. This runs the risk of predicted that thermophile numbers will be limited to a
rejecting packed product if a result was obtained where 1 log10 CFU/mL increase after 5 h, but increase by 3 log10
the limit is exceeded. As the product is usually thoroughly CFU/mL after 7 h (see Figure 3.20).
agitated and mixed during recombining, the counted
result of sampling for in-process micro testing is likely to UHT spec ingredient milk powders typically have
represent the complete batch. thermophile numbers of 1,000 CFU/g and are typically
added at approximately 10% of the formulation. This
When a recombining temperature of 30°C to 40°C is results in < 100 CFU/g when recombining begins. If it is
required, it is recommended to limit the recombining assumed that 100 CFU/g of thermophiles are present
time in this temperature range to < 3 h. at the start of recombining, it is predicted that numbers
would reach 3 log10 CFU/mL after 5 h and 5 log10 CFU/
Controlling thermophiles during recombining mL after 7 h (see Figure 3.20). Therefore, limiting the
Recombining at 50°C to 60°C is close to the optimum recombining time to 3 to 5 h, at temperatures of 55°C to
growth temperature of thermophiles (Geobacillus 60°C, lowers the quality risk associated with thermophile
and Anoxybacillus) (see Figure 3.18). Thermophiles are growth. In addition, it is recommended to perform
spoilage organisms. They do not cause illness, but can in-process testing for thermophiles and thermophilic
produce heat-resistant enzymes and spores. Enzymes spores before UHT heat treatment to ascertain the risk,
produced by thermophilic bacteria can remain active particularly for those processes where product is held at
after UHT heat treatment. They can cause sensory 50°C to 70°C for > 3 h.

52 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

 3
Figure 3.19:
Predicted growth of B. cereus at 50°C. It is predicted to take 7 h for B. cereus to increase from a

Recombining Milk
worst-case initial number of 100 CFU/mL (2 log10) to 1,000 CFU/mL (3 log10) when the recombining
temperature is maintained at > 50°C.

Growth of B. cereus
(Temperature, 50°C)
9.0 65

8.0
60
7.0

Temperature (°C)
6.0 55
IogcCFU/g

5.0 Temperature
50
4.0

3.0 45

2.0
40
1.0

0.0 35
0 1 2 3 4 5 6 7 8 9 10 11 12
Time (h)

Figure 3.20:
Predicted growth of B. cereus and thermophiles when product cools at a constant rate from 60°C
to 55°C after 7 h. It is predicted that B. cereus growth is minimal. If it is assumed that the number
of thermophiles in the formulation when recombining starts is 100 CFU/mL (2 log10 CFU/mL), it is
predicted that numbers would reach 3 log10 CFU/mL after 5 h, and 5 log10 CFU/mL after 7 h.

Growth of B. cereus
and Thermophiles
(Temperature, 60°C—55°C)
9.0 65

8.0
Temperatu
re 60
7.0
Temperature (°C)

6.0 55
IogcCFU/g

5.0
50
4.0

3.0 45

2.0
40
1.0

0.0 35
0 1 2 3 4 5 6 7 8 9
Time (h)

53
3. EXPERT TIP:
Robust prediction modelling will

Recombining
save time and money.
Prediction modelling will reduce

Milk
the need for multiple plant trials
to determine the best processing
time and temperature profiles to
manage product quality in your
manufacturing plant.

Controlling risk organisms at chilled defects in final product. It is estimated that the initial
temperatures psychrotrophic bacteria number in the stock tank would
be approximately 1/g, assuming pasteurisation has
The key risk organisms for quality/spoilage at chilled occurred and sanitary conditions prevail. It is predicted
temperatures are the psychrotrophic bacteria, such that at temperatures of < 10°C, it would take > 72 h
as Pseudomonas. and the spore formers Paenibacillus. for Pseudomonas to increase from 1/g to 100,000/g
Psychrotrophic bacteria tolerate near-freezing (see Figure 3.21).
temperatures but with slower growth rates than at
higher temperatures. They can produce heat-resistant It is recommended to hold product at < 10°C in the stock
enzymes that can cause quality defects in final product tank for a target of < 24 h, with a maximum time of
during shelf life if their numbers reach 106 to 108 CFU/ < 72 h, to prevent growth and production of heat-
mL. However, for some high-functionality, specialty UHT resistant enzymes by psychrotrophic bacteria. Ideally
products, Pseudomonas numbers > 100,000/g, before product should be stored at ≤ 4°C, rather than < 10°C, to
UHT heat treatment, have been shown to cause quality further protect the quality, however some plants don’t
have this capability.

Figure 3.21: Figure 3.22:

Combase model predicting the growth of Pseudomonas Combase model predicting the growth of B. cereus
at 10°C and a pH of 6.8 for 72 h. It is predicted that at 10°C and a pH of 6.8 for 72 h. It is predicted that
with initial numbers of 1 CFU/mL, numbers would reach after 72 h, growth is limited to within a 1 log10 CFU/mL
100,000 CFU/mL after 72 h. The minimum temperature increase in numbers.
for toxin production by B. cereus is 8°C, and by S.
aureus is 10°C. Therefore, to eliminate the risk of toxin
production, milk could be stored at ≤ 7°C. However, if
milk is stored at < 10°C, growth by B. cereus and
S. aureus is minimal and numbers are unlikely to reach
thresholds required for toxin production to begin
(see Figure 3.22).

IogcCFU/g
IogcCFU/g
10
10

8
8

6 6

4 4

2 2

0 0
0 10 20 30 40 50 60 70 0 10 20 30 40 50 60 70

Time (h) - 72.0 + Time (h) - 72.0 +

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Recombining Milk
3.4 Fortuitously, water removal not only facilitates transport
of milk solids but is also key to achieving the stability
Stability and shelf life required. Figure 3.23 will be well-known to most
readers and shows the relationship between water
activity, a measure of the water not bound tightly
3.4.1 to food molecules, and food stability, measured by
Introduction critical degradation rates. Raw milk and recombined
milk are wet foods with high water activity (> 0.95),
The main reasons to recombine are to avoid transporting while powders and AMF are dry foods, with low water
water and to maintain food stability for cost-effective activity (< 0.25).
delivery of quality products to consumers. This section
holistically examines the stability side of recombining by To generalise, recombining is a technique that takes
following milk solids from cow to consumer. milk, a low-stability food with high water activity, and

Figure 3.23:
Qualitative effects of water activity on degradation mechanisms in food, therefore defining wet foods, intermediate
moisture foods (IMF) and dry foods. Typically, recombining uses dry foods as ingredients and converts them into wet foods.

Dry Food IMF Wet

Lipid
Oxidation
Non-enzyme
Rate

Browning Hydrolytic
Deterioration Rate

Reactions
Relative Deterioration

Growth
of Moulds
Relative

Enzyme Yeasts
Activity
Bacteria

0 0.2 0.4 0.6 0.8 1.0

WaterActivity
Water Activity

55
3. EXPERT TIP:
Make like-for-like comparisons.

Recombining
When comparing sources of milk
solids, express quality results per

Milk
100 g of fat or protein to allow
for fair comparisons.

stabilises it for transport as a low-water-activity, dry For sensory assessments, it is not appropriate to
food before adding water back to give a less stable adjust sensory scores to solids content. Consequently,
product (recombined milk) to cover ‘the last mile’ to the ingredients should be compared, at a minimum, using a
consumer. For this strategy to work, there must be a model that makes compositions equivalent, and ideally
threshold for degradation at both low (small amounts) by conducting an appropriate pilot trial.
and high water activity (greater amounts). To be within
Colour is an attribute that is least likely to be expressed
allocation, milk solids must behave as expected at both
using appropriate units. But doing so is important
water activities. Critically, stability at low water activity
because it implies that, at equivalent amounts of ‘brown
is not indicative of stability at high water activity,
colour’, MPC would be preferred over SMP due to less
creating risks and opportunities. This is an area that
‘brown colour’ per gram protein.
can be navigated if the science is understood and the
section’s aim is to convey the relevant science. 3.4.2
Note: Units Terminology: Stability versus shelf life
The units used in Figure 3.23 for reaction rates are Shelf life is a controversial subject area and even the
corrected to moisture content or, by difference, total definitions of shelf life are controversial. A generalisation
solids. For recombining, it is critical that units are always is to state that shelf life is the time where a product
corrected in this way to clearly follow relationships is fit for purpose. But what is ‘fit for purpose’? For
between ingredients and products containing different instance, when does a cooked or caramel flavour
water content. Not only does this allow the product become an unacceptable defect? Also, a shelf life can
stability to be easily traced back to ingredient stability either be retrospective (based on what was observed)
but it also enables the accurate comparison of or predictive (based on what you think might happen).
ingredients. Preferably, units should reflect the solids Shelf life might also mean the behaviour of only one
that are relevant (e.g. fat or protein). This might seem specific sample, or maybe the average of a batch of
obvious but requires discipline given a wide variety of samples or maybe the ‘worst-case’ scenario.
units in common use in the industry.
Those who work in recombined product development
For example, when choosing a source of milk fat for will tend to think of shelf life as the date and other
recombining; some of the possible options are AMF/ relevant information stamped on packaging. This is
FFMR (99%+ fat), milk powder (approximately 30% obviously predictive, however, although predictions might
fat), or fresh or frozen cream (approximately 40% fat). be based on past results and probably are intended
A relevant quality measure would be the content of to reflect a population of samples while recognising
free fatty acids (FFA). The units used to measure FFA that individual packs can give different results after
in creams and powders are usually the same (millimole experiencing different supply chains and in use by
per kilogram product) but 1 mmol/kg of product will different consumers.
have more impact on recombining when using a 30%
Fortunately, there is a simpler, and scientific, concept
fat powder than when using a 40% fat cream because
that can be used called stability. Stability is defined
less cream is needed to deliver the same fat content.
as the retrospective (i.e. not predicted) rate of change
Therefore, it makes sense to convert units to grams oleic
measured under precisely controlled scientific conditions.
acid per 100 g fat, the typical measurement used for
In this section, the focus will be on stability (being
AMF/FFMR to compare all three products fairly.
scientific and less controversial) and will be discussed in
a relative, not absolute, way.

56 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

 3
EXPERT TIP:
Shelf life ambiguity is often due
to the level of risk tolerated, not

Recombining Milk
product differences.
It is not unusual for the same food
products to be given different
shelf lives because of differences in
tolerance for risk. Take care when
interpreting shelf life claims.

3.4.3 3.4.4
Stability measurements and Shelf life inconsistencies
shelf life predictions Considering the above it is not unusual to find
Stability is simply determined by making assessments inconsistencies in shelf life in recombining. For example,
(sensory evaluations, chemical measurements, etc.) in shelf lives for recombining ingredients (e.g. milk powders,
a scientific objective manner as a function of time AMF etc.) may differ between suppliers providing
and temperature. Often this is referred to as a storage the same ingredients. Non-dairy ingredients (e.g.
trial, or, ambiguously, a shelf life trial. A storage trial is vitamins) might also have different shelf lives, supplier
often the first step to predicting shelf lives but doesn’t dependent. Finally, recombined products made using
have to be. the same ingredients and same basic process might
be given different shelf lives depending on who the
Shelf lives are usually determined by taking the manufacturer is.
information from stability measurements and other
data and then considering the following: Often, the largest inconsistency is between academia
and industry. For instance, Lloyd et al. (2009), have
• What are the acceptability limits for the attributes
questioned the US industry standard for milk powder
that are changing (e.g. when does an off-flavour
become unacceptable, and to whom)? shelf lives. However, the stability data they presented
appeared consistent with all other available data.
• What environmental temperatures will each sample
The only difference in their work was a conservative
encounter and how to allow for this?
interpretation of the data.
• What do local regulations dictate in the approach
to predicting shelf life? It wouldn’t be appropriate for this text to dictate how
• What are the commercial, legal, and marketing much risk businesses should take when investing in
implications of a chosen shelf life? developing recombined products. Therefore, definitive
• What is the likely batch-to-batch variability in the shelf life statements are not made and instead only
composition and stability of a product? presented are known trends for stability of milk solids
when recombining.
• What are the risks of a shelf life being too short
(e.g. food waste) or too long?
• Does a margin of safety need to be applied to the
data? How reliable is the data?
Overall, shelf life predictions, as stamped on products,
are business decisions that balance risks and rewards,
but they must consider storage trial data. There is no
prescribed way of doing this, except local regulations
need to be considered.

57
 EXPERT TIP:
Phase changes in a product are a
telling sign of instability.
Recombined creams, for example,
are best kept chilled to avoid melting
and recrystallisation of milk fat.

58 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

 3
3.
Recombining

Recombining Milk
Milk

3.4.5 • Enzymatic hydrolysis reactions (lipolysis and

proteolysis) and physical reactions have low
Effects of temperature and light activation energy and tend to determine
on stability recombined finished product stability (along
with oxidation).
Temperature • Stability measurements at high temperatures
Most causes of instability in the recombining journey lead to abundant high activation energy reactions
from cow to consumer are temperature dependent. (e.g. browning) that wouldn’t be so abundant at
Temperature is related to phase changes (e.g. melting low temperature. Therefore, measurements at
of milk fat in recombined cream) and rates of chemical/ high temperature have limited value in predicting
physical reactions. behaviour at low temperature.
Phase changes are best avoided. For example, The effect of temperature on some causes of instability
recombined creams are always best kept chilled to is summarised in Figure 3.24.
avoid melting and recrystallisation of milk fat causing
The range of activation energies encountered during
coalescence. Otherwise, most temperature effects
recombining determines a useful generalisation that
are best understood as being related to rates of
every 10⁰C increase in temperature will approximately
chemical and physical ‘reactions’. Conceptually and
halve stability. Where average temperatures
mathematically, these effects can be modelled based
encountered in the journey from cow to consumer
on ‘collision theory’. When collision energies exceed
are uncertain, this rule can be used to estimate the
the energy required for reaction (activation energy),
uncertainty in the stability of milk solids and therefore
reactions occur. As the temperature rises it becomes
uncertainty in what the consumer will experience.
more likely that the most energetic species in a sample
will have energies exceeding the activation energy. If the For instance:
activation energy is low, temperature is less important
• Assume during the entire recombining journey it
than when the activation energy is high. This is the
takes 18 months for milk solids to travel from cow
basis of the Arrhenius equation explained in more detail
to consumer (12 months as ingredients e.g. milk
elsewhere (van Boekel, 2008).
powder and AMF, 6 months as a recombined milk
Activation energies and the associated temperature- product).
dependence of reactions have some critical implications • Assume the average temperature during that
when recombining:
process lies between 17⁰C and 27⁰C.
• Oxidation reactions of milk fat have low activation • Then to the consumer, the variability in the quality
energy – therefore, milk fat needs to be frozen for of the milk solids will be equivalent to 12- to
collision energies to mostly be below the activation 24-month-old milk solids, depending on what the
energy for oxidation, making the use of FFMR a actual average temperature was.
good strategy.
The above considerations make it important to allow for
• Browning reactions of non-fat powders (MPC/ substantial variations in apparent stability and shelf life,
SMP etc.) have high activation energy – including unexpected gains (the situation may not be as
consequently ambient transport and storage is bad as it seems) and unexpected setbacks (it may be
usually acceptable for non-fat powders. worse than originally thought).

59
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Recombining
Milk

Figure 3.24:
Indication of how key degradation mechanisms respond to changes in temperature.

Fat
melt
ing

Oxi
dat
ion
Time Required (log scale)

Br
ow
ni
ng

Enzym
atic r
eactio
ns

0 10 20 30 40
Temperature °C

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EXPERT TIP:
Allow for degradation accumulating
in both ingredients and products.

Recombining Milk
However be aware that suppliers may
have also made recommendations
based on such allowances. If the
overall combination of allowances
becomes too conservative, some
opportunities may be missed.

Light secondary shelf life. This applies to extended-shelf-life

milks, pasteurised milks, and other pasteurised products
Light is closely related to temperature as a form of like yoghurts. For these cases the main consideration for
energy. However, light tends to be a more targeted an ingredient is that it yields an acceptable recombined
form of energy that can do more damage. Because the product. If an ingredient does yield an acceptable
effects of light can be readily avoided by using opaque recombined product, the shelf life of the recombined
packaging, it is recommended opaque packaging is used. product will likely be the same regardless of whether the
However, it is not impossible to create viable recombined ingredient is 2 days or 2 years old.
products in transparent packaging, although that is a
specialised topic. For example, if milk powder and AMF are used to make
a pasteurised milk, the shelf life will always be limited
by microbial spoilage to less than approximately two
3.4.6 weeks, regardless of ingredient age. Therefore, ingredient
Primary (ingredient) and secondary age is less important as an acceptance criterion.
(product) shelf life and stability Ingredients can still be used for recombining towards (or
considerations even after) the stated shelf life if they have acceptable
flavour and functionality (and so will produce an
Usually both ingredients for recombining (e.g. milk acceptable product).
powders or vitamins) and recombined products are The situation is very different for causes of instability
assigned shelf lives. The first is assigned by the ingredient that are less dependent on water activity. These include:
supplier and is called the primary shelf life; the second
is assigned by the recombined product manufacturer • Lipid oxidation and associated off-flavours.
and is called the secondary shelf life. In some cases, the • Protein ‘denaturation’ and associated
primary and secondary shelf lives are related and in functional changes.
other cases they aren’t. Understanding and allowing for • Maillard browning and associated off-flavours.
this distinction can be critical to successful recombining.
In recombining scenarios where shelf life is limited by
As already explained by Figure 3.23, some causes of the above, primary and secondary shelf life start to
instability (e.g. microbial growth) are only significant become related and it is important to consider primary
at high water activity. In these cases, primary and (ingredient) shelf life when setting secondary (product)
secondary shelf lives are not usually related because shelf life. This mostly applies to long-life products such
water is not significant during the primary shelf life. as UHT-sterilised or retort-sterilised milks or evaporated
This applies to: milks and UHT-fortified milks.
• Microbial spoilage. The critical consideration is that degradative changes are
• Lipolysis. occurring in both the ingredient (low water activity) and
• Proteolysis. the product (high water activity) and are accumulating.
The changes that occur during ingredient storage
• Physical instability (fat rise, sedimentation, gelation).
are not undone when a recombined product is made.
• Miscellaneous hydrolysis reactions. Subsequent sections will provide more quantitative
Therefore, in recombining scenarios where shelf life detail on the accumulating changes.
is limited by the above, it is not necessary to give Inevitably this means an old ingredient (near the end of
much attention to the primary shelf life when setting primary shelf life) will lead to a shorter secondary shelf

61
3.
Recombining
Milk

life than a young ingredient. For instance, if shelf life accumulation of degradation, some collaboration and
in evaporated milk was limited by browning, a young negotiation may be needed.
powder (white colour) would be expected to last longer
than an old powder that had already developed some
brown colour.
3.4.7
Protein degradation:
For these scenarios, the common practice of not
accepting ingredients whose age exceeds half the shelf
browning reactions
life appears useful to balance between primary and The browning reactions that affect protein are an
secondary shelf life. However, if the ingredient supplier excellent example of points raised earlier and provide a
has set the primary shelf life to allow for further changes good starting point for discussing specific degradation
in the secondary shelf life the allowance may be twice as mechanisms. There are numerous ways to measure
much as it needs to be. To prevent both the ingredient browning but a preferred way is by measuring
supplier and ingredient receiver both allowing for furosine, specifically in units of milligrams furosine per
gram of protein.

Figure 3.25:
Illustrative furosine variations across related recombined and fresh products.

mg of furosine per 100 g protein

0 500 1,000 1,500 2,000

Raw milk 0

Pasteurised milk 10–50

Fresh powder 100–300

Ageing powder 250–1,250

Direct UHT-sterilised milk 50–100

Direct UHT-sterilised milk

(from fresh powder) 100–300

Direct UHT-sterilised milk

(from ageing powder) 300–1,000

Aged UHT milk 50–1,500

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Recombining Milk
Consequences of browning To put this into practice would require setting a limit for
reactions (furosine) furosine. As a marker for browning, the furosine content
can be related to:
Furosine, browning and other attributes are all
connected through a series of reactions called the • Brown colour.
Maillard reaction. The underlying chemistry is beyond • Flavours, positive and negative, derived from
this discussion, but comprehensive reviews are available browning (e.g. caramel).
(Newton et al., 2012). • Aspects of protein nutritional quality
Figure 3.25 shows the furosine contents typically found (available lysine).
in protein ingredients and in recombined products • Sediment formation, particularly brown
made from those ingredients with a comparison to polymeric melanoidins.
equivalent non-recombined products. The data reflects • Functional changes due to protein cross-linking.
that browning (including furosine formation) tends to
be faster in powders than in liquids but in liquids it still Therefore, if a limit for furosine were set, it would be
happens (albeit at a slower rate). A further complication based on the most limiting factor from those listed
is that browning also happens during heat treatments in above. There are no regulatory limits for browning except
milk processing. those applying to fresh milks (to prevent unlabelled
recombining). However, there is ongoing debate about
Because recombined products will contain more furosine placing regulatory limits on browning, particularly for
than equivalent fresh products, some have suggested susceptible populations for various reasons.
that furosine measurement can be used to distinguish
recombined products from fresh products. Some In the absence of clear limits for furosine, the reality
regulators are also incorporating furosine measurements therefore is that a quantitative ‘furosine allowance’ is
into checks to identify recombined milks that are falsely not used to develop recombined products and establish
marketed as fresh milks. Obviously recombining of fresh shelf lives. However, the qualitative principles are still
skim milk with AMF cannot be identified by furosine useful. For instance, if wanting to decrease the brown
measurement and there is a risk that some fresh milks attributes experienced by consumers, the first step is to
are falsely identified as recombined because of their identify the change that will have the biggest impact on
temperature–time history. the budget. For pasteurised recombined milk, this will be
the ingredient, and a frozen concentrate would be worth
Based on Figure 3.25, it is argued that all long-life considering. But for a retort-sterilised evaporated milk
products eventually end up with high levels of furosine, with a long secondary shelf life, the ingredient may make
given enough time, regardless of how they were made. minimal contribution.
But there is always an option to set shelf lives so that
furosine does not exceed a specific level. If so, based It is noteworthy that furosine is also used as a
on Figure 3.25, after allowing for the furosine formed temperature–time indicator. In this case, furosine is
during processing the remaining furosine can be indirectly related to other degradation mechanisms (e.g.
allocated between primary (ingredient) and secondary lipid oxidation) simply because temperature and time
(product) shelf life. determine most types of degradation.

Characteristics of browning reactions

Furosine can be used as a temperature–time indicator
because, at constant temperature and water activity,
browning (Maillard) reactions are invariably zero-order

63
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Recombining
Milk

Figure 3.26:
Illustration of how browning reactions and oxidation reactions proceed with time during storage.
Amount of Defect

ns
ctio
a
re
g
nin
ow
Br

Oxidation
reactions

time
Induction

Storage Time

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Recombining Milk
reactions. A zero-order reaction is a reaction where the physical changes (gelation, sediments) are due to
rate does not change as the concentration of reactants proteolysis without supporting evidence. Physical
changes. Therefore, as reactions occur during storage changes can occur through other mechanisms.
they do not slow or accelerate. As illustrated in Figure
Like lipolysis, proteolysis does not occur in the absence
3.26, there is a steady increase in measures of browning
of water and will not occur in ingredient powders.
with storage time at constant storage conditions.
Consequently, proteolysis only plays a role in secondary
Theoretically, with browning being zero-order this (product) shelf life. Normally, proteolysis should occur at
makes it relatively straight-forward to budget for a negligible rate in liquid dairy products at neutral pH.
the accumulation of browning. All that one needs to Proteolysis only becomes an issue if protease enzymes
know is the browning rate in the ingredient and in inadvertently make it into ingredients and therefore
the recombined product. For instance, if the powder recombined products. This risk is small but well-known,
browning rate was 5 milligrams furosine per gram of as evident by vast literature on the subject (e.g. Stoeckel
protein per week, and the recombined liquid rate was et al., 2016).
2, it is possible to calculate when browning would be
The controls required for proteolysis are much the same
unacceptable if a limit was set at 200. Twenty weeks of
as for lipolysis, and considerations include:
powder storage and 50 weeks of liquid storage or
30 weeks of powder storage and 25 weeks of liquid • Heat treatments applied during recombining can
storage would both be enough to exceed the threshold. decrease, but not eliminate, risks of proteolysis by
In that respect, browning is easier to predict than other deactivating enzymes.
causes of degradation. In addition, it is possible to • The activity of protease enzymes depends on the
monitor how ingredients and recombined products are formulation. Therefore, significant changes to a
tracking against a budget by making measurements at formulation can change susceptibility to proteases.
critical points.
• The types of functional defects and off-flavours
that form due to proteolysis depend on the enzymes
3.4.8 and proteins involved.
Protein degradation: proteolysis • An appreciation of the non-linear relationship
between enzyme concentration and severity
In this section we do not consider intentional proteolysis of defects. In practical terms, this can mean
induced by adding rennet to make recombined cheese that a small decrease in enzyme concentration
products (see Chapter 9). may give a surprisingly positive improvement,
Proteolysis is the reaction of protein with water whereas a small increase may make the problem
(hydrolysis) to form peptides and free amino acids. disproportionately worse.
Consequences of proteolysis include:
• Functional changes (gelation and/or sedimentation).
3.4.9
• Off-tastes (bitter, umami, sour).
Fat degradation: lipid oxidation
• Off-flavours (e.g. broth, vegetable). Introduction to oxidation
• pH decrease.
Degradation of fat (lipid) can be through lipolysis
Usually the most significant consequences of proteolysis (requires water) or oxidation (water not required).
the bitterness, which can be extreme, and the physical Therefore, when recombining, it is more important
changes. However, it should not be assumed that to understand oxidation than lipolysis because

65
3. EXPERT TIP:
Dilution is not a solution for

Recombining
oxidised ingredients.
Avoid attempting to mask oxidised

Milk
ingredients by dilution; doing so
could initiate oxidation in the new
material and exponentially produce
off-flavours.

oxidation can accumulate in ways that make ingredient • AMF and WMP are similar products with respect
choices critical. to oxidative stability and use an ambient supply
chain while controlling oxidation by monitoring
The concepts presented here can be applied to WMP,
(reactive) oxygen by use of inert gas flushing during
fat-filled milk powder, dairy fats (AMF, FFMR, frozen
ingredient packing (see Chapter 2, section 2.3.1).
cream), non-dairy fats (e.g. vegetable oils, algal oils,
fish oils and blends of these), and milk fat/vegetable oil • FFMR and frozen cream are similar products
blends. Blends of vegetable oils and milk fats are used to with respect to oxidative stability and use frozen
achieve milk fat flavour (diluted) while also gaining some supply chain to control oxidation while not
of the value (e.g. cost savings, nutritional claims) that controlling oxygen.
comes from using vegetable oils. • Overall, the frozen ingredients are more oxidatively
stable and predictable than the ambient
Oxidative stability is dependent on both temperature
ingredients but not by enough to justify always
and, as the name implies, (reactive) oxygen. But oxidative
using frozen ingredients.
stability has little dependence on water content. This
leads to the following generalisations about ingredients • Non-dairy fats and fat-filled milk powder (FFMP)
as fat sources: can be treated as analogues of AMF and WMP,

Figure 3.27:
Simplified mechanism for lipid oxidation. Many species, known as reactive oxygen species (ROS) and reactive
nitrogen species (RNS), may play a part in initiation.

Iron/Copper
Peroxides
ROS/RNS Unsaturated
1) Unsaturated lipids, Lipids (Milk fat Residual
2) Milk fat, 3) PUFA* PUFA) Oxygen

Nutrient losses

Peroxides Defects

Initiation Fuel Oxidant Off-flavours

Colour
change

Light Heat *Polyunsaturated fatty acid

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Recombining Milk
using ambient supply chains and (reactive) for protein degradation, PV may be used to budget
oxygen control. for fat degradation accumulation in both ingredients
• Non-dairy fats can also be frozen, analogous to and products.
FFMR. This is usually essential for specialty oils However, a budget for fat degradation in FFMP could
(e.g. algal DHA, fish oil). be quite complex considering the fat has primary
The chemistry of oxidation is complex, and space does (ingredient oil), secondary (FFMP) and tertiary
not permit discussion here. But monitoring (reactive) (beverage made from FFMP) shelf lives.
oxygen implies much more than controlling atmospheric Lipid peroxides do not have significant flavour. However,
oxygen by, for example, using inert gas for packing. Some they readily degrade to form off-flavours. The degradation
of the considerations include: of peroxides is accelerated by heat and transition metals
• Effects of intrinsic and added oxygen-scavenging (iron and copper). Therefore, it is plausible for ingredients
antioxidants (e.g. ascorbic acid). to taste acceptable yet to yield unacceptable products
due to the recombining process causing degradation of
• Effects of dissolved oxygen (removed by
peroxides. The widely-accepted solution to this problem
flash vessels).
across the fat industry is to use a diverse portfolio
• Effects of oxygen activation by iron and copper. of quality tests, e.g. PV, thiobarbituric acid reactive
• Effects of oxygen diffusion through substances (TBARS), AV and sensory, when accepting fats
packaging materials. and/or releasing finished goods. Appropriate specifications
are undoubtedly application specific.
Even though gas-flushed milk powder will contain
substantially more oxygen (because of low bulk density) Quality specifications for fats become particularly
than gas-flushed AMF, oxygen should be under enough complicated when fats are mixed and/or modified,
control (e.g. through intrinsic antioxidants) to achieve which is becoming more prevalent due to numerous fat-
stability comparable with AMF. related trends (keto diets, rejection of hydrogenated oils,
demand for PUFA etc.). From a nutritional perspective a
Consequences of oxidation reactions recombined formulation will be targeting a specific fatty
The consequences of oxidation in recombining can be acid composition (percentage of saturated fatty acids,
understood through the mechanisms of oxidation (see polyunsaturated fatty acids, ketogenic fatty acids etc.)
Figure 3.27). but there are at least three ways the same fatty acid
proportions can be achieved:
Lipid peroxides, measured as a peroxide value (PV), are
an important product of oxidation. PVs are commonly • Using fats containing interesterified fatty acids.
used as a recognised measurement of the quality of • Using fat blends (e.g. AMF and DHA algal oil) that
fat products. For instance, Codex suggests a maximum are emulsified with milk solids in one step.
of 0.3 and 0.6 mmol/kg fat for AMF and milk fat, • Using different fat sources (e.g. whole milk and DHA
respectively. In the absence of Codex suggesting a algal oil) that are introduced into a product in more
maximum PV for recombined cream, a high PV in than one processing step.
recombined cream could be taken to infer the cream
was made from poor-quality AMF. But a high PV in Each of the above leads to different emulsion structures
recombined cream is equally likely to be due to the and therefore different results with respect to fat
accumulation of oxidation during storage of both cream stability and other fat attributes, including colour. In each
and its ingredient, AMF. Like using furosine to budget case the relationship between chemical measures of fat
quality (e.g. PV) and sensory attributes will be different.

67
3.
Recombining
Milk

For instance, if DHA algal oil is emulsified with whole of oxidation is that dilution is a poor strategy to deal
milk a measurement of whole milk PV is unlikely to be with fat ingredients approaching or exceeding quality
related to DHA fishy flavour because the PV measures limits for lipid oxidation. For example, should a drum of
peroxides from both milk fat globules and DHA droplets. AMF or pallet of WMP be found near end of shelf life
Yet the only elements determining fishy flavour are the (e.g. due to inventory error) it may be tempting to dilute
DHA droplets. it with fresher products in order to use. This creates
two risks:
The summary conclusion is that recombining gives
options not normally available when using fresh milk. In • The old material has accumulated significant
particular, it gives options to blend or modify fats. These amounts of initiators of oxidation (e.g. peroxides)
options have both advantages and disadvantages with which initiate oxidation in the new material.
respect to product stability and other features that are • The old material has started to exponentially
application dependent. It is up to the product developer produce off-flavours; this means that any
to explore these options as they see fit. improvement from dilution is rapidly undone.
An implication that comes from studying the mechanism

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 3
EXPERT TIP:
Use fats from reliable suppliers who
handle it with care.

Recombining Milk
This is because it is too difficult to
judge the state of a fat through
testing alone.

So, dilution can make a small problem into a large one. appears to change is referred to as the induction period.
It is probably better to write-off a small amount of During this period it is seldom possible to measure
old ingredient than to risk needing to write-off large reaction rates to predict how much longer a material
amounts of finished product. may last, in the way that could be done for browning
reactions. After the induction period, reaction rates can
Characteristics of oxidation reactions be measured, but unfortunately in many cases the end
Unlike browning, oxidation is usually not a zero-order of the induction period is essentially where oxidation may
reaction. Oxidation sometimes appears to be zero-order become unacceptable.
creating some conflicting information in literature. This The inability to measure oxidative stability during
happens when the reaction hasn’t proceeded sufficiently the induction period creates an obvious problem for
for the reaction order to be clear. For practical reasons, recombiners using any fat source. There is no way to
it is best, when recombining, to assume that oxidation judge, by testing the fat, how far through its shelf
reactions exhibit the behaviour illustrated in Figure 3.26. life it is and how much time is left on the clock. This
As shown in Figure 3.26, oxidation rates are initially very problem is not unique to recombining and applies
slow. In fact, oxidation can proceed so slowly that no to any food formulated with fats and oils. Various
changes are measurable in the material being followed; attempts have been made to solve this problem (e.g.
that is until a critical point is reached where the rate of the Rancimat method) but there is little evidence that
oxidation rapidly accelerates. The period where nothing fat stability is predictable through testing and it is
certainly much less predictable than browning in protein.

69
3. EXPERT TIP:
Do not rely on heat to deactivate lipases.

Recombining
Because lipase can survive extreme
heat treatments it is better if they are

Milk
not present in the first place.

Also, it is much more difficult to determine how the 3.4.10

accumulated fat oxidation compares to the allowable
limit of fat oxidation when the accumulated oxidation
Fat degradation: lipolysis
is not measurable. Lipolysis is the reaction of lipids (fats and oils) with water
Because of the difficulties in judging the state of a fat to form free fatty acids that create severe off-flavours.
through testing alone, it is necessary to use fats from The requirement for water means that lipolysis does
reliable suppliers who handle fat with appropriate care not occur at a significant rate in powdered ingredients
and carefully document how it is handled. For instance, or anhydrous fat products (AMF and FFMR). Therefore,
steps taken to protect fat should be checked to confirm lipolysis does not play a role in primary (ingredient) shelf
they are in place. life but can determine secondary (product) shelf life.

One critical step to protect fat is modified atmosphere In acidic and neutral recombined products, lipolysis
packaging (MAP), as used for AMF, WMP and some should proceed at a negligible rate, such that it does not
non-dairy fats and oils (e.g. DHA). These products limit shelf life. However, should a recombined product
are packaged in an inert atmosphere containing low contain an appropriate catalyst (such as an enzyme),
amounts of residual oxygen (RO). Typically, the food lipolysis can occur at a rate that limits shelf life, if not
industry targets an RO < 2% to slow, but not stop, substantially shortens it. Enzymes of concern include
oxidation. Using an RO meter, it is possible to check if lipases, phospholipases and esterases. In pasteurised
this target has been achieved or not. Ideally the RO recombined products, such enzymes are produced by
should be below 2%, which is an order of magnitude microbial growth. In sterile products such as UHT and
less than a standard atmosphere. In milk powders, often retort, however, enzymes from ingredients used for
the RO won’t be below 2% but it has been shown that recombining can also cause problems if they survive
MAP has the same benefits at ROs as high as 4%. The the heat treatment of sterilisation. Such heat-stable
target RO of < 2% represents a margin of safety with enzymes occur surprisingly frequently in the dairy
there being room for higher ROs without necessarily industry, evident through substantial literature on the
causing problems. subject (Chen et al., 2003).

One of the reasons why an RO of < 2% should not be Normally ingredients used for recombining will not
considered a strict target is that RO represents many contain heat-stable enzymes. If they frequently did,
convoluted variables related to packaging and ingredient the current recombining industry would not be viable.
oxidation. For instance, a low RO could infer that an However, on rare occasions enzymes can be present in
ingredient has removed oxygen by being oxidised, which ingredients and cause poor stability and this cannot be
would be undesirable. However, a high RO might infer known in advance from the state of the powder, where
oxygen is not reacting, and oxygen that may have been the enzyme is inactive. In cases where enzymes cause
dissolved in the ingredient has come out of solution to problems it is therefore critical to be able to identify the
indicate a benefit. effected materials, so those materials are no longer
used. For instance, for a product recombined from SMP
and WMP it would be important to know which powder
was the source of the problem. To allow this, it is prudent
to keep retention samples either by the ingredient
manufacturer or recombiner or both. It is emphasised
that lipase enzymes that degrade recombined fats are
not necessarily coming from the fat source itself. Lipases
can be found in SMP and in protein products, where
they would not pose an issue unless recombined with

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Recombining Milk
fats and water. Again, this is very rare and is discussed Most assays do not work because they lack the
primarily for the purposes of troubleshooting and sensitivity required to measure changes in minutes
risk management. or hours that normally occur in weeks or months. In
contrast, highly sensitive assays can be prone to false
Although lipase is rare, recombiners should be aware of
positives, making them unsuitable for preventative
the risks and how to best manage them. Some critical
testing but an option for troubleshooting.
considerations are:
In addition, even when it is possible to measure enzymes
• Heat treatments applied during recombining
in powders, the measurement would not be predictive
can decrease, but not eliminate, risks of lipase by
of enzyme activity in recombined products, because the
deactivating enzymes.
activity in recombined products would depend on the
• The activity of lipase enzymes depends on the formulation and how it was heat treated. Therefore, it is
nature of the interfacial fat in the formulation. not possible to work back from the maximum acceptable
Therefore, significant changes to a formulation, amount of lipase activity in a beverage to the maximum
e.g. to change fat stability, can change susceptibility acceptable amount in a powder for every possible situation.
to lipases.
The types of off-flavours that form due to lipolysis
•
depend on the fat that is being used. Consequently,
3.4.12
changes to the type of fat being used can change Miscellaneous off-flavours in
susceptibility to lipolysis. recombined dairy products
• Because of the complexity of interfacial enzyme
Off-flavours are defined as flavours that form through
kinetics, the response of a lipolytic defect to enzyme
the expected degradation of food components such as
concentration is not linear. Similar to proteolysis,
proteins (proteolysis, browning reactions), fats (lipolysis
this can mean that a small decrease in enzyme
and oxidation) and carbohydrates (browning reactions).
concentration may give a surprisingly positive
We have covered the main components of dairy products
improvement, whereas a small increase may make
and the main off-flavours. However, there are some
the problem disproportionately worse.
minor components in recombined dairy products that
• There are assays that can be used to diagnose and can also cause off-flavours. While such issues are rare,
troubleshoot lipase issues, but these are seldom they can have high impact, especially for formulators
suitable for preventative purposes. that are unaware of where the boundaries lie.

3.4.11 Conjugated indoles and cresols

Viability of testing for lipases and Milk contains numerous minor components produced
other hydrolytic enzymes in powders through the normal biology of healthy cows. Among
used for recombining these components is a group of compounds known
as conjugated indoles and cresols. They are normally
The previous section begs the question: if there is a harmless and go unnoticed. However, under the right
risk of powdered ingredients containing enzymes, conditions the conjugates can be hydrolysed to form free
why not mitigate the risk by testing for enzymes? This indoles and cresols (including methylindole, i.e. skatole).
question has been posed widely across the dairy science The flavours formed can either be described as burnt/
community and the consensus is that there are very few, smoky or animal/stock truck. The flavours are released
if any, assays suitable for such testing. by heating milk solids in acidic solutions (pH < 3) or
by specific enzymes (aryl sulphatases). The enzymes

71
3.
Recombining
Milk

that release such off-flavours might inadvertently be

introduced when adding other enzymes such as lactase.
Indeed, lactase enzyme suppliers will often specify that
their products are free of aryl sulphatase.
The response to this type of off-flavour should be to
identify whatever is releasing the flavours from the
conjugates and prevent the release, because such
conjugates will always be present in large excess in
normal milk from healthy cows and the powders made
from it.

Off-flavours from instability during

fortification
Some nutrients form off-flavours when they degrade.
In fact, the formation of off-flavours as a result of
nutrient degradation can have an impact before
the loss of nutrition due to degradation becomes an
issue. This is particularly so for oils added as a source
of polyunsaturated fatty acids (e.g. DHA, ARA and
EPA) such as algal oils, fish oils and seed oils. Fish
and algal oils can produce fishy off-flavours. Other
oils can produce tallow and mushroom flavours. To
prevent such issues strategies must minimise oxidation.
Considerations in section 3.4.9 should be applied, as
well as recommendations from oil suppliers which may
extend to using additional antioxidants to achieve a
desired shelf life.
Other nutrients that have associations with off-flavour
formation include iron, vitamin A, vitamin C and some
of the B vitamins. Free amino acids can be problematic
also. This is actually an area of vast scope and therefore
the intention is only to indicate that when off-flavours
form in recombined products a systematic approach
and expert knowledge might be required to identify
the source.

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EXPERT TIP:
Nutrient losses are not always
due to degradation.

Recombining Milk
Losses can also be caused by
sampling and analysis issues,
losses in processing, or even
issues as a result of the nutrient
not being added.

3.4.13
Nutrient stability as part of ‘truth
in labelling’
When a product is sold for sensory reasons, consumers
are in a position where they can easily confirm, by
tasting, if their sensory needs are met. If expectations
are not met, they simply do not repeat the purchase.
In contrast, consumers have no means to confirm that
a nutritional claim is true. Instead, they must trust the
food industry and those who police it, such as regulators,
academics and consumer groups. These groups enforce
nutritional claims by comparing the results of chemical
analyses to what is claimed.
If a claim is based on knowing exactly how much
ingredient was added to a food during manufacture, the
claim will only appear 100% true, by chemical analysis,
provided that:
• Ingredient suppliers have correctly stated nutrient
contents (or the purity is 100%).
• Natural variations in nutrient contents are The above problems manifest themselves when label
accounted for. claims are based on the inherent nutrient content of
• Ingredients, fortificants and water are dairy ingredients used for recombining, or the addition
accurately measured. of nutrients through non-dairy ingredients including
• No nutrient is lost during processing for physical highly purified fortificants. Often, a nutritional claim on
reasons (e.g. spills or sediment). a recombined product may be based on contributions
from dairy ingredients and other sources. For instance,
• No nutrient is lost during processing due to
calcium might be present from milk powders and added
chemical reaction.
calcium salts.
• No nutrient is lost during storage for
chemical reasons. Control of such factors to achieve an evidentially truthful
label is well beyond the scope of this manual. For every
• The nutrient is homogenously distributed
formulation, and market, the problems are different
between packages.
and can include issues related to regulations, stability,
• Sampling of the packages is representative. compatibility, sampling, analysis and statistics. But a few
• Analyses are sufficiently accurate. generalisations provide a starting point.
The above will seldom be true. Therefore, some tolerance The inherent nutrition delivered through dairy ingredients
occurs on the testing side (the test result might need to (see Chapter 10, Nutrition) is relatively storage stable.
fall below 80% of the claimed amount before a problem However, as a natural product, the nutrient content
is flagged) and on the production side (more nutrient of dairy ingredients can still be uncertain and exhibit
than claimed is added – so-called overage). variability due to biological (often seasonal) and

73
 Table 3.6:
Common nutrients and their stability considerations.

Nutrient Comments Susceptible to Formulation

Fat-soluble nutrients
Vitamin A Beware of upper limit Oxidation • Fat-soluble nutrients
(light, oxygen, pro-oxidants, are compatible with
iron, copper, peroxides) each other.
Vitamin D Beware of upper limit Physical separation (creaming • Fat-soluble nutrients work
can lead to apparent loss best in presence of fat.
if cream is not represented
Vitamin E during analytical sampling) • Physical stability important.

Vitamin K Beware of upper limit

Lutein & Carotene Coloured!

PUFA (e.g. DHA, ARA, EPA) Risk of off-flavours

Water-soluble vitamins
Niacin (B3)

Pantothenic acid (B5)

Minimal issues
Pyridoxal (B6)

Folate (B9)

Riboflavin (B2) Photo-activator Light is a severe risk! Avoid light

Thiamine (B1) Off-flavours Light and heat

Cobalamin (B12) Difficult Light reductants • Minimise excess

Light-sensitive (vitamin C, antioxidants, antioxidants.
cysteine, polyphenols)
Vitamin C Large overages common Oxidation • Losses due to oxygen
(ascorbic acid) but can cause problems (light, oxygen, pro-oxidants, can be calculated (1 mg
iron, copper, peroxides) oxygen reacts with 11 mg
ascorbic acid).

Minerals
Iron Difficult but not impossible Physical (apparent) loss due • Promotes oxidation so can
to insolubility and sediment be very difficult to use.

Calcium & Magnesium Soluble forms ‘gel’ proteins • Avoid soluble forms.

Miscellaneous nutrients
Soluble fibre Few issues if fully solubilised
(e.g. GOS, FOS, Inulin)

Phytonutrients Can impact flavour and Diverse chemistry Specialised

(e.g. polyphenols) functionality

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3.
Recombining

Recombining Milk
Milk

processing variability, sampling and analysis. Care should 3.4.14

be taken when reviewing documentation to distinguish
between values reported as minimum, maximum,
Options to improve nutrient
typical and actual. Where actual values are reported fortification for recombined products
an understanding of errors in sampling and analysis
The motivation to fortify is the same in recombined
is required to appreciate implications for testing of
products as for fresh milk products. Likewise, in general
recombined products made from the ingredient. Truth
the approach to fortification and achieving sufficient
in labelling is determined both by nutrient stability
stability should be the same. Therefore, in the first
and these other sources of variability; so, you should
instance proven strategies from literature or suppliers
be careful not to jump to conclusions if results are not
should be followed and verified with suitable trials.
as expected.
However, recombining does provide some options that
Most nutrients for fortifying are relatively stable in might not otherwise be available when using fresh
pure form on their own. They become unstable when milk. For instance, fat-soluble nutrients (e.g. DHA, oily
they are not compatible with something else. A well- vitamins A, D and E) could be dissolved into milk fat
known nutrient supplier makes the point that many (AMF or FFMR) before recombining. At a minimum,
of their nutrients are not compatible with water, and this would help achieve very homogenous nutrient
therefore recombining. That point is based on Figure distribution but the effect on stability would need to be
3.23 from section 3.4.1 earlier in this chapter. However, determined through appropriate trials.
a survey of the market will find products containing
Fat-soluble vitamins such as A, D and E are most
just about every combination of nutrients imaginable
commonly sold as ‘cold-water soluble’ (CWS) powders
in products that contain water and oxygen. This occurs
for direct addition to water (e.g. beverages, yoghurts)
because compatibility and stability are relative terms
and these are a good option for either fresh or
and what is considered acceptable depends on the
recombined products. The technology used to make a
situation. So, in Table 3.6 we provide some suggestions
fat-soluble vitamin water-soluble comes at a cost, so
on what combinations tend to be less compatible and
therefore less stable; however, that does not mean
such combinations should not be attempted. Food
manufacturers are expected to undertake sufficient
due diligence.
The apparent loss of a nutrient might not always be
attributed to poor stability caused by an incompatibility.
For instance, during sampling and analysis an emulsified
fat-soluble nutrient added to water can behave
differently from its oily equivalent added to fat. The
possibility of such issues should be considered and
where they are suspected, it is prudent to check whether
the analytical methods have ever been validated on a
recombined product.

75
3.
Recombining
Milk

these tend to be the most expensive way of adding fat- For highly-coloured nutrients, such as lutein and
soluble vitamins. But when recombining is being done the carotene, a further consideration when deciding between
alternative option of adding the raw fat-soluble vitamin using the oily form (added to fat) or CWS form (added
directly to the fat becomes available. This option for to water) is the colour of the product achieved compared
vitamins is commonly referred to as the ‘oily form’. It is to the colour desired. Our experience is that the way
likely a cheaper option because it is the raw ingredient in which the nutrient is added can have a large impact
without any supporting technology. on colour. Coloured nutrients added to fat can often
cause more colour than if the nutrients were added to
water, which may or may not be desired. However, when
recombining, at least the option to do either is available.

Table 3.7:
A summary of shelf life of UHT milks (M = months) based on the proteolytic activity of psychrotrophic
bacteria numbers at different temperatures.

Raw milk quality P. rhodesiae DZ351 P. synxantha DZ832 Mixed isolates

(numbers) 20°C 30°C 20°C 30°C 20°C 30°C

104 CFU mL-1 < 7 (M) <5 <6 <4 <6 <4

105 CFU mL-1 <6 <4 <5 <4 <5 <4

106 CFU mL-1 <5 <4 <6 <3 <6 <3

10 CFU mL
7 -1 <1 <1 <1 <1 <1 <1

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Recombining Milk
3.5 milk with active lipase. This is usually much less than
the time taken to pasteurise the batch of mixed milk.
Milk extension Pasteurisation (of the raw milk) after mixing with the
recombined milk will usually be too late as rancidity will
Where the fresh milk supply does not meet have already developed.
demand, it is common practice to supplement
it with recombined milk. The process is
3.5.2
fairly simple, but some precautions must Attack by bacterial proteases
be observed. Milk extension is also discussed Where it is necessary to supplement fresh milk with
in Chapter 9 – Cheese milk extension and recombined milk, handling small volumes of raw milk
recombined milk. correctly is often a problem. In such situations, milk
chilling during transport to the processing plant is
3.5.1 usually inadequate and high bacterial counts may be
Inactivation of the milk lipase in the found. When numbers of common psychrotrophic
fresh milk and mesophilic bacteria reach much over 106 CFU/
mL, significant amounts of protease may be released
Raw fresh milk contains an active lipase that will (Fairbairn & Law, 1986). These proteases are often heat
hydrolyse unprotected fat to give free fatty acids, resistant and survive heat-sterilisation treatment in a
creating a rancid taint. In unprocessed milk, the fat is UHT plant or even an autoclave. Subsequent protease
protected by an intact natural fat-globule membrane, attack on the milk protein can cause unacceptable
which cannot be penetrated by the milk lipase. If this sediment levels in the sterilised milk.
membrane is broken, by mishandling the milk or by It has been noted that this effect appears to be
homogenisation, the lipase can act on the exposed fat. influenced by the level of milk fat present. A recent
Even though a new surface membrane, composed of study has shown that milk fat in whole milk can trigger
milk proteins, coats the newly exposed fat surface in populations of Pseudomonas from raw milk to produce
homogenised milk, the milk lipase can penetrate the protease enzymes (Zhang et al., 2020a). Therefore, it is
new membrane and still attack the fat, and does so important that raw milk, to be mixed with recombined
very rapidly. However, the lipase is easily inactivated milk, is pasteurised without delay on receipt at the
by pasteurisation (Driessen, 1989). Therefore, it is processing plant. This will minimise the growth of
important that the lipase is inactivated by a heat psychrotrophic bacteria present, which will reduce the
treatment, at least equivalent to pasteurisation, when risk of heat-stable protease enzyme production.
the milk is homogenised.
The shelf life of UHT milk can be influenced by the
The same principle applies when fresh milk is mixed numbers and types of Pseudomonas spp. present in the
with recombined milk. If the fresh milk contains active raw milk. For example, a recent study by Zhang et al.
milk lipase, it will immediately attack the fat in the (2020b) showed that if P. rhodesiae were present at 104
recombined milk, despite the milk-protein membrane CFU/mL in the raw milk, the UHT product would have
around the fat. So, it is essential to ensure that the a likely shelf life of about 7 months (20°C). P. synxantha
lipase in the fresh milk is inactivated, by pasteurisation, at the same level resulted in an estimated shelf life of
before mixing it with the recombined milk. It may take 6 months (see Table 3.7).
as little as 30 min to develop lipolytic rancidity in mixed

77
References

1. Atiemo-Obeng, V. A. & Calabrese, R. V. (2004). Rotor 9. Karbstein, H. & Schubert, H. (1995). Developments
stator mixing devices. Handbook of Industrial Mixing: in the continuous mechanical production of oil-in-
Science and Practice, 479–505, Hoboken, NJ, USA. water macro-emulsions. Chemical Engineering and
John Wiley & Sons, Inc. Processing: Process Intensification, 34(3), 205–211.
doi.org/10.1016/0255-2701(94)04005-2
2. Chen, L., Daniel, R. M. & Coolbear, T. (2003). Detection
and impact of protease and lipase activities in milk 10. Lloyd, M.A., Hess, S.J. & Drake, M.A. (2009). Effect of
and milk powders. International Dairy Journal, 13(4), nitrogen flushing and storage temperature on flavor
255–275. doi.org/10.1016/S0958-6946(02)00171-1 and shelf life of whole milk powder, Journal of Dairy
Science, 92(6), 2409–2422. doi.org/10.3168/jds.2008-
3. Driessen, F. M. (1989). Inactivation of lipases and
1714
proteinases (indigenous and bacterial). In Monograph
on Heat-induced Changes in Milk. IDF Bulletin 11. McKenna, A. B. (2000). Effect of processing and
Doc.238, 71–93. International Dairy Federation, storage on the reconstitution properties of whole
Brussels, Belgium. milk and ultrafiltered skim milk powders. Ph.D. thesis,
Massey University, Palmerston North, New Zealand.
4. Espinoza, C., Alberini, F., Mihailova, O., Kowalski, A.
Retrieved from http://hdl.handle.net/10179/4587
& Simmons, M. (2020). Flow, turbulence and
potential droplet break up mechanisms in an 12. MPI (2022), Chapter D of the Animal Product Notice:
in-line Silverson 150/250 high-shear mixer. Chemical Product, Supply and Processing. Part D3, subpart 4:
Engineering Science: X, 6, 100055. doi.org/10.1016/j. Defined heat treatments. Retrieved from https://
cesx.2020.100055 www.mpi.govt.nz/dmsdocument/50182-Animal-
Products-Notice-Production-Supply-and-Processing
5. Fairbairn. D.J. & Law, B. A. (1986). Proteinases of
psychrotrophic bacteria: their production, properties, 13. MPI (2019); Alkaline phosphatase – Guidance
effects and control. Journal of Dairy Research, document. Retrieved from https://www.
53, 139-177. mpi.govt.nz/dmsdocument/32668-Alkaline-
Phosphatase-Testing-Guidance
6. Favstova, V. (1962). Methods for reconstitution of
dried whole milk. Molochnaya Promyshlennost, 23(2), 14. Mulder, H. & Walstra, P. (1974). The Milk Fat Globule.
23–23 [Russian]; Dairy Science Abstracts, 24, 1582 Emulsion Science as Applied to Milk Products and
[English abstract]. Comparable Foods. Commonwealth Agricultural
Bureaux, Farnham Royal, Bucks, England.
7. Forny, L., Marabi, A. & Palzer, S. (2011). Wetting,
disintegration and dissolution of agglomerated 15. Newstead, D. F., Groube, G. F., Smith A. F. & Eiger,
water soluble powders. Powder Technology, 206(1–2), R. N. (1999). Fouling of UHT plants by recombined
72–78. doi.org/10.1016/j.powtec.2010.07.022 and fresh milk. Some effects of pre-heat treatment.
In Proceedings of a Conference Held at Jesus College,
8. Gibson, D. L. & Raithby, J. W. (1954). Studies on
Cambridge, 6–8 April 1998; Fouling and cleaning
improving the ease of reconstitution of skim milk
in food processing '98, D. I. Wilson, P. J. Fryer & A.
powder. Canadian Journal of Technology, 32(2),
P. M. Hastings (Eds). Doc. EUR 18804, European
60–67.
Commission (Brussels).

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16. Newton, A. E., Fairbanks, A. J., Golding, M., Andrewes, 23. Zhang, D., Li, S., Palmer, J., Teh, K. H., Leow, S. &
P. & Gerrard, J. A. (2012). The role of the Maillard Flint, S. (2020). The relationship between numbers
reaction in the formation of flavour compounds in of Pseudomonas bacteria in milk used to
dairy products – not only a deleterious reaction but manufacture UHT milk and the effect on product
also a rich source of flavour compounds. Food and quality. International Dairy Journal, Vol. 105, 104687.
Function, 3, 1231–1241. https://doi.org/10.1039/ doi.org/10.1016/j.idairyj.2020.104687
c2fo30089c
24. Zhang, J., Xu, S. & Li, W. (2012). High-shear mixers:
17. Norman, G. H. (1955). Dried buttermilk improves A review of typical applications and studies on power
palatability of reconstituted milk. Milk Products draw, flow pattern, energy dissipation and transfer
Journal, January 1955, 38–39. properties. Chemical Engineering and Processing:
Process Intensification, 57, 25–41. doi.org/10.1016/j.
18. Stoeckel, M., Lidolt, M., Stressler, T., Fischer, L.,
cep.2012.04.004
Wenning, M. & Hinrichs, J. (2016). Heat stability
of indigenous milk plasmin and proteases
from Pseudomonas: A challenge in the production
of ultra-high-temperature milk products.
International Dairy Journal, 61, 250–261.
doi.org/10.1016jidairyj.2016.06.009
19. Tetra Pak (2020). Dairy Processing Handbook. Tetra
Pak Processing Systems AB, Lund, Sweden. Retrieved
from https://dairyprocessinghandbook.tetrapak.com/
20. Utomo, A., Baker, M. & Pacek, A. (2009). The effect
of stator geometry on the flow pattern and energy
dissipation rate in a rotor-stator mixer. Chemical
Engineering Research and Design, 87(4), 533–542.
doi.org/10.1016/j.cherd.2008.12.011
21. Van Boekel, M. A. J. S. (2008), Kinetic modeling of
food quality: A critical review. Comprehensive reviews
in Food Science and Food Safety, 7, 144–158.
doi.org/10.1111/j.1541-4337.2007.00036.x
22. Zhang, D., Palmer, J., Teh, K.H., Calinisan, M.M.A.
& Flint, S. (2020). Milk fat influences proteolytic
enzyme activity of dairy Pseudomonas species.
International Journal of Food Microbiology, 320,
108543. doi.org/10.1016/j.ijfoodmicro.2020.108543

79
4.
Recombined
Milk – Normal
Concentration
This chapter outlines the processes
and ingredients used to make normal
concentration, recombined:
• Pasteurised milk.
• Extended-shelf-life (ESL) milk.
• UHT-sterilised milk.
• Retort-sterilised milk.

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Recombined Milk – Normal Concentration

4.
Recombined Milk –
Normal Concentration

4.1 Pasteurised milk contains some active

microorganisms
Introduction
Although vegetative (growing) pathogens are largely
We begin with a summary of the main eliminated by pasteurisation, pasteurised milk still
contains active microorganisms. These include:
similarities and differences of the above
products. Later sections address the • Thermoduric vegetative microorganisms and heat-
manufacturing process for each one. resistant spores that can survive pasteurisation.
• Psychrotrophic microorganisms that can
Fat-content classes contaminate milk post-pasteurisation, which
Whether it is pasteurised, UHT sterilised or retort will eventually lead to spoilage even at
sterilised, recombined milk (like fresh milk) is produced in refrigeration temperatures.
several fat-content classes. Precise definitions vary from
country to country, but in general they are:
UHT and retort sterilisation inactivate most
spoilage organisms
• ≥ 3.25% fat: whole milk or full-cream milk.
The process conditions normally applied during UHT
• ≤ 1.50% fat: reduced-fat milk.
processing and retort sterilisation are designed to give
• ≤ 0.50 % fat: low-fat milk. microbiologically stable products. They achieve this
Flavoured milks typically contain 2.0% fat and at least by largely inactivating microorganisms likely to cause
4.0% sugar (sucrose), as well as flavourings. spoilage under normal storage conditions (i.e. up to
40°C). It is possible that a very low level of highly heat-
Non-flavoured sweetened milk typically contains 8.0% resistant spores produced by specific strains of bacteria,
whole milk solids (including 2.2% fat) and 5% sugar. such as Geobacillus spp., could survive such treatments.
Distinguishing characteristics However, these will rarely germinate and grow to cause
spoilage. In fact, this spoilage is only significantly possible
The distinguishing characteristics of the various types when there is temperature abuse of the product.
of heat-preserved, unconcentrated milks are shown in
Table 4.1.

Table 4.1:
Comparison of heat-preserved, unconcentrated consumer milks.

Pasteurised milk Extended-shelf-life UHT-sterilised milk Retort-sterilised

(ESL) milk milk
Typical heating regime ≥ 72°C for ≥ 15 s 120°C to 130°C 140°C for 4 s 120°C for 10 min
(63°C for 30 min) for 2 s
Storage temperature < 5°C < 5°C ambient ambient
Typical shelf life 14 days 4–6 weeks 3–9 months 1 year
Flavour fresh less ‘cooked’ than slightly ’cooked’ ’cooked’
UHT milk

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Recombined Milk – Normal Concentration

Figure 4.1a:
Comparison of typical temperature–time profiles for pasteurisation, direct-steam-heating UHT processing,
indirect-heating UHT processing and retort sterilisation. See Figure 4.1b for an expanded view of the
temperature–time profiles for direct and indirect UHT.

160
Pasteurisation
140 UHT (direct)
UHT (indirect)
120 Retort
Temperature (°C)

sterilisation
100

80

60

40

20

0
0 3 0 3 0 3 0 5 10 15 20 25 30
Time (min)

Figure 4.1b: The main differences between UHT and

Time–temperature curve for UHT treatment in direct A retort sterilisation
and indirect B system.
UHT-sterilised milk and retort-sterilised milk have
150 different heat processes and packaging methods. UHT
A
sterilisation is a continuous-flow process followed by
B
aseptic packaging into pre-sterilised containers. The
retort-sterilised product is pre-packed, sealed into the
final container and batch-sterilised. The contrasting
100
heat-treatment profiles involved in their production are
Temperature °C

shown in Figure 4.1a.

50

0
20 40 60 80 100 120
Time (s)

83
4.
Recombined Milk –
Normal Concentration

4.2 Pasteurisation
Pasteurised milk – For effective pasteurisation:

normal concentration • The temperature sensors and regulators

in the pasteuriser should be checked and
As mentioned above, pasteurisation is designed to calibrated regularly.
prolong the shelf life of milk kept under refrigeration. • The holding section must be properly suited to the
It does this by eliminating pathogenic microorganisms milk flow (which should be regulated) so that no
from the milk and most psychrotrophic spoilage portion of the milk passes through in less than the
organisms, capable of growing at < 7°C. minimum regulation holding time.
When pasteurisation conditions are not achieved, e.g. if
4.2.1 the pasteurisation temperature drops below the required
Processing temperature, a flow diversion valve opens–diverting
unpasteurised milk back to a raw milk balance tank.
The requirements for good-quality pasteurised
recombined milk production are no different from Avoiding recontamination
those for fresh milk.
• Cleaning and sanitising the plant effectively,
particularly all sections after the pasteuriser
Homogenisation
holding pipe.
Homogenisation should be placed before the • Ensuring there are no leaks or cracks in the pipework
pasteurisation step. This is to avoid the high probability or heat exchanger.
of milk recontamination as it passes through the
• Designing the regenerative sections of heat
homogeniser. Homogenisers are common sources of
exchangers so that, if a crack does occur,
microbial contamination because they are difficult to
no unpasteurised milk can flow through to
clean and sanitise effectively. Adequate cleanliness
recontaminate the already pasteurised milk.
is seldom achieved reliably by simple clean-in-place
regimes. In a well-run plant, particular attention is paid
Chilling
to homogeniser maintenance and cleaning. Specifically,
the plungers, seals and homogeniser head should be The milk must be immediately chilled to ≤ 10 °C
inspected and hand-cleaned at regular intervals. (preferably ≤ 7°C).

Because there is little risk of significant cream layer Filling

formation during the relatively short shelf life of
pasteurised milk, high homogenisation pressures are not The packaging equipment, the packaging
required. Typically, pressures in the range of 100 to 150 material (bottles or cartons) and the filling room
bar (total for a two-stage process) would be adequate. environment must be hygienic, with very low levels of
The fat-globule size distribution should be such that contaminant organisms (see Chapter 2, section 2.2.3,
> 95% of fat globules are < 2 µm (volume distribution). Environmental monitoring).
This can be easily checked using a microscope.

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Recombined Milk – Normal Concentration

Keeping the milk chilled
Figure 4.2:
After packaging, the ‘cold chain’ from factory to Pasteurised recombined milk.
consumer must be maintained. During the entire period
of its shelf life, pasteurised milk should be kept below
Hydrate WMP in Hydrate SMP in
5°C. If these conditions are met, pasteurised milk should water at 40°C–55°C water at 40°C–55°C
have a shelf life of 14 days or more. However, if the cold
chain is broken (i.e. temperature cycling or a temperature
spike), it pays to be aware of the risks, such as spoilage Add melted fat (at
occurring before the end of shelf life. approximately 60°C)
with agitation to form
An alternative process – pasteurisation primary emulsion
in bottles
Pasteurisation can also be carried out in a water
bath with the milk packaged in filled and sealed bottles
Filter (100 μm)
or pouches.
Short holding treatments are clearly not possible for
this process. For a suitable long-hold heat treatment, Deaerate (optional)
minimum pasteurisation requirements (for milk) are
63°C for 30 min.
Homogenise 70°C–75°C
In this process, it is essential that the bottles or pouches:
100–150 bar (total)
• Are totally immersed in the hot water; otherwise
the head-space in the top of the bottle will not be Pasteurise
sufficiently heated and will remain contaminated. ≥ 72°C for ≥ 15 s
• Are tightly, or ideally hermetically, sealed; otherwise
they may be recontaminated by air and condensate
Chill to ≤ 8°C
can be sucked in through the leaky seal as the milk (preferably ≤ 7°C)
shrinks on cooling.
• Have reached 63°C (internal temperature) before
the 30 min timing begins; this can be monitored Fill bottles/cartons
by placing a filled pilot bottle with a calibrated
temperature probe in the middle of the bath during
Check microbiological quality
each pasteurisation treatment.
(APC and coliforms)
Summary of pasteurised milk production
from reconstituted milk Maintain < 5°C cold chain
throughout distribution
A schematic flow diagram for the production of
pasteurised milk, from reconstituted whole milk powder
(WMP) and from recombined skim milk powder (SMP) (Recall unsold stock at
end of shelf life)
and fat, is shown in Figure 4.2.

85
 EXPERT TIP:
Contamination of pasteurised
milk occurs most commonly
after the pasteurisation step,
or due to a breakdown in the
cold distribution chain.
With its short shelf life,
functional problems, such as
cream layering, are very rare.

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4.
Recombined Milk –

Recombined Milk – Normal Concentration

Normal Concentration

4.2.2 Packing

Ingredient milk powder To take best advantage of the ESL concept, the milk
should be aseptically packed (as for UHT milk) or, at the
The type of milk powder used for pasteurised very least, packed into near-sterile containers under
recombined milk is not critical, as far as recombining conditions of extremely high hygiene.
and processing are concerned. However, if it is desired
to minimise the ‘cooked’ flavour characteristic of heated Keeping ESL milk chilled
milk, a milk powder of low-medium heat to low heat is The cold chain must also be very closely controlled also.
recommended and the pasteurisation heat treatment The time for which the milk temperature is allowed to
should be kept near the minimum. If the ’cooked’ flavour rise above 4°C must be kept to the absolute minimum
is desired, then either a higher-heat milk powder can to reduce spoilage risks. These include sedimentation,
be selected or the pasteurisation heat treatment can curdling, separation and off-flavours that may be
be increased. associated with growth and enzyme production by
Pasteurised milk can also be made from frozen milk surviving organisms.
concentrate (see Chapter 2 and Chapter 7 for details). The following illustrates the hazards of not meeting
these conditions.

4.3 A single bacterium can spoil milk in five days

Extended-shelf-life (ESL) milk At a temperature of only 6°C, the generation time for

– normal concentration common psychrotrophic bacteria, such as Pseudomonas

spp. and Enterobacter cloacae, is 5 h (Renner, 1985). At
this growth rate, a single contaminating organism in a
In practical terms, ESL milk (sometimes carton of milk could reach spoilage levels, defined as 106
called high-pasteurised or ultra-pasteurised bacteria/mL (Doll et al., 2017), in 5 days.
milk) is similar to pasteurised milk. However,
if properly managed, it may have two to three Common spore-forming bacteria can
times the shelf life. cause spoilage as well
Paenibacillus spp. are common spoilage spore-forming
Heat treatment bacteria of pasteurised and ESL milks. They have a wide
The ESL process applies a heat treatment that is temperature growth range (between approximately 5°C
significantly less than full sterilisation but greater than and 55°C) (Deeth, 2017). These bacteria have recorded
normal pasteurisation (e.g. 120°C to 130°C for 2 s, growth rates in skim milk broth at 6°C of between 0.6
140°C for 0.5 s). This makes it possible to obtain milk and 1.5 log10 CFU/mL per day.
with a lesser ‘cooked’ flavour than UHT-sterilised
Similarly, other spore-formers, such as B. weidmanii and
milk and a longer shelf life under refrigeration than
B. weihenstephanensis, have recorded growth rates of 1
pasteurised milk. The heat treatment is chosen to
to 1.5 log10 CFU/mL per day at 6°C (Buehler et al., 2018).
inactivate all the vegetative (growing) bacteria and
most (but not all) of the bacterial spores. The extra Therefore, the heat treatment used must be sufficient
heat treatment used for actual sterilisation is required to kill these types of spore and there must be no
only to kill the most heat-resistant spores. recontamination of the milk after heat treatment or
during the filling operation.

87
4. EXPERT TIP:
Do not rely on UHT heat treatment

Recombined Milk –
to inactivate microbial enzymes.
See lipase and protease in Figure 4.3.

Normal Concentration

4.3.1 Heat treatments with an F0 of 3 min

Ingredient milk powder It is widely accepted in the food industry that a heat
treatment with an F0 of 3 min is adequate to produce
The ingredient requirements for ESL recombined milk commercially sterile foods, with a near-neutral pH
are the same as for pasteurised recombined milk (see (> 4.6), when stored at ambient temperatures.
section 4.2.2).
The meaning and relevance of an F0 of 3 min
4.4 The F0 of 3 min originates from the canning industry,

UHT-sterilised milk –
where it is historically and widely accepted that >
12-log reduction of Clostridium botulinum spores is an
normal concentration adequate level of risk. To achieve this reduction, canned
foods are typically heated to 121.1°C and held for 3 min.
UHT milk is now the predominant form of C. botulinum spores have an average death rate (or D
value) at 121.1°C of 0.19 min (Diao et al., 2014) (so,
unconcentrated milk in the recombined milk
for every 0.19 min at 121.1°C there is one log reduction
market. However, both of the traditional of spores). Consequently, if food is held at 121.1°C
recombined concentrated milks, recombined for 3 min, there is a theoretical 15-log reduction of C.
evaporated milk (REM) and recombined botulinum spores (3 min / 0.19 min per log reduction).
sweetened condensed milk (RSCM), are still
produced in greater quantities. Higher temperatures can achieve the same F0 value in
less time.

4.4.1 In the dairy industry, UHT beverages are typically

heated at 140°C to 145°C for 4 to 6 s. The increased
Key characteristics of the UHT process temperature and decreased time prevents nutrient
The UHT process takes advantage of the following degradation, preserves the quality and sensory
fact. As the milk temperature is increased, the rates characteristics of the formulation, and increases the
of bacteria and bacterial spore destruction increase energy efficiency of the process.
faster than the rates of the chemical processes for
Calculating F0 for temperature and heating
key nutrient degradation, flavour deterioration and
time combinations
browning. Therefore, by increasing the temperature,
the time required for sterilisation can be reduced until The average z value for C. botulinum spores is 11.3°C;
the nutrients in the milk are not significantly affected, however it is historically regarded as 10°C (Diao et al.,
the flavour is affected only a little and there is no 2014). Therefore, for every 10°C increase in temperature
browning at all. above 121.1°C, the death rate (D value) of C. botulinum
spores increases by a factor of 10. When heat treatment
As a result, compared with retort-sterilised milk, UHT- temperatures of > 121.1°C are used, the following
sterilised milk has much less ‘cooked’ or caramelised equation can be used to calculate the F0 of the heat
flavour, no visible browning and negligible loss of heat- treatment relative to a heat treatment temperature of
sensitive nutrients. These points are well illustrated in 121.1°C:
the diagram (Kessler, 1981) reproduced in Figure 4.3. T-121.1°C
F0 = t x 10 10°C
60

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 4
EXPERT TIP:
Allow for a safety and quality
margin in your UHT heat treatment.
Higher levels of heat treatment are

Recombined Milk – Normal Concentration

used to ensure adequate thermophile
spore kill. Surviving thermophiles
can grow in ambient-stored product
and cause spoilage. We recommend
operating UHT within a narrow range
of high temperatures for a short time
(usually 140°C–145°C for 4–6 s), to
kill any highly heat-resistant spores
present, while minimising nutrient
degradation (see Figure 4.3).

where t = heat treatment time in seconds, T = heat C. botulinum spores is achieved (5.2 / 0.19 = 27)).
treatment temperature (°C) and the z term has been When the heat treatment time is 4 s, the minimum
set as 10°C. temperature to achieve an F0 of 3 is 137.6°C.
Temperatures of 140°C to 145°C are typically used to
If the above F0 equation shows that an F0 of > 3 is
build in a safety margin for when the flow rate may
achieved by a heat treatment with a given temperature
surge (and therefore decrease the heat treatment time
and time, then it can be demonstrated that the heat
in the holding tube), or for when the temperature may
treatment is adequate to achieve a > 12-log reduction of
decrease (e.g. due to a sudden pressure drop in the
C. botulinum spores and therefore has an adequate level
holding tube). These have an increased risk of occurring
of food safety risk.
early in the process when switching from water to
product. In New Zealand, regulators (MPI) require a
Allowing for a safety margin
minimum F0 of 3 over the heat treatment holding tube
A heat treatment of 140°C for 4 s has an F0 of 5.2
simultaneously at both the max/divert flow rate and
(consequently a theoretical 27-log reduction of
min/divert temperature. Under steady state an F0 of

Figure 4.3:
Limiting lines for the heat destruction of bacterial spores and effects of heat on
the constituents of whole milk (Kessler, 1981).

Region of in-container sterilisation

Heating Time or Equivalent Heating Time, s

2000
90%
1000 Ps-l
ipas
600 e ina
3% D No d ctiva
400 estru 9 isco tion
ction 0% Ps-pr lou r
200 of th oteas ation
iami e inac
ne tivatio
100 1% D n
estru
60 ction
Destruction of spores of lys
40 ine
Logarithmic death value = 9
20
Mesophilic spores (30°C)
10
Thermophilic spores (55°C)
6 UHT region
4
2
1
110 120 130 140 150
Temperature (°C)

89
4.
Recombined Milk –
Normal Concentration

much greater than 3 is often achieved. It can be in and this is assuming an average heat sensitivity (i.e. D
excess of 30, particularly when using indirect heating value). Some strains can have higher D values (the Q0.975
and taking into account the heat treatment that occurs D value is 9.6 min at 121.1°C for G. stearothermophilus
during heating from 121°C to the target temperature of spores) (Rigaux et al., 2013). The adequate level
approximately 140°C in the holding tube. of risk can depend on a range of factors. Here are
some examples.
Why C. botulinum is the benchmark organism
The composition of species and strains of thermophilic
C. botulinum and botulism illness is used as the
spores present in the food
benchmark organism for the design of heat treatments
for ambient stable, near-neutral pH foods. This is • Geobacillus spores are more heat resistant than
because it is a pathogen and causes disease of the Anoxybacillus spores and G. stearothermophilus
greatest severity. Other mesophilic pathogens, such spores have a relatively high heat resistance
as B. cereus spores, have comparable heat sensitivity compared to the spores of other Geobacillus species.
to C. botulinum. Therefore, if C. botulinum spores are
The product storage temperature during its shelf life
adequately inactivated with a > 12-log reduction, the
spores of other mesophilic pathogens and spoilage • Geobacillus species have a minimum growth
organisms are likely to be adequately controlled, also. temperature of 35°C and Anoxybacillus species
have a minimum growth temperature of 30°C
Managing thermophilic spore levels (Burgess et al., 2010).

Thermophilic spores can cause quality defects in UHT • If the storage temperature is maintained
product, referred to as a flat-sour sensory defect (where below 30°C to 37°C, the risk of spoilage due to
the bacteria produce acid but no gas, so the packaging thermophilic spore germination and growth is
appears normal i.e. ʻflatʼ, and does not appear bulged); greatly decreased.
however, they are not pathogenic and do not cause
illness. Thermophilic spores, such as those belonging The number of thermophilic spores in food before
heat treatment
to the Geobacillus genus, have a relatively high heat
resistance and the greatest chance of surviving UHT • The lower the number of spores present
heat treatment. Geobacillus stearothermophilus has (particularly Geobacillus spores), the lower the
a particularly high heat resistance compared to other risk of product spoilage.
Geobacillus species, and has an average D value at
121.1°C of 3.3 min at a pH of 7 (Rigaux et al., 2013).
Therefore, for every 3.3 min at 121.1°C, or for every F0
of 3.3, theoretically there is one log reduction of
G. stearothermophilus spores.
Adequate levels of risk
There is a range of reported adequate levels of risk
for the log reduction of thermophilic spores by heat
treatment for ambient stable, near-neutral foods, with
a required 2-to 9-log10 reduction reported.
To achieve a 2-log10 reduction of G. stearothermophilus
spores, an F0 of 6.6 (2 x 3.3) would be required. For a
9-log10 reduction an F0 of 29.7 (9 x 3.3) would be required,

90 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

 4

Recombined Milk – Normal Concentration

• When recombining temperatures of 50°C to 70°C • The tolerated sterility failure rate attributed to
are used, care should be taken to limit the hold time thermophilic spores is 1:10,000 units (Anderson
to prevent the growth of thermophiles, as their et al., 2011).
optimum growth temperature is approximately 55°C • Cocoa powder in the formulation has been
(see Chapter 3, section 3.3.1, for more information). sufficiently hydrated so there are no dry cocoa
clumps or dry cocoa particles before the UHT
Assumptions used when deriving the required treatment step (if this assumption is not the case
F0 value in Table 4.2 are: a higher F0 value may be necessary).
• The product density is 1.07 g/mL; therefore, unit • The z value of thermophilic spores is 10°C
sizes of 125 mL, 250 mL and 1 L have weights of (which is coincidently the same as C. botulinum)
134 g, 268 g and 1,070 g, respectively. (Rigaux et al., 2013).
• The D value of thermophilic spores at 121.1°C is
3.3 min, derived from G. stearothermophilus (Rigaux
et al., 2013).

Table 4.2:
Theoretical recommended F0 value during UHT treatment of chocolate milk.

Unit size Number of thermophilic spores Theoretical required F0 value to

before UHT treatment (CFU/g) achieve failure rate of not more
than 1:10,000 units
125 mL 1,000 30
100 27
10 24
1 20
250 mL 1,000 31
100 28
10 25
1 21
1L 1,000 33
100 30
10 27
1 23

91
4.
Recombined Milk –
Normal Concentration

Formulation Homogenising effect of steam over-pressure

• Literature and studies report anecdotal Most steam injectors require a considerable over-
evidence of growth inhibition of Geobacillus in pressure of steam for their operation. It may be as much
dairy-based formulations. as 2 bar above the equilibrium pressure corresponding to
• Rather than primarily focusing on the required the required temperature of the milk. As a consequence,
spore log reduction, the acceptability criteria can the steam injected into the milk condenses very rapidly
be directed to the theoretical sterility failure rate of and the collapsing steam bubbles cause cavitation. This
packaged units, such as a failure rate of not more has a considerable homogenising effect.
than 1 in every 10,000 units (Anderson et al., 2011).
High steam temperature can affect taste
• Once the typical number of thermophilic spores in
An undesirable consequence of injected steam having a
a formulation before UHT treatment is determined,
high over-pressure is that the steam temperature is very
the theoretical required heat treatment (F0 value)
high. It can be as high as 155°C when there is a 2 bar
to achieve a sterility failure rate of no more than 1 in
over-pressure. The high steam temperature overheats
every 10,000 units manufactured can be determined
milk that is close to condensing steam bubbles. This can
as well (see Table 4.2).
cause chalky-textured sediment to form, which affects
UHT process the taste of the milk.

There are two basic modes of UHT process:

• Heating by direct contact with steam (direct
steam mode).
• Heating using heat exchangers (indirect mode).

UHT process by direct steam heating

The milk is first heated to about 75°C (or higher, up
to about 120°C in some plants) indirectly in heat
exchangers. It is then directly heated by steam, using
either an injection or infusion process.

Steam injection
In this process, heating is continued up to 140°C to 145°C
by direct steam injection (DSI) into the milk, with vacuum
flash-cooling after the holding section. The heating and
cooling times are very short – about 0.2 s for the rise
from 75°C to 140°C and the same time to cool again
(see Figure 4.1b). This results in a very low heat input into
the milk (integral temperature x time) and consequently
a low degree of ‘cooked’ flavour.

92 © FONTERRA CO-OPERATIVE GROUP LIMITED 2022

 4
EXPERT TIP:
In both types of direct-steam-
heating plant, volatile flavour
compounds may be lost in the

Recombined Milk – Normal Concentration

vacuum flash-cooling process.
This can be a problem when using
volatile flavour compounds in UHT
flavoured milks. Applying overage
to the flavour addition rate will
compensate for these losses.
Running a commercial trial will
validate the overage rate required.

Why the homogeniser is placed after the UHT section Steam infusion
Another undesired consequence of the high shear from In this process, the milk is sprayed into a steam chamber
steam injection is fat globule rupturing. Fat-casein with steam introduced at the pressure required to give
aggregates then form as the casein covers the newly the required final sterilising temperature. It needs only
exposed fat (Hostettler & Imhoff, 1963). For this reason, a small steam over-pressure so the resulting over-
DSI UHT plants place the homogeniser after the UHT temperature is negligible. Vacuum flash-cooling is carried
section to break down any heat-aggregated material out as it is in DSI plants.
that may cause sediment. In these plants, an aseptic
The effects on the product of steam infusion plants
homogeniser must be used because it is placed after
differ from those of steam injection plants in three ways:
the steriliser (UHT).
• There is no homogenising effect from the
In some types of plant, the steam over-pressure has
steam infusion.
been considerably reduced. The overheating effect on
the milk is then minimised by using a steam injector of • There is no local overheating of milk product in the
optimised design. However, the homogeniser must still infusion chamber.
be placed after the steriliser. • The residence-time distribution of the product at the
high temperature in the infusion chamber is broader
than in the holding tube of an injection plant, so the
total heating can be a little greater.

93
 EXPERT TIP:
Culinary quality steam must be used.
In either type of direct-steam-heating
process, the quality of the steam
is of the utmost importance. The
amount of steam condensed in the
milk during heating is considerable,
up to 10% of the volume of the milk
(for a 70°C temperature rise). Clearly,
culinary-quality steam must be used.
It must be free of boiler additives
and particulate matter. It should be
filtered before being fed to the UHT
plant, with stainless-steel piping from
the filter to the plant.

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4.
Recombined Milk –

Recombined Milk – Normal Concentration

Normal Concentration

UHT process by indirect heating In most indirect plants, as the homogeniser (two-
stage) is placed before the main heating step, it does
When heat exchangers are used for the entire heating not operate aseptically. However, aseptic (post-UHT)
and cooling range in UHT plants, the milk is heated homogenisation is required in some cases, because of
and cooled more slowly than in direct-steam-heating the types of product being processed (e.g. concentrated
plants. This means the total heat treatment is greater milk). Some types of indirect plant are fitted with tubular
(see Figure 4.1b). With no vacuum flash-cooling, there heat exchangers, with the process fed by a high-pressure
is no loss of volatile flavour compounds. Indirect plants pump. This pump also serves as the homogeniser
tend to foul more readily, so the running time between pump and the plant is constructed with the first-stage
cleaning and sterilising cycles may be shorter than for homogeniser valve (high-pressure drop) placed before
direct-steam-heating plants.

Figure 4.4:
UHT-sterilised recombined milk (standard process).

Direct steam heating Indirect heating

(From Figure 3.3) (From Figure 3.3)

↓ ↓
Recombined milk from WMP or SMP + fat Recombined milk from WMP or SMP + fat
↓ ↓
Pre-heat to 75°C–120°C indirect Pre-heat to homogenisation temperature 70°C–80°C
↓ ↓
Heat to 140°C direct steam
1
Homogenise 150–200 bar (total)
3

↓ ↓
Hold 4–6 s Heat to 138°C–140°C
↓ ↓
Vacuum flash-cool to original temperature (75°C–120°C) 2
Hold 3–4 s
↓ ↓
Cool to homogenisation temperature (approximately 75°C) Cool
↓ ↓
Homogenise two-stage 150–200 bar (total) (If homogenising post-UHT, cool to homogenisation
temperature 70–80°C and homogenise)3
↓
↓
Cool to filling temperature usually Cool to filling temperature usually
14°C–25°C (depending on product) 14°C–25°C (depending on product)
↓ ↓

Aseptic filling Aseptic filling

1. Some plants up to > 145°C. 3. Most indirect plants have only pre-UHT homogenisation (two stage);
2. Actually a little higher to balance injected steam. some have the first stage pre-UHT and the second stage post-UHT;
some have all stages post-UHT, as direct plants.

95
4.
Recombined Milk –
Normal Concentration

the UHT section. The low-pressure, second-stage of sterility failure. Therefore, it is very important that
homogeniser valve is placed after the UHT section, in the temperature sensors are accurately calibrated and the
aseptic part of the plant. temperature controller is working efficiently.

Ingredient selection
4.4.2
Fouling can be influenced by ingredient selection.
Characteristics of UHT-processed UHT plant fouling rates are considerably lower with
milk and defects reconstituted WMP (a half to a third) than with milk
recombined from SMP and fat. Including 5% to 10%
If the plant is well maintained and the process is well
(milk powder basis) of buttermilk powder (BMP) in
managed, so that sterility failure is not a problem,
the recombined milk will reduce fouling by 30 to 50%
production of fresh or recombined UHT milk is relatively
(Newstead et al., 1999).
trouble free.
Problems that may occur are excessive plant fouling or Milk acidity
shortened shelf life. Factors that limit the shelf life of The pH of the milk is a major factor in fouling. Calcium is
UHT-processed milk are: present in milk both as soluble ions in the serum and as
insoluble calcium phosphate bound up within the casein
• Gelation.
micelle. As the pH of the milk or beverage decreases,
• Sedimentation. calcium phosphate dissolves, releasing more calcium
• Heavy cream layer formation. ions. Conversely, an increase in pH shifts the balance
• Browning, when stored at high temperature (> 30°C). away from calcium ions to insoluble phosphates.
Decreasing the pH decreases the charge on the protein
UHT milk may last over a year, but in general reliable
as well. This reduces electrostatic repulsion between
shelf life estimates should be:
protein molecules, making interactions such as fouling
• From 3 to 6 months for direct- more likely. To limit fouling, the pH of UHT milk and milk
UHT-processed milk. beverages should be adjusted (where this is permitted)
• From 6 to 9 months for indirect- to between 6.7 and 6.9.
UHT-processed milk.
Water quality
The difference appears to be related to the extra heat
The quality of water used in recombining is important
treatment inherent in the indirect process.
also. Soft water, or preferably water purified by
This section addresses plant fouling and each of the shelf reverse osmosis, should be used. The presence of
life limiting factors above, as well as sterility failure. soluble minerals, especially calcium and magnesium,
has a significant effect on fouling rate. These minerals
Plant fouling initiate fouling by depositing on the surface of the heat
exchanger and by promoting aggregation of the protein.
Operating temperature
High levels of chloride, e.g. from seawater infiltration of
Fouling in UHT plants is very sensitive to operating coastal bores, can promote fouling as well. Processing
temperature. Raising the temperature by 1°C may water should meet the standards outlined in Table 4.3.
increase the fouling rate by 30% or more. Of course,
if the temperature is 1°C or 2°C too low, there is a risk

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EXPERT TIP:
Temperature and fouling
Raising the temperature by 1°C may
increase the fouling rate by 30% or

Recombined Milk – Normal Concentration

more. Of course, if the temperature
is 1°C or 2°C too low, there is a risk
of sterility failure. Therefore, it is
very important that temperature
sensors are accurately calibrated
and the temperature controller is
working efficiently.

Table 4.3: Figure 4.5:

Recommended maximum limits for water used Effects of pre-heat treatment applied to recombined
in recombining. milk on the subsequent fouling rate in the UHT plant.
The fouling rate is given as the rate of temperature
difference increase across the high-temperature heat
Odour and taste Not objectionable exchanger (heating-water-in minus milk-out).
pH 7.0 – 8.51
4
Total solids < 350 mg/L3
(temperature differential, °C/h)

Total hardness (as CaCO3) < 100 mg/L

3
Chloride (as Cl) 100 mg/L2
Fouling Rate

Nitrate (as NO3) 50 mg/L1 2

Iron (as Fe) 0.2 mg/L 1

Zinc (as Zn) 5.0 mg/L3 1

1. New Zealand Ministry of Health (2018).

2. FRDC research (Newstead et al., 1999). Limits given here are 0
stricter than those required by NZ or USA regulations and are A B C D E
based on fouling performance. Batch of SMP
3. Environmental Protection Agency (EPA), USA, 2020.

Control
Pre-heated 90°C 120 s

Milk powder heat class

Excessive heat treatment, during the manufacture of 2006; Srichantra et al., 2018). Therefore, it is strongly
either the milk powder or the recombined milk, increases recommended that these pre-heating sections be
UHT plant fouling (Newstead et al., 1999; Srichantra et removed or bypassed when processing recombined milk;
al., 2006; Srichantra et al., 2018). For this reason, milk otherwise shortened run times will result.
powder used for UHT recombined milk should be low to
low-medium heat class. In this respect, recombined milk Product recycle
seems to differ from fresh milk. Another cause of high fouling rates is a high proportion
of product recycle. In most plants, a small portion of
Pre-heat treatment the UHT-processed product is recycled back to the feed
There is a belief that a pre-heat treatment of fresh milk balance tank in order to match the production rate to
(typically 75 to 95°C for 30 to 120 s; Deeth & Lewis, the feed rate of the aseptic filler. Any recycled product
2017) before the UHT process reduces fouling in the has effectively been given an extra heat treatment (i.e.
high-temperature heat exchanger. Because of this belief, the previous UHT pass) before the final pass through
some UHT plant makers are now incorporating such a the UHT section. This has the same consequences as any
pre-heating section. other pre-heating step – the fouling rate is increased.
This problem can be minimised by ensuring that recycle
However, as stated above, this has the opposite
rates are kept below 5% (of the full product flow).
effect when recombined milk is being processed (see
Figure 4.5), (Newstead et al., 1999; Srichantra et al.,

97
4.
Recombined Milk –
Normal Concentration

Summary of steps to limit fouling: psychrotrophic bacteria) growing in the milk before UHT
processing. The UHT process kills the bacteria, but the
• Use low- or low-medium heat SMP, or a WMP with
enzymes may remain.
UHT specification.
• Be aware that increased whey content of the The cause is a milk hygiene failure, usually resulting
beverage may increase fouling. from holding the milk for too long with inadequate
refrigeration. Bacteria of this type do not produce
• If regulations permit, adjust the pH to between 6.7
significant levels of proteolytic enzymes until their
and 6.9, with phosphate, bicarbonate or citrate salt
numbers reach 107 (or more) CFU/mL (Fairbairn
or any combination of these.
& Law, 1986). See Chapter 3, section 3.3.1, for
• When fortifying with calcium or magnesium, use more information.
insoluble rather than soluble salts wherever possible.
The preventative control measure is to ensure that milk
• Follow the recommendations for process water (see
processing and storage are managed in such a way
Table 4.3 above and Chapter 2, section 2.2).
that bacterial numbers, as determined by the APC
• When making recombined milk, do not use (aerobic plate count) method, never exceed 106 CFU/mL
anhydrous milk fat (AMF) or vegetable oil without at any stage.
an appropriate emulsifier.
• Milk may be pasteurised before UHT, but extensive Cream layer formation
pre heat treatment of recombined milk before UHT A cream layer forms on the top of the milk through
(often referred to as ‘protein stabilisation’) is usually the natural flotation of fat globules to the surface.
unnecessary and should be avoided. The density of milk fat is about 0.92 g/mL (20°C) and
• Wherever possible, use aseptic tanks (A-tanks) the density of the fat-free aqueous phase of milk is
rather than recirculating UHT milk back through about 1.036 g/mL. The flotation of the fat is, therefore,
the UHT plant. inevitable. The rate depends on Stokes’ equation. Figure
• Avoid UHT temperatures above 145°C. 4.6 shows the distance fat globules of different sizes will
rise in 2 months in relation to a standard 1-litre tall-form
Gelation and sedimentation TetraBrikTM (as calculated using Stokes’ equation).

These appear to be related processes and a combination Fat rise is normally controlled by homogenisation, which
of both is often seen. Usually they occur naturally, reduces the fat-globule size and, therefore, their flotation
caused by complex interactions of the protein and rate. However, in UHT milk, the cream layer still forms
salt components of the milk. This process is slow, but because there is sufficient time for slow flotation during
variable, and is the basis of the shelf life limitations the long shelf life, as illustrated in Figure 4.6.
noted above (Table 4.1).
Stokes’ equation
Early gelation is usually caused by proteolytic enzymes For smooth rigid spheres, of radius, r, and density, ρf,
Similar processes may be caused by the action of low settling under gravity, g (= 9.8 N/kg), through a uniform
levels of proteolytic enzyme in the milk. Such a problem continuous phase of density, ρf, and viscosity, ηp, the
is usually the cause of early gelation, within a few weeks velocity, v, is given by:
and up to a few months after production. v = g(ρf – ρp) r2 2
9ηp
These enzymes are sufficiently heat resistant to survive
the UHT treatment. They come from bacteria (usually

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Recombined Milk – Normal Concentration

Protein membrane affects globule density Additive selection
The actual situation is not as simple as suggested above. The additives commonly used to control cream layer
The effective density of the fat globule, as it exists in formation are emulsifiers and hydrocolloid compounds,
milk, is greater than that of the fat itself. This is because such as carrageenans and vegetable gums. These may
of the protein-based membrane and the fact that be used separately, or together as compound blends.
protein is considerably denser than water. The mean
Compound blends are proprietary compounds
density of the globule is therefore dependent on the
collectively called emulsifier-stabilisers. They are most
amount of protein per surface area and on the
commonly blends of 90% mono- and diglyceride
surface-to-volume ratio (i.e. the size) of the globule.
emulsifier with 10% of a hydrocolloid gum blend, usually
containing κ-carrageenan.
A cream layer not always an issue
For UHT-processed milk, a cream layer inside the carton The emulsifier may reduce the average fat-globule
is not an issue if the cream layer stays liquid, does not size, but the effect is not large. This is because the milk
become cohesive and readily mixes back into the milk on proteins are such good emulsifiers in themselves that the
gentle agitation. emulsifier makes only a small (though often worthwhile)
difference. Refer to Chapter 3, section 3.2.2, regarding
In some cases, however, the cream layer becomes the use of emulsifiers.
cohesive or semi-solid through bonding interactions
within the cream layer once it has formed. When this
happens, the viscous cream layer may be observed
floating on the milk when it is poured out or may even Figure 4.6:
Schematic diagram illustrating the distance of upward
appear as lumps of semi-solid cream floating on the
flotation for fat globules of different sizes in UHT milk in
milk. When heated or poured into a hot drink, the lumps 2 months – scaled against a standard 1-litre TetraBrik™
may melt and break down into oily patches floating on for comparison.
the surface.

Globule Height of rise in

How to control cream layer formation
diameter 60 days (at 20°C)
Control measures include the selection of optimum
homogenisation conditions and the use of 0.6 µm 75 mm
selected additives.
0.7 µm 105 mm
Homogenisation conditions 1 litre
0.8 µm 140 mm
Homogenisation is more effective at higher temperatures;
70°C to 75°C is recommended (see Figure 3.14). 1.0 µm 190 mm 190 mm
Two-stage homogenisation is more effective than single-
stage homogenisation. The improvement is due to the
back-pressure from the second-stage valve increasing
the effectiveness of the action in the first-stage valve.
As a guide, the pressure applied to the second-stage
valve should be about 20% to 25% of the total pressure.
The total pressure should be in the range of 150 to 200
bar. Higher pressures, even up to 300 bar, create only a
very small improvement.

99
4.
Recombined Milk –
Normal Concentration

Purpose of hydrocolloid gums be dispersed in a post-UHT homogeniser and appear

The main purpose of the hydrocolloid gums is to increase only as a general darkening of the milk. Brown sediment
the viscosity of the milk. From Stokes’ equation, it can will usually form, which is readily identified using
be readily seen that doubling the milk viscosity (typically a microscope.
from 2.5 to 5.0 cP, which is barely noticeable to the The remedy is to avoid running the plant for too long
consumer) halves the rate of fat rise and therefore the between cleaning cycles. The need for cleaning can be
rate of cream layer formation. detected by watching for:
The milk made from WMP gives a more stable emulsion, • A high pressure drop across the high-temperature
less prone to cream layer formation, than the SMP-plus- heat exchanger.
fat system.
• A large increase in the temperature of the heating
medium – steam or hot water – entering the high-
Effects on fat-globule density
temperature heat exchanger; usually an increase of
These additives also affect the protein membrane 4°C to 5°C should be the limit.
around the fat globule and consequently the overall fat-
globule density. Mono- and diglycerides emulsifiers used Plant recycle rate
alone (at about 0.15% in recombined milk containing Yet another cause of browning and excessive ‘cooked’
3.5% fat) typically reduce the protein bound to the flavour is high plant recycle rates. As with fouling, the
fat globule from 8% to 4%. However, when the same problem can be minimised by keeping the recycle rate
emulsifier is combined with a hydrocolloid gum the down to 5% or less (see above under ‘plant fouling’).
fat-globule-bound protein may increase up to 12%,
depending on the hydrocolloid blend. Sterility failure
Milk browning The most common problem with fresh or recombined
UHT milk production is microbiological contamination.
Milk browning and its undesirable effects on flavour In by far the majority of cases, it is caused by incorrect
can be caused by incorrect storage temperatures, plant plant operation or maintenance.
cleaning cycle time, and plant recycle rates.
The UHT sterilisation and associated aseptic packaging
Storage temperature processes are extremely demanding and unforgiving of
neglect and errors. The only remedies are strict attention
At storage temperatures above 30°C, browning in
to maintenance and calibration, and generally good
the milk (usually accompanied by the development of
plant and process management procedures.
‘caramelised’ or stale flavour) cannot be avoided. At
temperatures below 30°C, browning is negligible. In fact, The most common failures are due to:
at 30°C, browning is hardly noticeable in < 6 months
• Inadequate aseptic filling machine maintenance.
and at 25°C, there is no noticeable colour difference
after 9 months. • Insufficient cleaning and sterilisation of the
plant post-UHT.
Plant cleaning cycle time • Filler, pipe-seal or gasket failure.
Browning and excessive 'cooked' or burnt flavours can • Aseptic valve steam seal failure.
also be caused by incorrect processing practices. When
a plant is run for too long without cleaning, deposit
builds up in the heat exchanger, turns brown and will
gradually flake off into the product. This material may

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EXPERT TIP:
Pay special attention to aseptic
homogenisers.
Aseptic homogenisers require special

Recombined Milk – Normal Concentration

attention as the wear of their seals is
high and they are difficult to clean. It
also takes a considerable amount of
heat to sterilise them because their
large metal mass acts as a heat sink.
Regular inspection is advised.

101
4.
Recombined Milk –
Normal Concentration

Highly heat-resistant spore (HHRS) defects Geobacillus spp.

These are thermophilic (heat loving) bacteria that
Bacillus sporothermodurans can grow in approximately 37 to 68/70°C (Burgess et
This mesophilic (moderate-temperature loving) al., 2010). They are commonly found in milk powder
bacterium produces spores resistant to UHT treatment manufacturing plants and are part of the natural
(highly heat-resistant spores or HHRS) (Scheldeman microflora of most dairy powder products.
et al., 2005).
The spores of most strains of Geobacillus are inactivated
B. sporothermodurans is not pathogenic. However, it at UHT temperatures. However, there are some strains
can cause minor spoilage defects, such as slight colour that produce HHRS, and will survive this treatment
changes, off-flavours and possible destabilisation of process (Hill & Smythe, 2012). These strains of
casein micelles (Klijn et al., 1997). It may also cause issues Geobacillus may be important spoilage bacteria for UHT
in relation to regulations because milk containing them products where powders are recombined because they
cannot be classed as ‘sterile’. can cause spoilage defects if products are held at abuse
temperatures of 37°C or higher (Hill & Smythe, 2012).
B. sporothermodurans is thought to have its origin
Refer to Chapter 3 for additional information.
in the natural environment (e.g. on farm or in feed)
(Scheldeman et al., 2005). However, this species is
selected for UHT manufacturing, particularly when
milk is recycled during processing or when returned
unsold product is reprocessed through UHT treatment.
Reprocessing returned product and laboratory test
samples is not recommended.

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Recombined Milk – Normal Concentration

4.4.3 The identity of the bacteria present will help to trace the
problem. For example, the presence of:
Microbiological control of
product – sterility targets and • Bacteria that are less heat-tolerant is an indication
of seal failure in the aseptic part of the plant or in
testing considerations the packaging itself.
Sterility failures are rare. If they were not rare, the • Bacteria known to survive UHT treatments raises
business would not be viable. The industry target for the possibility of contamination through some
aseptic product is less than one failure in 10,000 units. of the heated parts of the plant that were not
No practical sampling system is capable of trapping adequately sterilised, or were not properly cleaned
even a 1% failure rate. Therefore, the manufacturer and sterilised.
is dependent on scrupulous adherence to good
manufacturing practice and preventative maintenance 4.4.4
procedures to ensure product integrity.
Ingredient milk powder
Detecting major failures As noted above, milk powder used for UHT-processed
Routine in-factory testing is used to trap major failures recombined milk should not have a high heat treatment
(such as from a contaminated A-tank). This testing because this increases the tendency to cause fouling of
includes incubation of samples for 7 days at 30°C the plant (see section 4.4.2). Refer to Chapter 2 for more
followed by APC determination, or the use of the Charm information on ingredients.
EPIC™ assay, which measures adenosine triphosphate • SMP should be low- or low-medium heat.
(ATP) of bacterial cells present that are growing.
• WMP needs a defined minimum pre-heat treatment
Detecting minor failures to develop the antioxidant compounds required
to ensure flavour stability. However, because
The only way to detect low-level failure rates is through reconstituted WMP is less prone to cause fouling
customer complaints. Therefore, customer complaints than is SMP recombined with fat, the moderate
should be regarded as a useful tool rather than a heat treatment needed does not cause problems.
problem. They may give a chance for correcting plant
• Levels of bacterial spores should not be high;
faults before major problems develop.
below 1,000 thermophilic spores/g of powder
Testing failed or returned product is recommended (Hill & Smythe, 2012) (see
section 4.4.1).
Failed or returned product may be subjected to
microbiological testing. Colonies of resulting bacteria Comments on the selection and use of other ingredients,
can be easily identified using matrix-assisted laser flavourings, cocoa and emulsifier-stabiliser compounds
desorption/ionisation time-of-flight mass spectroscopy are included in section 4.4.2 and in Chapter 7, section 7.6.
(MALDI-ToF).

103
 EXPERT TIP:
Reduce the retort
temperature when using
a two-stage sterilisation.
This gives a significant
reduction in ‘cooked’
flavour and a lighter-
coloured product than
a single-stage sterilised
milk, while meeting the
required spore elimination.

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4.
Recombined Milk –

Recombined Milk – Normal Concentration

Normal Concentration

4.5
Retort-sterilised milk –
normal concentration
Distinguishing features of retort-sterilised
milk are given in Table 4.1 above.

4.5.1
Processing
The milk is recombined as described in Chapter 3 section
3.1 and must be homogenised at this stage, before filling
and sterilisation. Two basic sterilisation processes are in
common use.

Single-stage sterilisation
This is the simpler process. The recombined milk is filled
into bottles (glass or plastic) and hermetically sealed.
The bottled milk is then passed through the retort for a
sterilisation treatment of not less than 120°C for 10 min,
or the equivalent (e.g. 117°C for 13 min).

Two-stage sterilisation
In this process, the milk is first given a high-temperature
short-time heat treatment in continuous flow (usually a
little less than UHT conditions), filled into the bottles (not
aseptically) and sealed. The bottled milk is then sterilised
in the retort using a somewhat reduced heat treatment
Influences on flavour, colour and sediment formation
than used in the single-stage process.
The flavour and colour of two-stage sterilised milk are
The benefit of a two-stage process dominated by retort sterilisation effects. A reduction
The high-temperature continuous process stage is in the heat treatment applied in the retort (e.g. 116°C
designed to kill any heat-resistant spores in the milk. for 10 to 12 min), compared with a normal single-stage
Then, provided there is no reinfection with spores during retort process (120°C for 10 min), gives a significant
the bottle filling process, sterilisation in the bottles can reduction in these characteristics. But variations in the
be completed using a shorter heat treatment than is first stage of the process (130°C for 5 s compared with
necessary for the single-stage (retort-only) process. This 140°C for 5 s) have little effect.
shorter retort treatment creates a product with a less Higher heat treatment at either stage increases any
‘cooked’ flavour and a lighter colour than milk sterilised tendency to form sediment (as measured after 10 days
by the single-stage process. at 20°C).

105
4.
Recombined Milk –
Normal Concentration

Figure 4.7:
Retort-sterilised recombined milk.

Single-stage Two-stage

(From Figure 3.3) (From Figure 3.3)

Recombined milk from Recombined milk from

WMP or SMP + fat WMP or SMP + fat

Homogenise two-stage 75°C Homogenise two-stage

150–200 bar 75°C 150–200 bar

First-stage heat treatment

e.g. 130°C for 5 s

Cool to filling temperature Cool to filling temperature

(approximately 20°C) (approximately 20°C)

Fill and hermetically Fill and hermetically seal

seal bottles bottles (high hygiene)

Retort sterilise Retort sterilise

e.g. 120°C for 10 min e.g. 116°C for 10 min

Cool Cool

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 4
EXPERT TIP:
Use a rotary retort for both processes.
For single-stage and two-stage
processes, a rotary retort should be

Recombined Milk – Normal Concentration

used, i.e. a retort that rotates the
bottles as they are being sterilised.
This aids heat transfer into the bottles,
which enables the heating time required
to achieve effective sterilisation to be
minimised. This in turn minimises the
intensity of ‘cooked’ flavour developed
in the milk and reduces the likelihood of
sediment formation.

Comparing the single-stage and not be neglected because of an incorrect belief within the
two-stage processes industry that the second-stage, truncated sterilisation
process will prevent failures.
Figure 4.7 shows a schematic comparison of the
sterilisation of milk reconstituted from WMP or
recombined from SMP and fat by a single-stage retort 4.5.2
process and a two-stage process. Ingredient milk powder
Precautions For retort-sterilised recombined normal-concentration
The strategy of the two-stage sterilisation process is milk, low- and medium-heat SMPs are recommended.
sound only if there is no reinfection of the product by This is in contrast to sterilised concentrated milk
spores during the (non-aseptic) bottle-filling process. (evaporated milk – see Chapter 5, section 5.1), for
It is therefore essential that bacterial numbers in which expressly manufactured ‘heat-stable’ milk powder
the packaging are very low and a strictly hygienic is required.
environment is maintained around the filling operation. As with UHT-sterilised product, it is recommended
Bacterial levels in both the packaging and the that milk powder with thermophilic spore counts
environment should be monitored regularly. < 1,000 CFU/g be used, for the reasons discussed above
It is equally important that the integrity of the first- (section 4.4.1).
stage sterilisation is maintained at a high level. It must

107
References

1. Anderson, N. M., Larkin, J. W., Cole, M. B., Skinner, (2020). Retrieved from https://www.epa.gov/
G. E., Whiting, R. C., Gorris, L. G. M., Rodriguez, A., sdwa/secondary-drinkingwater-standards-
Buchanan, R., Stewart, C. M., Hanlin, J. H., Keener, L. guidance-nuisance-chemicals
& Hall P. A. (2011). Food safety objective approach
9. Fairbairn, D. J. & Law, B. A. (1986). Proteinases of
for controlling Clostridium botulinum growth and
psychotrophic bacteria: their production, properties,
toxin production in commercially sterile foods. Journal
effects and control. Journal of Dairy Research, 53,
of Food Protection, 74, 1956–1989.
139–177. doi.org/10.1017/S0022029900024742
doi.org/10.4315/0362-028X.JFP-11-082
10. Hill, B. M. & Smythe, B. W. (2012). Endospores of
2. Buehler, A. J., Martin, N. H., Boor, K. J. & Wiedmann,
thermophilic bacteria in ingredient milk powders and
M. (2018). Psychrotolerant spore-former growth
their significance to the manufacture of sterilized
characterization for the development of a dairy
milk products: an industrial perspective. Food Reviews
spoilage predictive model. Journal of Dairy Science,
International, 28(3), 299–312. doi.org/10.1080/87559
101(8), 6964–6981. doi.org/10.3168/jds.2018-14501
129.2011.635487
3. Burgess, S. A., Lindsay, D. & Flint, S. H. (2010).
11. Hostettler, V. & Imhoff, K. (1963). Studies on
Thermophilic bacilli and their importance in dairy
sedimentation and formation of a mealy-
processing. International Journal of Food
chalky texture of UHT steam-injected milk.
Microbiology, 144(2), 215–225. doi.org/10.1016/j.
Milchwissenschafft, 18(1), 2–6.
ijfoodmicro.2010.09.027
12. Kessler, H. G. (1981). Food Engineering and Dairy
4. Deeth, H. (2017). Optimum thermal processing for
Technology. Verlag A. Kessler, Freising, Germany.
extended-shelf-life (ESL) milk. Foods, 6(11), 102.
doi.org/10.3390/foods6110102 13. Klijn, N., Herman, L., Langeveld, L., Vaerewijck,
M., Wagendorp, A. A., Huemer, I. & Weerkamp,
5. Deeth, H. C. & Lewis, M. J. (2017). High Temperature
A. H. (1997). Genotypical and phenotypical
Processing of Milk and Milk Products. Wiley Blackwell,
characterization of Bacillus sporothermodurans
Chichester, United Kingdom
strains, surviving UHT sterilization. International
6. Diao, M. M., André, S. & Membré, J. M. (2014). Dairy Journal, 7(6–7), 421–428.
Meta-analysis of D values of proteolytic Clostridium doi.org/10.1016/S0958-6946(97)00029-0
botulinum and its surrogate strain Clostridium
14. Newstead, D. F. (1999). Sweet-cream buttermilk
sporogenes PA 3679. International Journal of
powders: key functional ingredients for recombined
Food Microbiology, 174, 23–30. doi.org/10.1016/j.
milk products. In Proceedings of 3rd International
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Symposium on Recombined Milk and Milk
7. Doll, E. V., Scherer, S. & Wenning, M. (2017). Spoilage Products. International Dairy Federation Special
of microfiltered and pasteurized extended-shelf- Issue No. 9902, 55–60. International Dairy
life milk is mainly induced by psychrotolerant Federation, Brussels, Belgium.
spore-forming bacteria that often originate from
15. Newstead, D. F., Groube, G. F., Smith, A. F. & Eiger,
recontamination. Frontiers in Microbiology, 8, 135.
R. N. (1999). Fouling of UHT plants by recombined
doi.org/10.3389/fmicb.2017.00135;
and fresh milk. Some effects of pre-heat treatment.
8. Environmental Protection Agency (EPA), USA. In D. I. Wilson & P. J. Fryer (Eds), Proceedings of a

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Conference Held at Jesus College, Cambridge,
6–8 April 1998; Fouling and cleaning in food
processing. 98, 17–24.
16. New Zealand Ministry of Health. (2018). Drinking
Water Standards for New Zealand 2005 (revised
2018). Wellington: Ministry of Health.
17. Renner, E. (1985). Konsummilch.
Molkereitechnik. Band 66/67. Verlag Th. Mann,
Gisenkirchen-Buer, Germany.
18. Rigaux, C., Denis, J. B., Albert, I. & Carlin, F. (2013).
A meta-analysis accounting for sources of variability
to estimate heat resistance reference parameters
of bacteria using hierarchical Bayesian modeling:
estimation of D at 121.1 °C and pH 7, zT and zpH
of Geobacillus stearothermophilus. International
Journal of Food Microbiology, 161, 112–120. doi.
org/10.1016/j.ijfoodmicro.2012.12.001
19. Scheldeman, P., Pil, A., Herman, L., De Vos, P. &
Heyndrickx, M. (2005). Incidence and diversity of
potentially highly heat-resistant spores isolated at
dairy farms. Applied and Environmental Microbiology,
71(3), 1480–1494. doi.org/10.1128/AEM.71.3.1480-
1494.2005
20. Srichantra, A., Newstead, D. F., McCarthy, O. J.
& Paterson, A. H. J. (2006). Effect of pre-heating
on fouling of a pilot-scale UHT sterilizing plant by
recombined, reconstituted and fresh whole milks.
Food and Bioproducts Processing, 84, 279–285.
doi.org/10.1205/fbp06027
21. Srichantra, A., Newstead, D. F., Paterson, A. H. J.
& McCarthy, O. J. (2018). Effect of homogenisation
and pre-heat treatment of fresh, recombined and
reconstituted whole milk on subsequent fouling of
UHT sterilisation plant. International Dairy Journal,
87, 16–25. doi.org/10.1016/j.idairyj.2018.07.009

109
5.
Recombined Milk
– Concentrated
This chapter provides an overview of
the background, formulation, processing
and ingredients used in
the making of:
• Recombined evaporated milk (REM).
• Recombined concentrated milk (RCM).
• Recombined sweetened condensed
milk (RSCM).
• Creamer – compared to sweetened
condensed milk.

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Ingredients
5
2

Recombined Milk – Concentrated

5.
Recombined Milk –
Concentrated

5.1
REM (unsweetened)

5.1.1
Background

Development
Approximate date for earliest record of sterilised evaporated milk
1796
• Its invention was attributed to Frenchman Nicolas Appert.
• Milk was concentrated to two-thirds original volume and sterilised in bottles
in a boiling-water bath.
• It was used to provision French warships in the early 1800s.
• Numerous developments followed.

First patent for unsweetened evaporated milk

1856
• Granted to Gail Borden in the USA.

USA patent for rotating steam steriliser

1884
• Granted to John Meyenberg, a Swiss immigrant.
• Overcame the main technical problem of milk tending to coagulate during
heat sterilisation.
• Rotating tin cans in a pressurised sterilisation vessel allowed for shorter
sterilisation times thereby reducing the tendency to coagulate.
• Enabled full commercial development of the product as we know it today.
• Led to practical concentration limits of 2 to 2.5 times the concentration of
normal milk for coagulation-free in-tin sterilisation.

Improved stability during heat sterilisation

1920s
• A pre-heat step, before the milk is concentrated, became recognised as important.
• This reduced coagulation of the concentrated milk during heat sterilisation.

Phosphate salts added to further improve heat stability

1940s
• Phosphate salts were used as stabilising additives (Hunziker, 1946).
• The basis for the present process, outlined in Figure 5.1, now existed.

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Recombined Milk – Concentrated

Characteristics
Table 5.1:
Use: The main uses of evaporated milk are as a tea and
Composition of evaporated milk standards.
coffee whitener, and a source of milk solids for bakery
and in preparing a range of food dishes, e.g. creamy
Fat Total solids Milk protein
soups and chowders, and desserts and pies. minimum minimum in milk
Flavour: Evaporated milk has a distinctive caramelised (% w/w) (% w/w) solids-
not-fat
flavour that is preferred by many consumers. minimum
(% w/w)
Viscosity: Consumers also prefer a particular texture
(viscosity) range, which varies from country to country. Codex 7.5 25 34
The viscosity is determined by the milk used (or for REM Alimentarius
the milk powder used), the level of stabiliser salts added,
American 8 26
permitted thickeners, and to some extent the particular
sterilisation conditions. British 9 31

Colour: The colour is pale brown, which is caused by the

Maillard reaction between amino acids and reducing
sugars, that also contributes to the flavour. Evaporated milk can be formulated to:
Shelf life: REM is shelf stable and designed to be • The American standard with 18% non-fat milk
stored at room temperature for long periods up to solids, so the 8% fat gives 26% total solids (TS).
12 to 24 months.
• The British standard with 22% non-fat milk solids,
Packaging: This product is typically stored in cans of so the 9% fat gives 31% TS.
varying sizes (e.g. 410 g or 150 g). Most cans require
The American standard is the most widely used because
a can opener; however, there a few, particularly
it is lower in solids and therefore cheaper to produce. It is
the smaller sizes (150 g), which have a ring pull for
also similar to the Codex Alimentarius standard.
convenience of opening.
There are other variations, such as low-fat versions, and
some regional manufacturers have their own particular
5.1.2 variants, e.g. 6% fat with 20% non-fat milk solids.
Formulation
Industry naming convention
The Codex Alimentarius standard for evaporated milks
(Codex, 2018a) is a widely recognised international In industry, these standard products are usually referred
standard. It defines the composition and includes raw to by their fat:non-fat milk solids contents, e.g. 8:18
materials, permitted ingredients and food additives. evaporated milk for the American standard and 9:22
There are also American and British historic standards. evaporated milk for the British standard.
Here is the composition for each. Basic formulations are given in Table 5.2, together with
recommended homogenisation conditions.

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5.
Recombined Milk –
Concentrated

Table 5.2:
Formulations for American and British standard REM – for a 1-tonne batch.
The figures are examples. Actual figures depend on a specific milk powder’s fat and moisture contents. The skim milk
powder (SMP) and whole milk powder (WMP) indicated are ‘heat stable’. BMP is the abbreviation for buttermilk powder.

Ingredients American standard (AS) British standard (BS)

From:
SMP (3.8% moisture, 0.8% fat) 186.0 kg 209.5 kg
BMP (9.0% fat, 3.8% moisture) (optional) 23.0 kg
Milk fat 78.5 kg 86.5 kg
Water 735.5 kg 681.0 kg
Phosphate stabiliser As required As required
From:
WMP (30% fat, 3% moisture) 268.0 kg 300.0 kg
Water 732.0 kg 700.0 kg
Phosphate stabiliser As required As required
Recommended homogenisation – 160 bar first stage, 160 bar first stage,
two-stage, 60°C–65°C 4 bar second stage 4 bar second stage

Note: American standard is 18% non-fat solids, 8% fat, 26% total solids.
British standard is 22% non-fat solids, 9% fat, 31% total solids.

The role of BMP When using WMP

In Table 5.2, no BMP is included in the formulations
When using SMP to make British standard REM based on WMP, for either of the two standards. WMP
It is very difficult to make SMP that has adequate heat can be manufactured to give a higher degree of heat
stability for making high-solids British standard (9:22) stability than can SMP. That is because the natural fat-
REM in which the SMP is the sole source of non-fat globule-membrane components still present in WMP are
milk solids. Adding BMP improves the heat stability separated out during the manufacture of SMP. In WMP,
of the recombined product. The BMP level is usually the effects of the fat-globule-membrane components on
equivalent to 10% of the total milk powder, as indicated heat stability appear to be greater than those obtained
in Table 5.2. Alternatively, lecithin is permitted under the by adding BMP as this natural membrane material is
Codex Alimentarius standard (Codex, 2018a). still associated with the fat globules (as illustrated in
Chapter 3, Figure 3.12). However, BMP is sometimes
When using SMP to make American standard REM included in WMP-based formulations with a resulting
It is relatively easy to make the lower solids American increase in heat stability.
standard (8:18) REM using heat-stable SMP without
adding BMP. However, BMP is often included because
it improves the heat stability (Newstead, 1999). These
effects are due to BMP containing natural fat-globule-
membrane components, including the phospholipid
(Chapter 3).

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 5
EXPERT TIP:
Use lecithin instead of BMP.
This is permitted under the Codex
Alimentarius standard. This can be
particularly relevant when using

Recombined Milk – Concentrated

SMP to make the high-solids British
standard REM.

Fat-filled REM
Fat-filled REM can be made from a blend of SMP and
vegetable fat (e.g. refined palm olein). The vegetable
fat replaces milk fat in the REM. This results in a lower-
cost product which has the flavour of the vegetable
oil present. Manufacturers require equipment to also
handle and dose the vegetable oil into the reconstituted
SMP, along with a homogeniser to ensure the vegetable
oil is well emulsified. The Codex Alimentarius standard
for a blend of evaporated skimmed milk and vegetable
fat (Codex, 2019b) specifies a minimum of 7.5% fat,
25% TS and 34% milk protein in milk solids-not-fat. An
emulsifier (e.g. soy lecithin) is added to the vegetable
oil to aid in emulsifying the fat and slow fat separation
during storage. BMP can be used to provide natural milk
fat globule membrane. An example formulation is shown
in Table 5.3.

Table 5.3:
Formulation for fat-filled REM – for a
1-tonne batch
(The figures are examples only. Actual figures depend
on the actual fat and moisture contents of the milk
powder. The SMP indicated is ‘heat stable’.)

Ingredient Codex standard*

SMP (3.8% moisture, 0.8% fat) 169.4 kg
BMP (9.0% fat, 3.8% moisture) 16.9 kg
Vegetable oil 77.3 kg
Emulsifier 2.0 kg
Water 735.5 kg
Carrageenan stabiliser (Optional)
Phosphate stabiliser As required

* 17.5% non-fat solids, 7.5% fat, 25.0% total solids.

115
 EXPERT TIP:
Use ‘heat-stable’ milk powder when
manufacturing a recombined REM.
As part of the grading procedure,
the powder is tested for heat
stability by making and processing
a pilot batch of REM.

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 5
5.
Recombined Milk –
Concentrated

Recombined Milk – Concentrated

5.1.3 1. Fill a number of cans with the evaporated milk.

Processing 2. Add different levels of stabiliser salt to each can

(see section 5.1.4).
Milk at 2 to 2.5 times its normal concentration will 3. Mark the cans and process them through the retort
normally coagulate during retort sterilisation. To avoid (with the previous batch).
this, important steps are included to increase the heat
4. Retrieve and inspect for any sign of coagulation.
stability of the concentrate. These steps include a
pre-heat treatment, which must be carried out before 5. Where there is no coagulation, measure the viscosity.
evaporation and homogenisation (Newstead et al. 1979), 6. Identify the stabiliser salt level that gave the
and selecting the correct level of stabiliser salt. required final viscosity.

Evaporated milk can be made from fresh milk or 7. Add this level to the whole batch, ready for canning
recombined milk and comparing the two processes and sterilisation.
can be useful. In the recombining-based process, some
From recombined milk
critical steps required when manufacturing directly from
fresh milk are already incorporated in the milk powder
Why you need a heat-stable milk powder
making process and do not need to be considered. This
following is a high-level summary of the two processes, When making REM the pre-heat treatment required to
which are also shown as a comparison in Figure 5.1. make the final product heat stable is applied to the raw
milk during the manufacture of the milk powder. The
From fresh milk REM will then be able to withstand sterilisation without
coagulating.
Starting from fresh milk, the essential steps are:
In the recombining plant, the heat-stable milk powder
1. Standardise the milk to the required fat:non-fat is simply recombined to the required final composition
milk solids ratio. (using any of the devices described in Chapter 3,
2. Pre-heat it, typically 110°C to 120°C for 30 s section 3.1.1) and processed in the same manner as the
(Newstead, 2006). concentrate prepared directly from fresh milk.
3. Evaporate to the required final concentration. The process, including the manufacture of the heat-
4. Homogenise. stable milk powder, is outlined in Figure 5.1. For
5. Determine the required level of stabiliser salts for comparison, it also shows the processing steps for
the batch (see below). making REM directly from fresh milk.

6. Add stabiliser salts to the whole batch. Can filling and sterilisation
7. Fill the cans and sterilise (typically 117°C for 13 min
or 120°C for 10 min). Leaving head-space when filling
When filling cans to be retort sterilised, it is important
Determining required level of stabiliser salts to leave adequate head-space to allow for the greater
The stabiliser salts are typically disodium phosphate thermal expansion of the liquid contents compared with
(Na2HPO4) and monosodium phosphate (NaH2PO4). the metal of the can. If the head-space is insufficient
Below is an overview of how the required level can the seams of the can will be strained, often without
be determined. visible sign. The cans then leak and, on cooling, may let
in contaminant organisms from the cooling water. The
head-space also allows for better mixing of contents

117
5. EXPERT TIP:
Try to avoid a prolonged heating step

Recombined Milk –
from 100°C to sterilisation temperature
and also avoid a prolonged cooling step

Concentrated
from the sterilisation temperature
down to 100°C.
Prolonged heating and cooling steps
increase the tendency for the product
to heat coagulate.

of the can and heat transfer in a rotary steriliser. For bacteria in evaporated milk are usually of the Bacillus
standard 454 g cans, 10% head-space is required. genus, and often include Geobacillus stearothermophilus,
B. licheniformis and B. coagulans (Kalogridou-
The role of sterilisation Vassiliadou, 1992).
Sterilisation is necessary to make a shelf-stable
evaporated milk by: How to sterilise cans of evaporated milk
Cans of evaporated milk should be rotated during
• Destroying pathogenic and
sterilisation. The consequent stirring of the contents
spoilage microorganisms.
ensures uniform heat treatment and facilitates more
• Inactivating microbial spores. rapid heat transfer. If the cans are not rotated, a layer
Microorganisms are readily destroyed by heating, but of coagulated milk solids may form round the inside of
spores require specific temperature–time combinations the can.
to inactivate them. Depending on the type of Typical sterilisation regimes are 117°C for 13 min or
microorganism present, spores not inactivated during 120°C for 10 min.
sterilisation can germinate during storage and result
in product food safety failure, or spoilage. Spoilage

Figure 5.1:
Making evaporated milk from fresh milk or heat-stable milk powder.

From fresh milk From recombined milk

Milk (standardised whole) Milk (whole or skim)
↓ ↓
Pre-heat (e.g. 110°C for 30 s) Pre-heat (e.g. 120°C for 120 s)
↓ ↓
Evaporate Evaporate and dry
↓
SMP/WMP
↓
Test heat stability in simulated evaporated
milk manufacturing process
↓
Heat-stable SMP/WMP
↓

Homogenise Recombine and homogenise

↓ ↓
Test optimum stabiliser level Test optimum stabiliser level
↓ ↓
Add stabiliser to batch and fill cans Add stabiliser to batch and fill cans
↓ ↓
Sterilise batch Sterilise batch

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 5
EXPERT TIP:
Adjusting pH in commercial
REM manufacturing.
During commercial REM manufacturing,
stabiliser salts can be added. The main

Recombined Milk – Concentrated

purpose of this is to shift the milk’s
pH towards the optimum value for
avoiding coagulation during sterilisation.
The salts used are monosodium
dihydrogen orthophosphate (MSP) –
NaH2PO4, which is acid with respect
to milk, and disodium monohydrogen
orthophosphate (DSP) – Na2HPO4,
which is alkaline. These salts are
permitted ingredients under the Codex
Alimentarius standard.

5.1.4 treatments during their manufacture. In the case where

the lesser pre-heat treatment (120°C for 30 s) powder
Effects of pH and stabiliser salts was used, the heat coagulation time remained below
that required for sterilisation (the 10 min dashed line),
Researching the effect of pH on coagulation even when the pH was adjusted to the optimum level.
during sterilisation When the higher pre-heat treatment (120°C for 120 s)
The basic commercial test for heat stability, as outlined powder was used, the heat coagulation time at the
in section 5.1.3 (determining required level of stabiliser natural pH was barely long enough to avoid coagulation
salts), essentially gives a pass or fail (coagulation) result. during the 10-minute sterilisation. However, even a small
For the purposes of research, a more useful measure is acid shift extended the heat coagulation time to provide
the heat coagulation time, which is the time taken for an adequate margin for successful sterilisation.
coagulation to occur at the sterilisation temperature.
The heat stability, as measured by the heat coagulation
time, is very sensitive to the evaporated milk’s pH Figure 5.2:
value (see Figure 5.2). Sometimes, the optimum pH Heat stability (heat coagulation time (min) at 120°C)
for maximum heat stability lies on the acid side of the versus pH of 26% total solids REM (8% fat, 18% non-fat
milk solids). Showing a comparison between two pre-
concentrate’s natural pH (see Figure 5.2) and sometimes
heat treatments used during the manufacture of the
on the alkaline side.
ingredient SMP. The natural pH of the evaporated milk
The effects of pH on heat stability are shown in is indicated. The pH shifts were made by adding
Figure 5.2 for two SMPs that had different pre-heat hydrogen chloride (HCl) (acid) and sodium hydroxide
(NaOH). (The dashed line indicates the time required for
retort sterilisation at 120°C). HCl, NaOH and potassium
hydroxide (KOH) (akali) are not permitted ingredients
under the Codex Alimntarius standard (Codex, 2018a).

30
Heat Stability -min. to Coagulate at 120°C

25

20
Natural pH

15

10

0
6.3 6.4 6.5 6.6 6.7
pH

Heat treatment: 120°C for 30 s 120°C for 120 s

119
5. EXPERT TIP:
Stabiliser salts can increase heat

Recombined Milk –
stability with minimal pH shift.
There is an additional benefit from

Concentrated
the added stabiliser salt itself, over
and above the simple effect of the pH
shift (see Figure 5.3). Adding a mixture
of the mono- and disodium salts
will often increase the heat stability
without moving the pH value due to the
broadening of the curve. This is because
the salts chelate soluble calcium,
which reduces calcium activity. Adjust
viscosity by selection of the appropriate
stabiliser (see section 5.1.3) and use of
permitted hydrocolloids.

Typical stabiliser salt concentration

Figure 5.3:
The concentration of phosphate salts is usually up to
Effects of the level of added phosphate on the viscosity
0.13% (10 mmol/L), seldom > 0.18% (14 mmol/L), in a
versus pH curve of sterilised (120°C for 13 min) REM,
26% TS evaporated milk (finished product basis). The salts
26% TS (8% fat, 18% non-fat milk solids).
are added to the concentrated milk as a 10% weight/
The salts were added to give increases in phosphate of weight (w/w) solution (up to 8 mL per 454 g (1 lb) can).
0.065 and 0.217 moles per kg and the pH was adjusted
by adding acid (HCl) and alkali (KOH). The viscosity was Other additives
measured after sterilisation. HCl, NaOH and KOH are
not permitted ingredients under the Codex Alimentarius Emulsifiers and hydrocolloid gums, or proprietary
standard (Codex, 2018a). combinations of the two (known as emulsifier-
stabilisers), may be used in REM. The hydrocolloid
gums are mainly added to increase the viscosity, to
70
meet consumers’ expectations. Lecithin (soy) is added
by some manufacturers to improve the heat stability
60 and ‘creaminess’. These effects are similar to those of
adding BMP.
50

5.1.5
Viscosity of REM (cP)

40 Ingredient milk powder

30
Certified heat-stable milk powder, SMP or WMP as
appropriate, is required for manufacturing REM. High-
heat heat-stable (HHHS) milk powders (SMP and WMP)
20
are specially manufactured to withstand the sterilisation
conditions in REM. Pre-heat treatment is critical in the
10 manufacture of heat-stable milk powder for REM. For
more information on ingredients refer to Chapter 2.
0
6.0 6.2 6.4 6.6 6.8 7.0 WPNI test: The whey protein nitrogen index (WPNI)
pH of REM prior to sterilisation test can be used to measure the extent of the pre-heat
treatment. However, the required pre-heat treatments
Control 0.065 mol 0.217 mol
phosphate/kg skim phosphate/kg SMS may be so extreme that the WPNI scale no longer shows
milk solids (SMS) a useful response, because virtually all of the whey
protein is already denatured (Newstead & Baucke, 1983).
Source: Augustine & Clarke (1990) For more information on WPNI, see Chapter 2.
Lab-scale testing: Powders are also tested for their
heat stability by making REM on a pilot or lab scale to
simulate manufacturing conditions. This method uses
visual observation for defects and testing viscosity of the
sterilised REM. Milk powders can be certified as heat-
stable using such a direct test (Newstead, 2006).

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 5
EXPERT TIP:
Adjusting viscosity in commercial
REM manufacturing
In industrial practice, the retort
sterilisation conditions are fixed and,

Recombined Milk – Concentrated

provided the concentrated milk does
not coagulate in the process, the
parameter of interest is the viscosity
of the sterilised product, as shown in
Figure 5.3.

Spore count: Heat-stable milk powder should not have during sterilisation without significantly affecting the
a high thermophilic (heat loving) spore count. flavour and viscosity during shelf life. Increasing this level
A restriction of 1,000 thermophilic spores/g or lower is of substitution above 10% to 20% further increases
recommended to minimise the risk of product spoilage the stability of REM to coagulation during sterilisation,
during its shelf life. however results in a product with less caramel flavour
and having a watery mouthfeel. Substituting SMP with
BMP: Normal good-quality BMP is satisfactory for use
MPC70 results in a slight decrease in milk solids in REM
in REM manufacture at levels up to 15% of the total
as MPC contains less lactose and minerals on a protein
powder. If higher proportions are used, the BMP should
basis. This decrease would need to be checked for
also be certified as heat stable.
compliance against the local standard’s minimum milk
Milk protein concentrate (MPC): MPC70 is a milk protein solids. Use of MPC as an ingredient in REM would require
concentrate containing 70% protein. Substituting a checking with the local regulations to see whether it
portion of the SMP with an MPC70 (up to 10% on a is permitted.
protein basis) makes REM more stable to coagulation

121
5.
Recombined Milk –
Concentrated

5.1.6 RCM differs from traditional evaporated milk and REM

in the following ways:
Problems
• It has a less caramelised flavour that is similar to a
Layering: A cream layer and a bottom sludgy layer slightly-cooked UHT milk.
naturally occur on standing. This does not cause
problems because there is always a head-space in • It is naturally white, lacking the characteristic pale
the can, so handling readily re-mixes the layers. The brown colour of evaporated milk.
formation of a semi-solid cream layer during storage • It has a shorter shelf life, similar to that of
is known but is rare. It may be related to the use of UHT-processed unconcentrated milk, which is
hydrocolloid gum additives. (3 to 9 months).
Small white specks: Referred to as lime-grain, these • Product is filled into cartons of various sizes
may form on the walls of the can and are usually visible (e.g. 250 mL, 500 mL, 1 L).
shortly after sterilisation. These appear to be nucleated
by calcium citrate, which is in excess of saturation in Despite these differences, RCM can be used where REM
evaporated milk. This defect is usually overcome by using has been traditionally used, such as in cooking, baking,
a higher level of phosphate stabiliser. tea and coffee.

Adapting the UHT process to produce

5.2 evaporated milk
Continuous-flow sterilised, Early attempts to produce evaporated milk using a

aseptically packed recombined

conventional UHT process for sterilisation, rather than
the traditional in-can retort-sterilisation process, met
concentrated milk (RCM) with difficulties. The product (at 26% TS) had a short
shelf life – gelation occurred, usually within 3 months.

5.2.1 Another common problem was heat-induced

aggregation (or coagulation) of the protein colloid
Background system. The technology used to control the heat stability
of conventional evaporated milk was found not to apply
What is RCM? to the UHT process.
RCM is similar to REM, but is sterilised in a continuous- These shelf life and stability problems were solved only
flow process and aseptically packed. by reducing the sterilisation temperature to under 130°C
It is sometimes referred to as UHT RCM (or UHT REM) and lengthening the holding time correspondingly.
because it is made using modified UHT manufacturing
plants. However, the sterilisation temperatures used 5.2.2
are below 135°C, which is the commonly accepted lower
Formulation
limit for a UHT process. The recommended sterilisation
regime for RCM is 125°C for 6 min holding. The range of gross compositions for RCM is similar to
that for REM, except that higher concentrations, such
as the British standard (9% fat and 22% non-fat solids),
are avoided.

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 5
EXPERT TIP 1: EXPERT TIP 2:
When making RCM with SMP, reduce High homogenisation pressures
the risk of sediment by including up to ensure aggregation dispersion.
0.1% orthophosphate salts. High homogenisation pressures are
A 1:1 (by weight) mixture of advised to ensure effective dispersion

Recombined Milk – Concentrated

monosodium dihydrogen and disodium of aggregation that may have
monohydrogen orthophosphates is formed in the sterilisation process.
recommended in the first instance. Two-stage aseptic homogenisation
However, if it is necessary to raise the pH with up to 200 bar first stage and 30
value slightly, disodium monohydrogen bar second stage (total 230 bar) at
orthophosphate can be used alone. 70°C – 80°C is recommended.

RCM is best made using WMP. SMP with fat can Sterilise
be used, but is more likely to give sediment in the The reconstituted concentrated milk is usually sterilised
finished product. through an indirect-heated UHT plant that has been
ĸ-carrageenan, up to 0.02%, can also be included also, modified by the addition of a six-minute holding tube
if an increased viscosity is required. after the high heat treatment.

In formulations based on SMP and fat, the addition Homogenise

of emulsifier (0.1% to 0.2% lecithin or a suitable
The homogeniser must run aseptically because it is
monoglyceride or mono- and diglycerides) is advised.
placed after the sterilisation section to disperse any
Emulsifier is not necessary when using WMP but may be
aggregated material that may have formed in the
preferred because of its effects on sensory characteristics.
sterilisation process.
Some manufacturers require a product with
characteristics similar to those of the traditional REM Cool before aseptic filling
and therefore add caramel flavouring and colour. The milk is then cooled before aseptic filling. If
carrageenan or other hydrocolloid gum is included in the
5.2.3 formulation, the milk should be cooled to below 14°C
for filling to ensure the gum–protein matrix forms a
Processing favourable microstructure.
This section contains a high-level summary of the main A diagrammatic summary of the process is shown in
steps for making RCM. Figure 5.4.

Reconstitute and add stabilising salts

WMP is reconstituted in water at 45°C to 50°C to
the required concentration and the phosphate salt Figure 5.4:
preparation is added as a 10% (w/w) solution. If no Summary of process for making RCM –
further additions are made, it is not necessary to continuous-flow sterilised.
homogenise before the sterilisation process.
Reconstitute WMP and additives
If SMP or further additives are used
↓
Homogenisation is necessary if the milk is prepared Homogenise 30–50 bar at 70°C–75°C
by recombining SMP and fat, or if hydrocolloid gum (not required for WMP without additives)
additives (e.g. carrageenan) or emulsifiers are included. ↓
In either case, a light homogenisation at 30 to 50 bar at Sterilise – continuous flow
(heat to 125°C, indirect, holding tube 6 min)
70°C to 75°C is adequate.
↓
If hydrocolloid gum is used, it can be dry-blended with the Cool to 70°C – 80°C and homogenise
milk powder and added through the powder-blending (two-stage 200/30 bar)
system (see Chapter 3, section 3.1.1). Emulsifiers can ↓
also be dry-blended with the milk powder, or they can be Cool (< 14°C) and pack aseptically
dispersed in hot water and added to the reconstituted
milk before homogenisation.

123
5.
Recombined Milk –
Concentrated

5.2.4 Characteristics
Ingredient milk powder Use: The main uses of sweetened condensed milk are
as a whitener/creamer for coffee and tea, a source of
RCM sterilised under continuous flow does not require milk solids in food preparation, and an ingredient in
a heat-stable milk powder, as is mandatory for retort- confectionery and bakery products.
sterilised evaporated milk, even though the nominal
heating regimes are similar (i.e. 125°C for 6 min for Flavour: Sweetened condensed milk tastes very sweet
continuous flow, compared with 120°C for 10 min for (from the high level of added sugar) and creamy, which
the retort process). Using high-heat or heat-stable makes it ideal for desserts, confectionery and providing
powders in the continuous-flow process tends to indulgence when added to tea or coffee.
produce sediment. Colour: Pale yellow.
The recommended powder types are the same as Viscosity: Very thick due to the high TS content.
those used for UHT recombined milk of normal milk
concentration. They are: Shelf life: Stores well at room temperature for long
periods, typically two years.
• SMP with a low- or low-medium-heat class.
Packaging: Traditionally packaged in cans (e.g. 397 g).
• WMP with a low-medium heat treatment.
Alternative packaging available e.g. plastic squeeze tube
Levels of bacterial spores should not be high. Below with a flip-top cap and flexible retort pouches.
1,000 thermophilic spores/g of powder is recommended.
Critical parameters
5.3 Sugar concentration: Sugar is used to preserve
sweetened condensed milk. The high sugar concentration
Recombined sweetened in sweetened condensed milk (typically 45% sugar and
condensed milk (RSCM) 27% water; water activity < 0.79) increases the osmotic
pressure to such a level that microorganisms are unable
to grow, with the exception of osmophilic yeasts and
5.3.1 moulds. RSCM is not heat-treated after packaging as its
Background high sugar content preserves it for a long shelf life. The
sugar concentration in the water phase must not be less
Manufacturing sweetened condensed milk uses an than 62.5% or more than 64.5%. At 64.5%, the sugar
old technology that came from the 19th-century solution reaches its saturation point and some sugar
developments mentioned in section 5.1.1. Although may crystallise, forming a sediment.
commercial production began early and was well
Breakdown of plant hygiene or processing procedures
developed by 1856, it is a complex process with critical
may result in the growth of osmophilic yeasts and
elements that must be closely controlled. Sweetened
moulds and subsequent spoilage. If the water activity
condensed milk is not a sterilised product. It is preserved
exceeds 0.85, then Staphylococci (including the
by its high sugar content.
pathogen Staphylococcus aureus) may be able to grow.
Consequently, strict plant hygiene must be maintained
so that these microorganisms do not contaminate
the product.

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 5

Recombined Milk – Concentrated

Table 5.4:
Comparison of American and British standard sweetened condensed milk.

Composition American standard (AS) British standard (BS)

(minimum %, w/w) (8% fat, 20% non-fat solids) (9% fat, 22% non-fat solids)
Fat 8.0 9.0
Non-fat milk solids 20.0 22.0
Sugar (sucrose)1 45.4 43.5
Total solids 73.4 74.5
Formulation from WMP (kg/tonne)
WMP (28% fat, 3% moisture) 289.0 319.5
Sugar (sucrose) 454.0 435.0
Seed lactose 0.5 0.5
Water 256.5 225.0
1
Based on a ‘sugar ratio’ (= 100 x sugar/(sugar + water), w/w) of 63%.

Lactose crystallisation: The lactose concentration in 5.3.2

sweetened condensed milk is above saturation, so
that crystallisation occurs. The crystallisation must
Formulation
be controlled to ensure the crystals are very small, RSCM formulation is controlled by local regulation. This
otherwise the product will have a ‘sandy’ texture. can be based on internationally recognised standards
Can filling: Unlike REM, there is no sterilisation step after such as the Codex Alimentarius standard, e.g. 8% fat
can filling. This means the filling must be carried out and 28% TS (Codex, 2018c). In addition, there are two
under highly hygienic conditions (near aseptic) to prevent basic compositions: the American standard (AS) and the
recontamination of the pasteurised product. In addition, British standard (BS). These are shown in Table 5.4. The
the head-space in the cans is minimised so there is no American standard is similar to the Codex Alimentarius
opportunity for mould growth. standard (2018c).

Viscosity: The viscosity must be controlled to meet As with other recombined milks, RSCM can be
consumer expectations. Possible ways to control formulated from milk fat and SMP, with or without some
it include pre-heat treatment of the milk (or milk BMP (typically 10%, powder basis), or from WMP, as
powder), homogenisation conditions and pasteurisation shown in Table 5.4. The American and British standard
conditions, and use of other dairy ingredients such compositions are typical, but there are other variations,
as MPC. such as low-fat products.
Common to all formulations is the limiting range of
‘sugar ratio’, i.e. sucrose:(sucrose + water), in the product.
This should be not less than 62.5% (w/w) (otherwise
bacterial growth will not be inhibited), and not more
than 64.5% or the sucrose may crystallise.

125
5.
Recombined Milk –
Concentrated

Adding seed lactose is necessary to control lactose In either case, a way to continuously reheat the mixture
crystallisation by nucleation of crystal formation, to after each main ingredient addition should be provided.
ensure that many small crystals (< 10 μm) are formed This is because the milk powder and the sugar, at
rather than fewer, larger crystals. To achieve this, the ambient temperature, will cool the mixture as they
seed-lactose powder must be very fine (see section are added. The required reheating is usually done by
5.3.4), because it is necessary to provide about one circulating the batch through a heat exchanger and back
million crystal nuclei per 1 mm3 (mL) of sweetened to the mixing tank.
condensed milk.
After mixing, the batch is pumped through a filter to
remove any small lumps of undispersed powder. The
5.3.3 recommended filter mesh size is 100 μm. However, the
Processing filter units should be larger than required for milk, so
the high viscosity of the RSCM does not cause a back-
There are several processes for manufacturing RSCM. pressure that is too high for the
Choosing a process may depend on the ingredients filter system.
selected. The formulation can be based entirely on dry
After filtration, the RSCM should be deaerated to
ingredients plus water, or liquid sugar can be used if
improve the homogeniser’s efficiency in the next stage.
that is a preferred source. If liquid sugar is used, an
It is best done by heating to 70°C–72°C and flash-
evaporation step is needed to provide the amount of
boiling into the deaerator vacuum chamber to give a
sugar required, without exceeding the amount of water
temperature drop of 5°C–7°C, to the homogenisation
required in the finished RSCM. It is also not feasible to
temperature, immediately before the homogeniser.
disperse and dissolve the milk powder in the liquid sugar.
Two WMP-based processes are outlined in Figure 5.5. If the (b) process in Figure 5.5 is used, based on liquid
One uses dry ingredients and the other uses liquid sugar sugar, with the evaporation step before homogenisation,
with evaporation. then the deaeration takes place in the evaporator and
no separate deaeration step is required. Deaeration will
Recombining also not be required when using a vacuum recombining
The milk powder is firstly reconstituted to a high system, such as illustrated in Figure 3.10 (see Chapter 3).
concentration (approximately 48% TS when using WMP,
Homogenisation
depending on the particular formulation). Secondly, the
sugar is then added. If the formulation is based on SMP Sweetened condensed milk requires only a light
and milk fat, it is usual to add the SMP first, then the homogenisation because the high viscosity of the
sugar and then the fat. product effectively retards separation (i.e. flotation)
of all but the largest fat globules. Homogenisation
After these main ingredients have been added, the
increases the viscosity and is the main and easiest means
concentration is usually about 72% TS (unless liquid
of viscosity control used during the overall process. The
sugar is being used), and the resulting viscosity is very
usual pressure range is 20 to 70 bar. Either single- or
high. A high-power mixing system is required to handle
two-stage homogenisation can be used (Choat, 1979).
the high-viscosity mixture.

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EXPERT TIP 1: EXPERT TIP 2:
Why the pressure range is Controlling viscosity with
limited to 70 bar pasteurisation temperature
The usual homogenisation It is seldom practical to increase the
pressure range has a top limit holding time, but small increases in
of 70 bar because significantly

Recombined Milk – Concentrated

pasteurisation temperature can give
higher pressures often result a useful increase in viscosity.
in excessively high viscosity and
age-thickening behaviour.

Pasteurisation
The pasteurisation step has two functions. The main pasteurisation conditions offers a possible way to
one is to eliminate any yeasts and moulds that may control the viscosity.
grow in the product. The second function is to develop
Following pasteurisation, the remaining process
the required viscosity. Pasteurisation conditions vary
must be carried out virtually aseptically to prevent
from manufacturer to manufacturer; typically in the
recontamination with yeasts or mould.
range 80°C to 90°C for 30 s to 3 min. Altering the

Figure 5.5:
Summary of the process for making RSCM with dry ingredients or liquid sugar.

(a) Dry ingredients plus water (b) Liquid sugar

WMP (28% fat) WMP (28% fat)
↓ ↓
Reconstitute water at 55°C Reconstitute water at 55°C
(48% TS at approximately 45°C) (45% TS at approximately 45°C)
↓ ↓
Heat to 55°C add sugar to Add liquid sugar to
approximately 72% TS approximately 53% TS
↓ ↓
Filter Filter
↓ ↓
Deaerate Evaporate to approximately
↓ 72% TS
↓
Homogenise approximately Homogenise approximately
65°C up to 50 bar1 65°C up to 50 bar1
↓ ↓
Pasteurise (80°C–85°C for 3 min)2 Pasteurise (80°C–85°C for 3 min)2
↓ ↓
Cool to 50°C Cool to 50°C
↓ ↓
Vacuum cool to 32°C3 Vacuum cool to 32°C3
↓ ↓
Add seed lactose and disperse Add seed lactose and disperse
↓ ↓
Hold to complete lactose Hold to complete lactose
crystallisation (approximately crystallisation (approximately
30°C, i.e. without active 30°C, i.e. without active
maintenance of temperature) maintenance of temperature)
↓ ↓
Fill cans4 (minimal Fill cans4 (minimal
head-space < 3.5 mL/can)5 head-space < 3.5 mL/can)5
↓ ↓
Avoid temperature fluctuations Avoid temperature fluctuations
through storage and distribution6 through storage and distribution6

1
Viscosity control point. 2 Typical only; viscosity control point – essentially aseptic from here on. 3 Bring solids to 73.4% by vacuum evaporation.
4
Sterilise cans, high-hygiene filling. 5 To inhibit mould growth. 6 To avoid uncontrolled growth of lactose crystals.

127
5. EXPERT TIP 1:
Become familiar with the

Recombined Milk –
relationship between heat treatment
and viscosity before embarking on

Concentrated
RSCM production.
There is a complex relationship
between the milk’s pre-heat
treatment (temperature and holding
time) and the resulting RSCM
viscosity. An effective way to visualise
this relationship is provided as a
response surface plot in Figure 5.6.

Lactose crystallisation clothing – including hats, face masks, overalls and

footwear – that is not worn anywhere else in the factory.
The condensed milk leaves the cooling section of the
pasteuriser at about 50°C and is further cooled, to 30°C Finally, to limit the growth of any stray mould
to 32°C ready for seed-lactose addition. Usually this contaminants that may get into the product, the cans
cooling step is carried out by vacuum evaporating the are filled with minimal head-space. The accepted limit is
batch to the final required TS concentration. During this < 3.5 mL of air per standard 397 g (300 mL) can.
process 10% of the water may be removed.
Seed-lactose powder is added at a rate of about 500 g 5.3.4
per tonne (0.05%) of sweetened condensed milk. It Ingredients
must be α-hydrate, very finely ground, free flowing and
sterile or nearly so (otherwise it will recontaminate the Milk powder
pasteurised product). It must be rapidly and thoroughly
dispersed through the batch by vigorous agitation – this Milk heat treatment, or milk powder selection, is one
process may be assisted by continued vacuum boiling. way to control the viscosity of sweetened condensed
The objective is to nucleate the formation of about milk. However, sometimes too much emphasis is put on
1 million crystals per 1 mm3 (mL). If this is achieved, the specifying the pre-heat treatment range in an attempt
crystals will be in the required size range (Jones, 1979a). to control the viscosity, without understanding the
nature of the response.
The seed lactose can be added either directly as a
powder or as a slurry dispersed in sweetened condensed In general, low pre-heat treatments will give low
milk. The slurry method is recommended as it is simpler viscosity, but high-heat treatments do not necessarily
to control. Whichever method is used, the addition give proportionately high viscosities.
must be near aseptic, i.e. there must be no possibility of
What the surface plot in Figure 5.6 reveals
contamination by osmophilic (high sugar concentration
loving) yeast or mould organisms. Although a simple increase in temperature or holding
time in some areas of the surface will produce an
After the seed lactose has been added and dispersed increase in viscosity, it is simplistic to treat this as a
and the batch brought to the final desired TS general rule. For the longer pre-heat holding times,
concentration, it is transferred, without further cooling, the viscosity passes over a maximum and falls again.
to the crystallisation tanks. Crystallisation is continued Increasing the heat treatment beyond that point
with constant agitation for several hours. decreases, rather than increases, the viscosity. In other
areas the surface is quite flat, so even moderate shifts in
Filling
heat treatment produce very little change in viscosity.
The filling process must be carried out under near-
aseptic conditions. The can filler should be in a separate Sugar (sucrose)
room that is free of potential spoilage organisms, Sugar quality is very important because more than 40%
particularly yeasts and moulds, and air conditioned with of sweetened condensed milk is sugar. If crystalline sugar
filtered air. The cans and lids should be hot-air or flame is used directly, without further purification, it should be
sterilised immediately before filling. A1 refined grade (for a detailed specification, refer to
The filling room is a critical hygiene area. Operator Jones, 1979b). The essential minimal requirements are:
activity in the filling room should be kept to a minimum. not less than 99.9% sucrose, no discolouration, moulds
Operators entering the area should wear hygienic < 10/10 g and yeasts < 10/10 g. If liquid sugar is used, it

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EXPERT TIP 2: EXPERT TIP 3:
Medium-heat powders Whey protein nitrogen index
are usually selected. (WPNI) limitations
Extreme pre-heat treatments are The WPNI scale is not always useful
generally avoided. To achieve the when manufacturing RSCM. For

Recombined Milk – Concentrated

right viscosity when using SMP, the example, the response surface in
medium-heat classification is usually Figure 5.6 shows that as the pre-heat
selected. WMP is normally made using temperature is increased, for a given
a medium-heat process, so standard holding time, the product viscosity
WMP of the required fat content is passes over a maximum and falls again,
usually suitable for RSCM. whereas the WPNI continues to decrease
with increasing pre-heat temperature.

Figure 5.6:
Response surface – viscosity of
RSCM after 28 days at 30°C 45
versus pre-heat treatment
(temperature and holding time) of
Viscosity (Poise)

35
milk during SMP manufacture.

Data is averaged from multiple

milk samples, each pre-heated 25
at 85, 95, 105, 115 and 125°C
for holding times at each
15
temperature of 2, 10, 60 and 240
s before manufacture of SMP 240
and preparation of RSCM. The
RSCM was prepared without 60
homogenisation. (Source: Fonterra 125
10 115
Research and Development Centre
105
experimental data.) 2 85 95

Pre-heat Hold Time (s) Pre-heat Temperature (°C)

may need further refining. Guidelines for this are given by In reality, satisfactory seed lactose consists of a few
Choat (1979). relatively large particles and a very large number of very
small particles, probably 0.1 μm3 or less (Jones, 1979b).
Seed lactose Satisfactory lactose powder can be obtained by grinding
As stated in sections 5.3.2 and 5.3.3, effective control to the point where > 99.9% (w/w) are < 45 μm long, the
of lactose crystallisation is critical to producing good- largest particles being relatively very few in number.
quality sweetened condensed milk. The seed lactose is
crucial to this process. Essentially, seed lactose is very
Sterilisation
finely ground α-hydrate (C12H24O12.H2O). It must be low To obtain satisfactory sterilised (or near-sterilised)
in moisture, free flowing with no tendency to cake or seed-lactose dust (i.e. very fine powder), the following
lump, and of low microbiological count, i.e. moulds procedure may be followed (Hunziker, 1946).
< 10/10 g and yeasts < 10/10 g.
1. Heat commercial α-lactose hydrate powder
Fineness to 93°C, preferably under vacuum, to
convert it to the α-anhydride form.
For practical purposes, the specification requires that the
2. Grind the α-anhydride using an impact
seed-lactose powder fineness is such that not more than
pulveriser mill.
500 g of seed lactose per tonne of RSCM will develop not
less than 1 million lactose crystals per cubic millimetre of 3. Fill the resulting lactose dust into cans,
finished product. This requires an average seed particles seal them and sterilise in an oven at
volume of about 0.4 μm3. approximately 130°C for 1 to 2 h.

129
5.
Recombined Milk –
Concentrated

MPC Other additives

RSCM products increase in viscosity over time. Replacing The only additive permitted by Codex Alimentarius
the SMP ingredient with an MPC, such as MPC70, is a (Codex, 2018c) for sweetened condensed milk is calcium
way to mitigate this increase. Up to 25% of the protein in chloride, as an aid to increasing viscosity. Addition rates
RSCM can be replaced with MPC70 without appreciably should be < 0.5 g/kg.
changing the properties of the final product (see Figure
5.7). Replacing 50% of the protein with MPC70 results
in a more consistent viscosity with very little change
5.3.5
over shelf life; typically, RSCM increases in viscosity over Problems
time (see Figure 5.7). Partially replacing SMP with MPC
Below is a quick guide to troubleshooting some
will lower the viscosity compared to formulations with
of the common problems that occur during
SMP only. However, by increasing the homogenisation
RSCM manufacturing.
pressure the target viscosity can be adjusted to meet
the consumer preference. Local regulations would need Mould ‘buttons’ in the can: Usually caused by product
to be checked to see whether MPC can be used in RSCM contamination and excessive head-space. Check and
and if the reformulated product meets with the milk correct the integrity of the process hygiene, particularly
solids standard. in the filling area. The filling operation should be
corrected to also, reduce the head-space.
Gas production causing bulged cans: Caused by
Figure 5.7: osmophilic (high sugar concentration loving) yeast.
Effect of substituting SMP with MPC70 (protein basis) Improved process hygiene is required.
on the viscosity of RSCM stored at 30°C for 6 months.
Control is no MPC70 substitution. Objectionable smell and flavour (rancid, cheesy): Usually
caused by osmophilic bacteria. Check the product for
3000
these organisms and thoroughly clean and sanitise the
entire plant, including sugar storage etc., as this may be
2500 a bacterium that can survive the whole process. It must
be eliminated from the plant.
Viscosity RSCM (cP)

2000 Sandy texture: Caused by large lactose crystals. Confirm

this using a microscope. Check the suitability
1500 of the seed lactose. Improve the lactose crystal
seeding operation.
1000 Wrong viscosity: Often caused by variation in the
ingredient milk powder. Adjust the homogenisation
500 conditions, and the pasteurisation temperature (if there
is latitude) or, as a last resort if the viscosity is low, add
calcium chloride.
0
0 1 2 4 6
Months of Storage at 30°C

Control 75% SMP + 50% SMP +

25% MPC70 50% MPC70

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EXPERT TIP:
Achieving consistent viscosity
It is recommended that the milk
powder is purchased from a reliable
supplier that will deliver a consistent

Recombined Milk – Concentrated

product, and that the viscosity of
the RSCM is fine-tuned by adjusting
the homogenisation conditions.

5.4 Lactose crystallisation: Partial replacement of SMP with

whey powder does not decrease the lactose content and
Creamer may increase it, depending on how much whey powder is
included. Therefore, it is still necessary to control lactose
crystallisation, as it is with sweetened condensed milk.
5.4.1
A hypothetical formulation: A typical (but hypothetical)
Background formulation is shown, compared with American standard
Creamer is an RSCM substitute for use in coffee and tea. RSCM, in Table 5.5. The formulation used is hypothetical
Although it is not strictly a concentrated milk, because it only and is not based on any actual commercial product.
does not conform to the Codex Alimentarius standards No emulsifier is included in this formulation. It should not
(Codex, 2018a, b, c), it is included here because of its wide be necessary in this case, provided the right type of whey
market acceptance. powder is used.

5.4.2 5.4.3
Formulation – compared to sweetened Processing
condensed milk Following formulation and recombining, processing
should in all respects be similar to that outlined for
This type of product is technologically similar to sweetened
RSCM in section 5.3.
condensed milk, but it has a different composition.
Formulations vary, and most are trade secrets. However,
all are based on the following formulation principles
(compared to sweetened condensed milk).
Table 5.5:
Milk solids: The skim milk solids content is reduced, the Comparison of a typical creamer with American
milk fat is replaced by vegetable fat and the fat content standard RSCM.
is increased. This maintains about the same whitening
effectiveness. A portion of the skim milk solids content is Composition Creamer American
replaced, often with whey powder or some other lower- (minimum %, w/w) (typical, standard (AS)
notional) (8% fat, 20%
cost ingredient.
non-fat solids)
Emulsifier: With a raised fat content and reduced protein Milk fat 8.0
content, there may be a deficiency in protein available to Vegetable fat 10.0
emulsify the fat effectively, so an emulsifier compound Skim milk solids 15.0 20.0
may be added. Whey powder 3.0
Carrageenan 0.02
Viscosity: With the reduced protein content, additional
Sugar (sucrose)1 45.4 45.4
measures may be taken to obtain the required viscosity.
Total solids 73.6 73.4
These measures include selecting whey powder with 1
Based on a sugar ratio of 63%
an appropriate mineral composition and the use of (100 x sugar/(sugar + water), w/w).
hydrocolloids, such as carrageenans.

131
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 5
References

Recombined Milk – Concentrated

1. Augustine, M-A. & Clarke, P. T. (1990). Effects of 11. Newstead, D. F. & Baucke, A. G. (1983). Heat stability
added salts on the heat stability of recombined of recombined evaporated milk and reconstituted
concentrated milk. Journal of Dairy Research, 57, concentrated skim milk: effects of temperature and
213–226. doi.org/10.1017/S0022029900026820 time of pre-heating. NZ Journal Dairy Science and
Technology, 18, 1–11.
2. Choat, T. (1979). Recombined sweetened condensed
milk and recombined filled sweetened condensed 12. Newstead, D. F., Conaghan, E. F. & Baldwin, A. J.
milk. In Recombining of Milk and Milk Products. IDF (1979). Studies on the induction of heat stability
Bulletin Doc. 116, Chapter 3, p. 23. International in evaporated milk by pre-heating: effects of
Dairy Federation, Brussels, Belgium. milk concentration, homogenisation and whey
proteins. Journal of Dairy Research, 46, 387–391.
3. Codex (2018a). Codex Standard for Evaporated Milks.
doi.org/10.1017/S0022029900017374
CODEX STAN 281–1971. Codex Alimentarius, FAO/
WHO, Rome, Italy. 13. Newstead, D. F. (1999). Sweet-cream buttermilk
powders: key functional ingredients for recombined
4. Codex (2018b). Codex Standard for a blend of
milk products. In Proceedings of 3rd International
Evaporated Skimmed Milk and Vegetable Fat. CODEX
Symposium on Recombined Milk and Milk Products.
STAN 250-2006. Codex Alimentarius, FAO/WHO,
International Dairy Federation Special Issue No.
Rome, Italy.
9902, pp. 55–60. International Dairy Federation,
5. Codex (2018c). Codex Standard for Sweetened Brussels, Belgium.
Condensed Milks. CODEX STAN 282-1971. Codex
Alimentarius, FAO/WHO, Rome, Italy.
6. Hunziker, O. F. (1946). Condensed Milk and Milk
Powder. 6th edn Hunziker, LaGrange, IL, USA.
7. Jones, R. E. (1979a). Seed lactose. In Recombining
of Milk and Milk Products. IDF Bulletin Doc. 116,
Chapter 11, p. 49. International Dairy Federation,
Brussels, Belgium.
8. Jones, R. E. (1979b). Sucrose. In Recombining of Milk
and Milk Products. IDF Bulletin Doc. 116, Chapter 9,
p. 44. International Dairy Federation, Brussels, Belgium.
9. Kalogridou-Vassiliadou, D. (1992). Biochemical
activities of Bacillus species isolated from flat
sour evaporated milk. Journal of Dairy Science,
75(10), 2681–2686. doi.org/10.3168/jds.S0022-
0302(92)78030-8
10. Newstead, D. F. (2006). Heat Grades of Milk Powder
for Recombined Products – fact and myth. In 5th
IDF Conference on Recombination, Fortification and
Supplementation. 27th IDF World Dairy Congress,
Shanghai, China, 23 October 2006.

133
6.
Creams
This chapter outlines the basic principles
of recombined creams and how to make
them. It covers the main ingredients used,
the various applications of recombined
creams and the processing involved in
their manufacture.

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6

Cream
6.
Creams

6.1
Introduction
When fresh cream is not an option due to Recombined creams are blends of dairy fat, dairy
cost or local supply, recombined creams are a powders and non-dairy ingredients. They can be
great alternative in a variety of applications. formulated ranging from 5% to 40% fat. The fat
content strongly influences the cream’s functionality,
Recombined creams can be used ‘fresh’ in products such and is chosen to suit the cream’s intended application.
as ice-cream and soups, or heat-treated by pasteurising Countries have restrictions on what is considered a
or ultra-high temperature (UHT) processing into a shelf- ‘cream’, so please refer to the regulatory requirements
life-stable product. of the intended sales markets.

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EXPERT TIP:
Care with protein concentrate levels.
Depending on the functionality of
the final cream, protein concentrates
used at high levels can negatively
impact some applications, such as

Cream
whipping, ice cream and cooking.

6.2
Ingredients
The dairy ingredients used in making
recombined creams are critical to
achieving a desired flavour and
functionality. See Chapter 2 for more
information on dairy ingredients.

6.2.1
Fat source
Anhydrous milk fat (AMF) is the main fat contributor for
recombined creams. Depending on the final application,
the recommended addition rate is up to 40%. AMF will
provide flavour and colour to the final product.
Alternative fat sources are frozen cream and
cream powder.
Non-dairy oils, such as vegetable fats, can be used to
manufacture creams, however, factors such as flavour,
functionality and mouthfeel can be impacted.

6.2.2
Dairy powders
Dairy powders provide flavour and some functionality
to recombined creams. They contain lactose, protein
and low levels of fat that will enhance the cream’s
flavour. Fonterra has a large range of powders to suit
preferred flavour profiles and functionality. Whole milk
powder (WMP), skim milk powder (SMP) and buttermilk
powder (BMP) are great additives for flavour. Whey
protein concentrate (WPC) and milk protein concentrate
(MPC) can be used to increase the protein content.

137
 EXPERT TIP:
Optimising the emulsifier
addition rate
The main emulsifier used in
cream is mono- and diglycerides
of fatty acids. These can be used
at an addition rate of 0.05% to
0.4%. Adding too much or too
little emulsifier can harm shelf
life stability and functionality.
A trial with lower and higher
emulsifier levels is recommended
to optimise the addition rate.

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6. EXPERT TIP:
Selecting the right stabiliser or blend

Creams
Stabilisers can be used in isolation
or as a blend to provide the intended
functionality to the cream. Stabiliser
suppliers can provide pre-made blends

Cream
to suit your intended application,
or give recommendations on which
ingredients to use.

6.2.3 Flavours
Non-dairy ingredients Flavours can be added to the recombined cream to
enhance or create flavour characteristics that are
Non-dairy ingredients play an important desirable in the final product. Liquid and powder flavours
role in a recombined cream’s functionality can be used. Pre-hydrating powder flavours, before they
are added into the cream, is recommended. Flavours
and shelf life stability.
should be added as the last ingredient prior to any
Emulsifier further heat treatment, such as UHT or pasteurisation.

Fresh creams have a layer surrounding each fat globule

that helps emulsify dairy fat. In a recombined cream
this layer is not present, so emulsifiers must be added to
reduce the fat’s surface tension and prevent fat globules
from coalescing (process by which two or more fat
globules fuse to form a bigger fat globule). Coalescence
will lead to instability in the pack, which is seen as a
cream plug or thick top layer. The emulsifier addition
rate depends on the percentage of fat in the cream
and the homogenisation pressure. These two factors
influence the fat surface area that needs to be coated
and therefore the amount of emulsifier required.

Stabilisers
Stabilisers have the ability to hydrate to form a network
that binds water. This increases the viscosity of the
continuous phase and acts to support the cream. The
increase in viscosity decreases the chance of flocculation
(small particles in suspension that aggregate, forming
large clusters or flocs) or coalescence over shelf life.
Stabilisers can help provide functionality to the cream to
suit its intended final application.
For recombined creams that are used ‘fresh’ in other
applications, the non-dairy ingredients will vary greatly
based on these formulations and in some cases may
not be required. For recombined creams with long
shelf lives, it is best to use a combination of emulsifiers
and stabilisers to achieve the intended shelf life. Shelf
life is dependent on cream performance and will need to
be assessed on an individual formulation basis; typically
4 to 9 months can be achieved. See section 6.3 for more
specific information based on final applications.

139
6.
Creams

6.3 6.3.1
Applications Whipping
For whipped creams to form a stable fat-globular matrix
Recombined creams are mainly used for the fat content should be 35% to 40% as for natural
whipped cream, as a cooking ingredient, cream. For a lower fat content cream, alternative
and to make confectionery or dairy products. ingredients will be required to support the foam
Each application benefits from a cream with structure. These will mainly be stabilisers that provide
unique attributes, developed through precise the foam with a higher viscosity to prevent syneresis
formulation and processing. (liquid separation from a gel).
Depending on the shelf life of the recombined cream,
whipping creams are typically UHT sterilised and
aseptically packed. Alternatively, recombined creams
can be pasteurised with a shorter shelf life. Retort
sterilisation is not advised for whipping cream.
Table 6.1 shows an example formulation for a 40%
fat whipping cream. MPC can be used to increase the
protein content.

Table 6.1:
Example 40% fat whipping cream formulation.

Ingredients %
Fonterra Anhydrous Milkfat 40.0
Fonterra Skimmilk powder 6.7
Polysorbate 60 (Emulsifier) 0.3
Glyceryl monostearate (Emulsifier) 0.1
Stabiliser 0.2
Salt 0.2
Preservative 0.1
Water 52.4
100.0

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EXPERT TIP:
Why the right stability is important
Cream stability over shelf life is a
primary problem for UHT creams
made with recombined creams. Fat
separation can easily occur if the

Cream
cream is not homogenised effectively.
However, if the product is too stable
there will be an issue with the cream’s
whipability. This is because the fat
globules must be destabilised to form
the foam and hold it for an intended
amount of time.

Typical manufacturing method 6.3.3

1. Heat the water to 60°C (140°F) in a tank Confectionery
under agitation.
Recombined creams can be used as a base ingredient
2. Dissolve the SMP, premixed with the
for a range of confectionery or dairy food products.
stabiliser and the preservative, in the water
using constant agitation. For example:
3. Hydrate for 5 to 10 min. • Ice cream.
4. Add the melted fat and emulsifiers. • Frozen dairy desserts.
5. Mix in a high-shear mixer to disperse the fat. • Yoghurt.
6. Heat to 70°C (158°F). • Soup manufacturing.
7. Pasteurise at 70°C (158°F) for 10 min, or
Using recombined creams for these products is much
at 85°C (185ºF) for 15 s.
more prevalent in markets where fresh alternatives are
8. Homogenise at 50 bar in two steps (35/15 bar). not available.
9. Cool to 20°C (68°F).
The fat content of these base recombined creams is
10. Add salt. typically 38% to 42%, as it is in fresh cream separated
11. Pack into a container and refrigerate. from raw milk. The creams are used as a fat source for
standardising the final product to its formulation. The
6.3.2 main packing format is bulk pack, typically pasteurised.
Alternative options are UHT or frozen.
Cooking
The key attribute required for a recombined cream used
Recombined creams intended for chef use in cooked in confectionery products is its ability to be easily mixed.
applications, such as pasta and soups, can be used
straight after recombining, pasteurised for short
shelf life or UHT-processed for an extended shelf life.
A cooking cream’s main desirable attributes are heat
and acid stability. This ensures there is no separation or
curdling when added to pasta and soups.
These creams are typically 15% to 35% fat content,
based on functionality requirements. Stabilisers
and thickening agents, such as starch, can help give
recombined cooking cream the required functionality.

141
6.
Creams

6.4 • Processing technologies needed – size and number

of tanks required for milk fat storage, ingredients
Processing batching and cream standardisation; the use of

recombined creams manual tipping operations for batching of powder

ingredients versus automated operations; the type
and efficiency of the recombining technologies
This section provides an introduction to needed; and the size and processing capacity of the
process design, handling raw ingredients, heat treatment and packing units.
recombining dry ingredients, emulsifying
In some cases, having two lines processing the milk fat
milk fat, UHT treatment, cooling and
and powder ingredients in parallel could be a viable
aseptic packing. There is also a brief
solution to meeting higher-capacity demands.
mention of other heat treatment options.

6.4.1
Process design
The design of the recombining process largely depends
on the type of ingredients used. In general, the main
processes and recombining operations are as follows:
• Raw ingredients handling (reception and storage).
• Recombining (batching).
- Rehydration of dry ingredients
(milk powders, stabilisers and thickeners).
- Emulsification of the milk fat source
(AMF, frozen cream).
- Cream standardisation.
• Heat treatment.
- Pasteurisation/Sterilisation.
• Homogenisation.
• Packing and storage.
The unit operations and processing sequences described
above and illustrated in Figure 6.1 are not affected by
the plant capacity. However, the manufacturing capacity
of the plant will influence the:
• Ingredient sources – from 25 kg bags of dry
ingredients and 200 L drums of milk fat, to 1-tonne
(t) powder bins and bulk sources of milk fat.

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EXPERT TIP:
Batching stabilisers, thickeners
and emulsifiers
In most cases, stabilisers and
thickeners are either batched together
with the milk powders, or added

Cream
immediately after their rehydration.
Emulsifiers are batched as part of the
recombining of milk fat sources to aid
their emulsification.

Figure 6.1:
Recombining process for creams (adapted from Tetra Pak, 2020).

1. Mixing tank with heating/cooling jacket

2. High-shear two-speed agitator

3. Thermometer

4. Emptying pump

5. Flow meter

Milk powder
Fat
Cooling medium
Heating medium
Recombined milk
3
Water

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Creams

6.4.2
Raw ingredients –
reception and storage
Milk powders
Recombined creams can use a wide variety of milk
solids. These are typically delivered in a 20 kg to 25 kg
bag format, or less commonly in 1,000 kg bulk bags.
There are some general rules for the handling of all milk
powder ingredients that will ensure the best recombined
cream quality.
• Always follow the manufacturer’s instructions for
storage – typically this will be in a cool, dry storage
area with low relative humidity.
• Store powder off the ground and away from wet
process areas until it is ready to be used in the
recombining process.
• Keep powders away from any hot process
equipment. As well as potential safety risks,
heat-promoted oxidation can cause off-flavours that
will carry into the final recombined cream.

Fat source
The principal component of any recombined cream is
the fat source, with the vast majority coming from dairy
sources such as AMF, cream powder and frozen cream.
Each of these elements needs to be handled differently
to ensure it can be used in cream processing.

AMF
AMF is typically shipped in 200 L drums or 1,000 L
intermediate bulk containers (IBC), e.g. SpaceKraft®.
Although these products can be stored at any
temperature, to reduce oxidation it is best to store
them in a cool, dry area away from direct sunlight.
AMF is a solid at typical ambient temperatures, so
it requires melting before use. For drums, the most
common practice is to have a dedicated ‘warm room’
(45°C to 50°C – see Chapter 3, section 3.1) where they
should be kept before use. Final heating of AMF drums

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Cream
is commonly achieved through the use of heating direct sunlight. As always, it is best practice to follow the
pads, usually set to a temperature of 55°C to 60°C. manufacturer’s recommendations for storage conditions.
SpaceKraft® IBCs contain electrical heating elements
that should be connected to melt the product. Once
melted, the AMF can be pumped into any suitable vessel
6.4.3
ready for use in the recombining process. Recombining dry ingredients
AMF can also be delivered to site in bulk. In this case, it is
Powder rehydration – fundamental principles
transported in tanks at temperatures of about 50°C and
will require a suitable on-site storage facility (see below). A complete rehydration and solubilisation of protein
powders and minor ingredients is a prerequisite to meet
Frozen cream the functional and shelf life attributes of the recombined
product. In general, the powder rehydration process
Frozen cream, or fresh frozen milk fat for recombining
takes place in four stages: wetting, sinking, dispersion
(FFMR), can also be used as the milk fat source for
and dissolution. While these four stages occur in
recombined creams also. It provides a fresh flavour. Such
sequence, they often overlap in different ways depending
products must be stored frozen before use, and must
on the specific properties of the powder and technology
also be melted for use in the recombining process. It is
used (Fang et al., 2008). For further information, see
recommended to use heating plates, and then these
Chapter 3, Figure 3.4.
cartons can be emptied into a transfer tank and pumped
into the recombining process.
Technical levers for powder rehydration
Cream powder In addition to the intrinsic properties of the powder, the
time, temperature and technology used to induct and
Cream powder may be used for recombined cream
disperse the powder will have a major influence on the
manufacture also and should be treated in the same way
efficiency of the recombining process.
as other dairy powders as described above.

In-process storage of fat sources Rehydration temperature and time

Temperature has a strong influence on the rehydration
In some cases there may be such a large quantity of fats,
properties of milk proteins, stabilisers and thickeners.
particularly AMF and non-dairy oils, that dedicated silos
The rehydration temperature for milk proteins varies
are required to store them. These silos should be jacketed
from 10°C to 50°C. As a general rule, the higher the
to maintain a sufficiently high temperature to keep
temperature, the faster the rehydration process and
the fats in liquid form and minimise microbial growth,
the lower the risk of undissolved particles in the batch.
typically > 50°C. As these fats will be stored at elevated
Rehydration times vary from about 24 h at 10⁰C to
temperatures, there is a high risk of oxidation, so any
< 20 min at 40°C to 50°C (Tetra Pak, 2020). Increasing
storage vessel should be nitrogen blanketed.
the rehydration temperature to 50°C is a common
Minor ingredients practice when the dairy powder is difficult to
reconstitute.
As listed above, there is a broad range of minor
ingredients – such as emulsifiers, stabilisers and flavours The temperature and rehydration time used to
– that can be used when making recombined creams. incorporate stabilisers and thickeners are important
Given the wide variety of possibilities, only general rules for creating the final product’s desired properties
can be given here and they are very similar to those for (viscosity, mouthfeel). Temperature not only influences
milk powder storage – store in a cool, dry area away from their dissolution, but also the level of molecular

145
 EXPERT TIP:
Avoiding oxidation and
bacterial growth
To mitigate oxidation issues and
bacterial growth, the recombined
emulsion should not be kept at
high temperature for > 2 h.

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6.
Creams

Cream
entanglements and interactions responsible for their • Probability of lump formation.
thickening and gelling properties (Saha & Bhattacharya, • Level of air incorporation and foaming.
2010). To define the best operating conditions, it is good
practice to understand the specific properties of the Based on the above, it is important to understand the
stabilisers and thickeners used. rehydration properties of the powder (i.e. wettability,
dispersibility, rate of swelling, viscosity development,
Powder recombining technologies tendency and stability of aggregates), as well as the
structures targeted during rehydration. This will define
By influencing the time and efficiency of the rehydration
the best recombining technologies and practices
process, the technology used to induct and disperse
to ensure the optimal efficiency of the process.
the dry ingredients will have a major impact on
the manufacturing cost and performance of the Powder rehydration generally relies on the use of rotor-
final product. stator mixers, also known as high-shear mixers. A wide
range of these mixers is available. Apart from the mixing
In particular, the technology used will determine
head design, the major difference among them is the
the following:
way powders are inducted. In general, they are classified
• Maximum induction rate of the powders into high-shear impeller, batch mixers and in-line mixers.
into the system.
• Rate and efficiency of the powder
dispersion process.

147
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Creams

6.4.4 the emulsifiers are in the system, the dissolved milk

fat and water (or milk) phase are mixed together at a
Milk fat emulsification temperature above the milk fat melting point, usually
about 45°C to 55°C.
Emulsification – fundamental principles
Recombining milk fat into a stable emulsion with a Mixing technologies
narrow distribution of fat-globule sizes is important to: Generally, the mixing technologies for powder
• Ensure a uniform treatment of the product during recombining apply to the emulsification of milk fat
the process. as well. The main difference is that in-line mixers
particularly designed for emulsion applications rely on a
• Meet the desired functional and shelf life attributes
teethed configuration, rather than a blade-screen type.
of the recombined product.
In modern systems, in-line mixers are commonly used for
In the absence of natural milk proteins and
the emulsification of milk fat. The specific design of the
phospholipids, fat-globule physical stability needs
mixer used will depend on whether a single pass through
to be achieved using alternative natural or synthetic
the unit is sufficient to achieve the targeted fat-globule
emulsifiers. The type and amount of emulsifiers used
size. If the efficiency of the in-line disperser is enough to
is important, as they will influence the fat-globule
meet the required globule size in one pass, emulsifiers
size distribution achievable during processing and the
are dissolved in the most suitable phase; both phases are
functional and stability attributes of the final product
heated and dosed in line into the head of the disperser.
while in storage.
If the efficiency of the in-line disperser is not enough
Fat emulsification requires a significant amount of
to meet the required globule size in one pass, then the
energy. Although it is easy to create droplets of oil in
disperser should be placed in a recirculation loop, as
water, making them small enough to prevent separation,
described in section 6.4.3, and the dispersion circulated
flocculation and coalescence requires large amounts
to allow sufficient time to achieve the target fat droplet
of energy. To deform and break up large droplets
size distribution. As with batch mixers, ingredient
into smaller ones, very intense velocity and pressure
addition rates are important to ensure the right
fluctuations need to be applied (Walstra, 1993).
proportion of milk fat and emulsifiers in the head of the
Technical controls for milk fat emulsification mixing unit.

Emulsification temperature and time Cream standardisation

The emulsification temperature is critical for achieving After the emulsion and milk streams have been
good emulsion properties, especially the temperature recombined, they must be mixed in the correct
of the phase at which the emulsifiers are added. The proportions to standardise the cream before
temperature to use for the dissolution of the emulsifiers sterilisation. This typically takes place in a tank or silo
strongly depends on the emulsifier being used, and it with a simple paddle or turbine agitator, and left to
could be as high as 80°C. mix until the mixture is blended homogeneously. After
mixing, the product is ready to transfer for sterilisation
Powder emulsifiers will need to be added and dispersed
and packing.
in one of the phases of the emulsion (either the
aqueous phase or the milk fat phase) using any of the
three technologies described in section 6.4.3. Once

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Cream
EXPERT TIP:
Some UHT creams benefit from
refrigeration.
UHT creams can be stored
at ambient conditions, as the
sterilisation process means food
safety should be maintained
across the shelf life. However,
some creams, such as whipping
creams, maintain optimum
performance if refrigerated early
in their shelf life and kept chilled
until used.

149
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 6
References

Cream
1. Fang, Y., Selomulya C. & Chen, X. (2008).
On measurement of food powder reconstitution
properties. Drying Technology, 26(1), 3–14.
doi.org/10.1080/07373930701780928
2. Tetra Pak. (2020). Dairy Processing Handbook.
Retrieved from https://dairyprocessinghandbook.
tetrapak.com/chapter/recombined-milk-products.
Accessed May 2020.
3. Walstra, P. (1993). Principles of emulsion formation.
Chemical Engineering Science, 48(2), 333–349.
doi.org/10.1016/0009-2509(93)80021-H

151
7.
Formulated
Dairy Beverages
This chapter covers a range of milks
with shelf lives that are longer than
fresh milk. It includes production
considerations that are specific to
each type. The range includes acidic,
premium and protein-enriched milks,
milk teas and coffees, and flavoured
ultra-high-treatment (UHT) milks.

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7

Formulated Dairy Beverages

7.
Formulated
Dairy Beverages

7.1 Avoiding bacteria that germinate at low pH

Acidic beverages There are certain acidophilic (acid loving) bacteria,
thermophilic acidophilic bacteria (TABs) and heat-
resistant mesophile spores (HRMs) that do produce
Although milk is a highly nutritious product, it
spores capable of germinating at low pH (down to
has a natural tendency to spoil. Historically, pH 2.0). Although these are not pathogenic, they are
this meant it had to be consumed very quickly. important spoilage microorganisms.
In the absence of more recent technologies,
such as chilling and pasteurisation, early The minimum growth temperature for these
microorganisms is approximately 8°C and the spores are
attempts to preserve the nutritional value
inactivated by UHT (140°C/4 s). Therefore, they are only
of milk led to the various dairy products that a concern for ambient-stable products that have not
exist today. received a full UHT treatment.

Preserving milk with acids Inactivating heat-resistant moulds and TABs

One method of preserving milk is by fermentation Heat treatments of at least 90°C for 30 s and potentially
with lactic acid bacteria. This converts the lactose in up to 110°C (depending on the ingredient loading) are
the milk to lactic acid, lowering the pH to the point required to inactivate heat-resistant moulds. Higher
where pathogenic bacteria are no longer able to grow. heat treatments are required to inactivate TABs.
Alternatively, acid can be added directly to milk or milk Von Bockelmann and Von Bockelmann (1998) also
protein solutions, eliminating the need for fermentation. provide heat treatment guidance for ambient-stable
This section deals with direct acidified milky beverages acidic beverages.
rather than fermented ones, which are covered in
Chapter 8. How to test for commercial sterility
A pH of 4.6 or less required When testing for commercial sterility, it is important
to use a method that detects viable acid-tolerant
Under acidic conditions (pH ≤ 4.6), pathogenic microorganisms. Standard aerobic plate count (APC)
microorganisms are unable to grow or produce toxins, methods applied to dairy products are not suitable. They
and most bacterial spores are unable to germinate. only detect neutrophilic bacteria, which can grow at
This pH 4.6 upper limit is accepted by regulatory neutral pH but not at the low pH of the acidic beverage.
authorities worldwide. Consequently, acid-tolerant microorganisms that could
The US Food & Drug Administration (USFDA) states, be an issue to the product will not be detected. While no
"An acidified food … has a finished equilibrium pH of 4.6 internationally-accepted standard method exists, using
or below and a water activity (aw) greater than 0.85." either or both of the following may be appropriate:
As C. botulinum and other pathogens cannot grow at a • An acidified agar, such as malt extract agar (MEA)
pH ≤ 4.6, the requirements for thermal processing are acidified to pH 4.5 with malic acid.
less stringent for acidified/acid foods than for neutral
• The Charm EPIC™ system based on adenosine
pH beverages (USFDA, 2021).
triphosphate (ATP) fluorescence.
Acid pH is usually achieved by the addition of weak
undissociated acids, such as lactic acid. This is because
bacterial pathogens are more resistant to strong and
dissociated acids, such as hydrogen chloride (HCl).

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EXPERT TIP:
Sterilise fruit preparations before
use in acidic beverages.

Formulated Dairy Beverages

Bacteria that germinate at low
pH have been found in processed
ingredients such as grains and
fruit extracts. This is why any
fruit preparations used in acidic
beverages should be sterilised (e.g.
by UHT treatment) before use.

7.1.1 protein). Consequently, when the pH is at or below the

isoelectric point for casein (pH approximately 4.6), the
Milky acidic beverages milk separates into insoluble ‘curds’ containing the casein
Liquid skim milk is a colloidal suspension of casein and a yellow liquid (whey) comprising whey proteins and
micelles in an aqueous solution of lactose, minerals and other soluble materials.
whey proteins. The usual pH of milk, around 6.8, is far
above the isoelectric points (net overall charge of zero)
Stabilisers are required to avoid curdling in
of the main milk proteins. Under such conditions, the net acidic beverages
negative charge on the proteins stops them from being When making acid-containing beverages, it is important
brought close enough to interact. This even applies under to use the correct type and level of stabilisers to prevent
the temperatures found in UHT or retort sterilisation. curdling. The most common stabilisers are high methoxyl
(HM) pectin and carboxymethyl cellulose (CMC). Both
Curdling occurs at acid pH are large molecules that carry a strong negative charge.
As the pH drops, however, the charges on the proteins Pectin tends to be seen as a more ‘natural’ ingredient.
are neutralised until the casein proteins begin to There is some suggestion also that beverages made with
interact and fall out of solution (see Figure 7.1). pectin have a better flavour than those made with CMC.
Whey proteins become less soluble at their isoelectric However, CMC tends to be cheaper and is widely used in
points also, but can remain in solution due to their low cost-sensitive markets.
concentration (whey protein is only 20% of the total

Figure 7.1:
Acid precipitation of casein.

- -
Neutral pH - - - -
R1-COO-
-

Far from - - - -

isoelectric point - - - -
-

- - - -
- -
R2-NH2
- -
- + + -
+ - - +
Approaching
isoelectric point - + + -
+ - - +
- -
R1-COOH
+ + + -
-+ +
Isoelectric -
point +-
- R2-NH3+
Low pH + + -
+
-

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Dairy Beverages

At neutral pH, both pectin and CMC are incompatible Homogenising the mixture
with casein as they have similar charge, but at pH
values below the isoelectric point, both pectin and CMC The mixture should then be homogenised to increase
molecules bind to the positively charged caseins and the interactions between the caseins and pectin. A total
prevent them from aggregating (see Figure 7.2). homogenisation pressure of around 100 bar is sufficient
(Tromp et al., 2004). If any fat or cream is used, this
HM pectin and CMC stabilise acidic beverages using should be added before homogenisation as well. After
essentially the same mechanism; so, for simplicity we will homogenisation, other components such as fruit pulps
refer to HM pectin from here on. can be added.

Stabilising low and high protein systems

with pectin
Figure 7.2:
Even at the correct pH, only a relatively small proportion Schematic picture of the ‘replacement’ of ĸ-casein by
of the pectin binds to the casein micelles, but it must be pectin upon lowering the pH and casein micelles coated
present in excess to enable sufficient binding to occur. with adsorbed pectin molecules. Top: low magnification;
In the case of low-protein juice milks, with 5% milk- bottom: high magnification (Tromp et al., 2004).
solids-not-fat (MSNF) or less, the casein suspension is
stabilised by a weak gel of unbound pectin interacting
with the coated micelles. Higher-protein systems
are stabilised entirely by the pectin-covered micelles
themselves with the unbound pectin playing a less
important role (Tromp et al., 2004).
pH 4.0
Hydrating protein solutions and stabilisers
before mixing +
+
pH 6.7 pH 5.5 pH 4.0
When preparing acidic milky beverages, the protein +
+

solutions should be hydrated first in the same way as any +

pH 6.7 pH 5.5 pH 4.0
other dairy beverage. The stabiliser should be hydrated +
separately according to the manufacturer’s instructions
as the presence of ions may interfere with the hydration steric
stabilization
of either pectin or CMC. Once the stabiliser is hydrated,
the stabiliser solution can be mixed with the milk protein
steric
solution and the pH adjusted as soon as possible through stabilization
vigorous mixing.

Adjusting the pH
If the pH is adjusted before adding the stabiliser it may casein micelle casein micelle casein micelle
result in curdling. If the mixture of stabiliser and milk
protein is left too long before pH adjustment, separation
ĸ-casein pectin
between the stabiliser and protein phases may result.
casein micelle casein micelle casein micelle

ĸ-casein pectin

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EXPERT TIP:
Pre-test before using new
flavours and colours.

Formulated Dairy Beverages

Some flavours and colours, especially
those containing acacia gum, may
precipitate the protein – resulting in
a loss of clarity. The mechanism for
this is not well understood, but when
using a new flavour or colour it is
advisable to experiment first, at lab
scale, to make sure the clarity of the
whey protein isolate (WPI) solutions
are not affected.

7.1.2 Dissolving WPI while avoiding foaming

Clear acidic beverages WPI does not require heating to dissolve but is especially
prone to clumping. For this reason, the shear used in
As the name suggests, clear acid beverages are high- recombining should be just enough to disperse the
clarity beverages ranging from near waters (protein level powder in the water without incorporating air. The WPI
of 1% or less) up to sports beverages with protein levels can be pre-blended with carbohydrates, such as sugar
of 7% or more. or maltodextrin, to aid dispersibility. However, this is not
an option in low-calorie beverages such as near-waters.
Choosing the correct protein
Wherever permitted, antifoam should be added to the
The only dairy protein ingredient suitable for use in clear water before the WPI to reduce foaming. For more
acidic beverages is WPI. This is because whey protein information on preventing foaming during recombining,
concentrates contain traces of fat and denatured protein please refer to Chapter 3, section 3.1.2.
(which reduce the clarity) and lactose (which undergoes
Maillard browning). As well as giving the beverage a Electrolytes can reduce clarity
distinct yellow tint, this may affect the brightness of the Electrolytes may result in a loss of clarity in the beverage
colours or even change the colour of the beverage (e.g. also and therefore should be used with care. Sulphates
from blue to green). Ion-exchanged WPI is ideal for this especially should be avoided. Soft water or water
application due to its high clarity and exceptionally low purified by reverse osmosis is recommended.
lactose content.

Stabilisers are not required

This type of beverage does not require stabilisers as the
protein is completely soluble at the pH used – typically
around 3.3 but no higher than 3.5; well below the
isoelectric points of the major whey proteins.

Adjusting the pH
A variety of acids can be used to adjust the pH.
Phosphoric acid works well, either alone or in
combination with citric acid. However, organic acids, such
as citric, lactic and malic, can be used also – either singly
or in blends. The type of acid used can depend on the
type of flavour used in the beverage (e.g. use citric acid
with citrus flavours). An advantage of using an acidic
WPI is that less acid needs to be added during beverage
manufacture, making the final product less sour.
When making clear acidic beverages, approximately
85% of the required acid should be added to the water
before the WPI. Determining the correct amount of
acid to achieve the desired pH may require some
preliminary experiments. If the acid is not added first,
the α-lactalbumin may not dissolve completely, which
will compromise the clarity of the beverage.

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Dairy Beverages

7.2 7.2.1
Premium milks Premium milk benefits
Fresh (pasteurised) milk is consumed all over the world,
Premium milks have a similar flavour profile but the supply is not equally distributed. Fresh milk has
to fresh milk, but a longer shelf life. This a very short shelf life because it is very susceptible to
section discusses the benefits of premium microbial spoilage. Some countries only have a very
milks and outlines how they are made. small milk pool or do not have one at all. The distribution
of milk and dairy products can be challenging in some
countries, especially those with warm climates and
remote areas where shelf life plays an even bigger role.

A similar flavour profile to fresh milk

In countries and areas where local fresh milk supply is
limited or not available, alternatives such as milk powder
and evaporated milk are often used. The flavour of
these alternatives is not the same as the fresh milk they
originated from. Premium milks fill the gap by providing
milk with a similar flavour profile to fresh milk, even in
areas where local fresh milk supply is limited.

Added stabilising ingredients seldom required

Premium milk can be made by mixing a concentrated
milk, such as frozen whole milk concentrate (FWMC), or
a concentrated cream source, such as frozen cream, with
water or skim milk. Premium milks retain the nutritional
properties of fresh milk. They are also ‘clean label’
because normally they do not require any additional
ingredient to stabilise the product. The definition and
the ingredients allowed in premium and fresh milk vary
between countries. Please refer to the local regulatory
guidelines for more information.
The following section describes how FWMC and frozen
cream can be used to make premium milks.

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Formulated Dairy Beverages

7.2.2 The recombining process
Using FWMC to make premium milks When it is used to make a premium milk, FWMC must be
diluted in water. The ratio of water to FWMC depends on
FWMC is a concentrated source of milk made from fresh the total solids (TS) content of the FWMC. For example,
milk. It can be used as an alternative to fresh milk solids. one 10 kg block of FWMC (13% fat, 34% solids non-fat)
Fresh milk is concentrated by removing water; this can be mixed in about 30 kg of water to make 40 kg of
concentrate is quick-frozen then stored and transported whole milk with a typical fat and protein content. The
frozen (see Figure 7.3). It can be used as an alternative composition of a typical FWMC can be found in Chapter 2.
milk source when the local milk supply is low. As it is Figure 7.4 describes the FWMC recombining process for
frozen, it has a longer shelf life than fluid milk. The premium whole milk.
natural goodness and nutritional properties of fresh milk
have been captured by the freezing process.

Figure 7.3:
Production process of FWMC (see Figure 7.4).

Fresh Milk Concentrated Quick Frozen Frozen Whole

Milk Concentrate

159
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Dairy Beverages

Figure 7.4:
Recombining process of FWMC for premium whole milk.

Prepare FWMC

Defrost
Shred
Temper (partially thaw)
Follow your equipment recommendations
at 2ºC–4ºC for maximum 48 h
for handling
(only for small blocks ≤ 10kg)

Disperse in hot water

55ºC–65ºC with agitation
for minimum 20 min

Homogenise
150 or 200 bar first stage and 50 bar
second stage (total 200 or 250 bar pressure)
at 55ºC–60ºC

Liquid Milk
Cool to ≤ 7°C within 60 min if not heat-treated within 30 min
of homogenisation. Hold for no longer than 24 h at ≤ 7°C.

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Formulated Dairy Beverages

Shredding vs thawing Dispersing
To recombine the FWMC, it needs to be either thawed The FWMC needs to be dispersed in water between
before adding it to the water or shredded into small 55°C and 65°C. The water must be at this temperature
pieces to melt in water. A shredder (also known as a to begin with as the temperature will drop when the
shiver, chipper or crusher) can be used to shred the FWMC is added because of its low temperature (-18°C,
product into small pieces very quickly. Thawing the blocks or 2°C to 4°C). Heating and temperature control
takes longer than shredding, requires more refrigerated may be required to maintain the desired recombining
storage space and can only be done with small blocks of temperature. The FWMC needs to mix for at least 20
10 kg or less. FWMC needs to be thawed within 48 h at min in the hot water to enable it to melt and disperse.
2°C to 4°C to minimise the food safety risk and bigger
blocks would require more than 48 h to thaw. Thawing Homogenising
is slow at 2°C to 4°C and therefore the blocks must be After mixing, the now liquid milk can be homogenised. It
spread out. This speeds up the thawing process but also is important that the product is homogenised before it is
requires more refrigerated storage space. heat treated. Homogenisation is required to reduce the
size of the fat globules. This stops fat rising to the top
and creating a cream layer.

Cooling or heat treatment

The recombined milk is then heated to achieve the
required shelf life. If milk is to be held before heat
treatment it can be cooled to ≤ 7°C and held for up to
24 h. Pasteurisation can be used to achieve a shelf life
of up to 14 days, stored chilled. Alternatively, extended-
shelf-life (ESL) processing can be used to extend it to
4 to 6 weeks when stored chilled. UHT heat treatment
can be applied to extend the shelf life to multiple
months at ambient conditions. However, it is advised
to add a stabiliser to prevent creaming or sedimentation
when UHT heat treatment is applied. Note that
increasing the heat treatment from pasteurised to
ESL to UHT will intensify the 'cooked' flavour profile
of the milk. More information on the different heat
treatments can be found in Chapter 4 – Recombined
Milk – Normal Concentration.

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7.2.3 The recombining process

Using frozen cream to make Because frozen cream consists of 42% fat, it needs to be
premium milks mixed with another dairy ingredient, such as fresh skim
milk, and water to create a whole milk with the desired
Frozen cream is a sweet cream with a fat content protein and fat content. The amount of frozen cream can
typical of fresh cream (i.e. 42%). It is pasteurised and be adjusted to make a more indulgent milk with a higher
frozen. Frozen cream can be used to replace fresh fat content. Chapter 6 – Creams – describes the uses of
cream, unsalted butter, anhydrous milk fat (AMF) and frozen cream in the manufacture of cream products.
UHT cream. Just like fresh milk, fresh cream can be
The recombining process of frozen cream is almost
unavailable in some areas or supply can be limited.
identical to that of FWMC except that fresh skim
Unsalted butter, AMF and UHT cream are commonly
milk and water must be used instead of only water to
used to replace fresh cream when supply is not available.
make a premium milk. All the other processing steps
The flavour of these substitutes is different from fresh
and conditions are identical to the FWMC process
cream. Milk made with AMF can be seen as less natural
(see Figure 7.4).
to consumers because it requires the addition of an
emulsifier. Frozen cream does not require an emulsifier
and is therefore regarded as 'clean label'. It also has a
similar flavour profile to that of fresh cream.

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7.3
Figure 7.5:
Protein-enriched beverages Confocal micrograph of UHT milk reconstituted from
WMP to < 4% and > 4% protein. Protein stained green,
This section deals with recombined beverages fat stained red.
containing up to 10% protein but relatively
little added fats, carbohydrates and minerals.
These include sports beverages and ‘on the
go’ meal replacements for people who do not
have time for breakfast or need a
permissible snack.
Single-strength recombined milks (protein and fat up to
3.5%) are covered in Chapter 4, and medical foods are
beyond the scope of this manual.

7.3.1
Using milk protein concentrate (MPC)
Skim milk powder (SMP) or whole milk powder (WMP)
can only be reconstituted to around 3.6% protein due to Recombined milk: 4% protein, 3% fat
the high levels of soluble minerals relative to the protein.
Soluble minerals reduce the heat stability of the milk
leading to fouling or, in extreme cases, aggregation.
Therefore, when milk is reconstituted from WMP and/
or SMP to protein levels higher than 4%, there is a
rapid and extensive aggregation of protein during UHT
treatment (see Figure 7.5).
MPCs contain the same level of soluble minerals as SMP,
but much higher levels of protein. This means that for
a given level of protein, an MPC solution will have much
lower levels of minerals. So, using MPCs in combination
with SMP, WMP or liquid milk allows the protein level
to be raised without unduly increasing the level of
soluble minerals, and also keeping lactose and therefore
calories low. Recombined milk: 5% protein, 3% fat
MPC70 can be used by itself up to 7% protein, but
in combination with milk or milk powders is only
recommended up to 6% protein. MPC85 is recommended
for top-up systems with protein above 6%.

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The recombining process In the case of MPCs, the proportion of casein relative
to lactose is much higher, so the casein micelles form
MPC powders can be recombined in water by the same
stronger and more extensive networks on the surface of
methods detailed in Chapter 3. However, while the
the powder particles. These networks take much longer
primary particles of WMP and SMP dissolve within 20
to fully dissolve (see Figure 7.6), so the primary particles
min at temperatures above 20°C, those of MPCs take
take longer to disappear.
longer for the following reasons.
Although most MPCs contain very little fat, the
Dissolving – why MPCs take longer to dissolve hydrophobic bonds between casein micelles break down
faster in warm water. Mimouni et al. (2009) found that
During the drying process, micelles that come into
MPC 85 dissolved very slowly at 24°C, but far more
contact with each other become bound together by
rapidly at 35°C. For recombining, a water temperature
hydrophobic interactions, both through the micelles
in the range of 50°C to 55°C is recommended to
themselves and by non-micellar caseins (Mimouni et al.,
prevent the growth of pathogens (especially B.
2009). As WMP and SMP contain a large proportion of
cereus and S. aureus) without causing damage to the
lactose, relatively few casein micelles come into contact
proteins. At chilled temperatures (< 10°C) MPCs are
during drying, so the powder dissolves relatively rapidly.
practically insoluble.

Figure 7.6:
Rehydration of MPC powder (Mimouni et al., 2009).

Disruption of
Agglomerates

Primary Powder Release of Material by Disappearance

Particle Erosion of the Surface or Collapse

Persistency of
Vacuole a Network of
Interacting Micelles

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Lactose content and ease of hydration Figure 7.9 shows confocal micrographs of MPC80
The ease with which MPCs can be hydrated depends solutions hydrated at 30°C in an overhead stirrer. After
on the ratio of lactose to protein. Figure 7.7 shows the 30 min, many undissolved primary particles are still
composition of protein powders ranging from WMP visible (stained bright green). However, after 60 min
and SMP to MPC80. The higher the lactose content, the these have disappeared, leaving only globules of residual
more easily water can penetrate the powder and break fat (stained red). In a commercial setting 30 min should
down the networks of casein micelles. Figure 7.8 shows have been sufficient as the MPC would have been
the wettability of powders with protein content ranging exposed to greater shear and higher temperature. This
from 35% (SMP) to 90% (milk protein isolate - MPI). The is in keeping with the work of Crowley et al. (2015), who
higher the protein content, the less wettable the powder found that as the protein content of MPCs increased,
and the more difficult it is to hydrate. their wettability decreased, as did their ability to
rehydrate in water at 25°C.
A hydration time of 20 min at 40°C to 60°C is usually
enough for MPC56 or MPC70, while MPC80 or MPC85
requires 30 min (see Chapter 8, Table 8.2). MPI may
require 60 min or more at 40°C to 60°C.

Figure 7.7:
Composition breakdown of milk protein powders.

100%
90
80
70
Protein
60
Lactose
50
Fat
40 Ash
30 Moisture
20
10
0
WMP SMP MPC 42 MPC56 MPC70 MPC80 WPC80
High-Fat
MPC

Ingredient abbreviations: WPC - whey protein concentrate.

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How to ensure a full milky taste
in high-protein beverages
The lack of soluble, non-protein
components gives MPC solutions
a bland, ‘watery’ taste. While
this may be desirable in some
applications to give a lighter
and more refreshing beverage,
customers usually expect a milky
beverage to have the full body and
flavour of milk.
One way to ensure a milky taste in
a high-protein beverage is to include
SMP or WMP to a normal milk
strength and use MPC to make up
the balance of the protein.

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Dairy Beverages

Figure 7.8:
Water droplets on compressed discs of MPC from MPC35 (essentially SMP) to MPI (MPC90). High
lactose content causes the droplets to spread and consequently lowers the contact angle. The higher
the protein content (and therefore the lower the lactose content), the less wettable the powder. The
contact angle of the droplet on a disc of MPI is similar to that expected for wax or other hydrophobic
substances. From Crowley et al. (2015).

90

80 MPC90 t=0 s MPC90 t=3 s MPC90 t=5 s

70 MPC90
MPC85
MPC80
60

50 MPC70
MPC60

40
MPC50

30
MPC35

20

10
MPC35 t=0 s MPC35 t=3 s MPC35 t=5 s
0
0 1 2 3 4 5
Time (s)

Sensory and functional defects of partial To prevent this type of sedimentation, a sufficiently long
hydration of MPC hydration time with adequate mixing and dispersion
should be allowed for.
By processing the beverage through UHT before
hydration is complete, this effectively fixes the primary Assessing full hydration of the MPC
particles, cross-linking the proteins, which prevents them
from dissolving. These particles are large enough to be One way to assess whether the MPC is fully hydrated
detected in the mouth, giving the beverage a powdery is to measure the particle size distribution. If there is no
or chalky mouthfeel. They are also large enough to sink fat in the formulation, there should be very few particles
rapidly to the bottom of the container as sediment. larger than 0.5 microns in diameter. Figure 7.10 shows
It is recommended to use upstream homogenisation the change in particle size distribution in a solution of
if possible. MPC85 in water at 60°C. After 20 min, much of the

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Figure 7.9: Figure 7.10:

Confocal micrograph of MPC80 after hydration at Hydration of MPC85 in water at 60°C.
55°C. Protein is stained green; fat is stained red.
Note the distinctive ‘bubble’ structure of the primary 6
particles in picture (a), with the protein shell around a 60 min
water-filled vacuole. 5 40 min
20 min
Volume Density (%)

0.001 0.01 0.1 1 10 100 1000 10000

(a) 30 min hydration
Particle Size Class (µm)

The homogenisation step not only reduces the size of the

fat droplets but also breaks up any remaining primary
particles. Homogenisation pressures of 200/50 bar
(250 bar total) are recommended for protein-enriched
beverages. For more detail about homogenisation, see
Chapter 3.

Foaming
(b) 60 min hydration
When air is introduced during the manufacture of
protein-enriched beverages, the proteins tend to
form a stable viscoelastic film around the air bubbles.
MPC has dissolved and the main peak (0.01 to 1 µm) This stabilises them and consequently creates foams
is the free casein micelles. However, there is still a (Sakar & Singh, 2016). Excessive foaming during the
substantial number of primary particles (10 to 100 µm) recombining step can lead to an increase in fouling and a
and agglomerates (approximately 1,000 microns). After shortening of run-times. Ways to prevent foam forming
60 min, all the agglomerates have dissolved and very few during recombining have already been covered
primary particles remain. If it is not possible to measure in Chapter 3.
particle size distribution, hydration of MPC can be
assessed by light microscopy. Extensive foaming can also occur if the packaging
process includes a nitrogen flush step. This is often used
If fat is present, it is impossible to distinguish between to protect oxygen-sensitive ingredients such as vitamins
primary particles and fat droplets without some form of and essential fatty acids, especially docosahexaenoic
microscope. However, the bulk of the particles should be acid (DHA). Bubbling may occur when the gas is flushed
< 2 microns after homogenisation. into the packaging before sealing.

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Table 7.1:
Seven classes of antifoaming agents accepted in foods (Codex Alimentarius, 2019).

INS* No. Food additive or group Acceptable in foods conforming to the following commodity standards
404 Calcium alginate CXS 94-1981 (for use in packing media only)
CXS 117-1981
CXS 70-1981 (for use in packing media only)
CXS 119-1981 (for use in packing media only)
905c(i) Microcrystalline wax N/A
905d Mineral oil, high viscosity N/A
471 Mono- and diglycerides CXS 87-1981
of fatty acids CXS 117-1981
CXS 105-1981
CXS 249-2006
CXS 141-1983
CXS 309R-2011
900a Polydimethylsiloxane N/A
1521 Polyethylene glycol N/A
551 Silicon dioxide, amorphous CXS 105-1981
CXS 117-1981 (anticaking agents in dehydrated products only)
* International Numbering System

If extensive foaming occurs during aseptic packaging Figure 7.11:

of a sterilised beverage, it may ultimately cause issues Filter clogged by an antifoam agent forming a
such as leaks, microbial spoilage, filler malfunction or non-melting greasy gel.
underweight packages. It is important to consider adding
antifoaming agents to the protein-enriched beverages
before packaging to avoid foam formation.

Using antifoaming agents

An antifoaming agent is a food additive that can be
added as a processing aid to protein-enriched beverages
to prevent or reduce foaming during processing. Codex
Alimentarius standards (Codex Alimentarius, 2019)
recognise seven classes of antifoaming agents that can be
added into a food product for this purpose see Table 7.10.

Selecting antifoaming agents for UHT dairy beverages The choice of antifoaming agent for each application
Two types of antifoaming agents commonly used or product category should be discussed with the
in protein-enriched beverages are silicone-based relevant suppliers to tailor it for the development of
antifoams, and mono- and diglycerides of fatty acids. specific formulations. This discussion is also essential for
Both types of antifoaming agents may come in powder, understanding details such as dosage rates and usage
paste or liquid form, depending on the applications. instructions, as well as the economic, environmental,

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and health and safety impacts when applied to the

final product.
7.4
For example, when antifoaming agents are supplied in
RTD milk tea beverages
paste or solid-block form, it is particularly important to
understand the handling instructions and pre-melting
This section is intended to give an overview of
properties before processing. This is to avoid potential the development of near-neutral recombined
issues such as greasy layers forming on filters in the milk beverages using tea flavours and/or tea
UHT processing line (see Figure 7.11). extracts. For more information on the milk
recombining process, please refer to Chapter 3.
Country regulations are another For information on the types of heat processing
important consideration conditions, please refer to Chapter 4.
Different countries also have different regulations
and restrictions on the addition rates and types of
antifoaming agent permitted for use in food products.
7.4.1
For example, silicone-based antifoams, such as Background
polydimethylsiloxane (PDMS), are not permitted
Ready to drink (RTD) milk tea beverages are defined here
for use in Vietnam as a processing aid in food
as tea beverages to which a low amount of milk solids
products. However, mono- and diglycerides of fatty
has been added. They are not usually considered to be
acids antifoams are permitted for use instead. It is
protein-enriched beverages and the tea flavour itself
recommended to consult relevant country regulations
defines the product.
when selecting antifoaming agents.
The most common varieties of tea used in RTD milk tea
drinks are black and green tea (Ferruzzi & Green, 2006).
The tea flavour can be introduced as a brew tea, tea
extract or tea flavour. A sweetened milk reconstituted
with standard milk powders (WMP and SMP), with
typically 2% fat and 5% sugar, can be flavoured with
various types and combinations of ’tea substances’.
These can be chosen to give the desirable milk tea
flavour specific to each region of interest.

Tea flavour added to a dairy beverage

The general approach for RTD milk tea beverage
development is to make a dairy beverage formulation
and add tea flavours and/or tea extracts to it to fulfil
the sensory requirements. Tea flavours can also be
added to a protein-enriched formulation depending on
consumer preferences.

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Tea flavours may alter the milk’s Measuring heat stability of milk protein
heat stability The heat stability of milk protein usually refers to the
Natural tea flavours and extracts usually contain high ability of milk to withstand high processing temperatures
levels of polyphenols, such as catechins. These may alter without visible coagulation or gelation (Singh, 2004).
the heat stability of the milk and tea mixture during heat One common way to assess the heat stability of milk
processing due to their strong interactions with each protein is through the heat coagulation time (HCT)
other (O’Connell et al., 1998). method. The HCT profile is defined as the time it takes
for a sample to coagulate visually under experimental
Perceived health benefits of tea polyphenols conditions that may or may not resemble the
commercial processing conditions.
Tea polyphenols are believed to have beneficial effects
on human health, such as reduced risk of cardiovascular
Tea polyphenols can increase heat stability
diseases. However, the bioaccessibility, bioavailability
and potential health benefit of tea polyphenols in Polyphenol-rich extracts of tea tend to increase the HCT
milk mixtures are still sources of debate, (Van Het Hof overall during heat treatment (Singh, 2004). According
et al., 1998). to O’Connell et al. (1998), the addition of black and green
tea extract to skim milk increases the heat stability as
measured by the HCT–pH profile. Figure 7.12 provides an
7.4.2 example of how adding various tea extracts can affect
Tea polyphenols and milk protein the HCT in a reconstituted milk powder system overall
heat stability (O’Connell et al., 1998).

Tea catechins are water-soluble polyphenol compounds

that contribute to the astringency, bitterness and
antioxidant activity of tea (Haratifar & Corredig, 2014). Figure 7.12:
Effect of green tea extract at 0.4%, w/w, on the
Black tea polyphenols have an affinity for whey protein HCT–pH profile of skim milk, (—●—) control, (-○-) with
whereas green tea polyphenols are associated mostly green tea extract, (X) original pH (O’Connell et al., 1998).
with casein micelles (Ye et al., 2013).
Numerous researchers have reported that the strong
Heat Coagulation Time, min at 140°C

interactions between tea polyphenols and milk proteins

may-affect products from a sensory, stability and health
perspective (Colahan-Sederstrom & Peterson, 2005;
O’Connell et al., 1998; Van Het Hof et al., 1998). For
example, a study conducted by Colahan-Sederstrom and
Peterson (2005) found that adding tea polyphenols could
improve the sensory aspects of beverages by reducing
the 'cooked' flavour found in UHT milk. They found that X

tea polyphenols inhibited Maillard browning during

thermal processing as well.

pH

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Coffee contains polyphenols that break
down into organic acids over time.
This leads to a decrease in pH and
eventually to phase separation. For this
reason, when making RTD coffee beverages
it is generally a good idea to replace some
of the coffee extract with flavour, and
to include neutral buffering salts such as
phosphates or bicarbonates.

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7.4.3
Caffeine levels
Natural tea flavours and extracts usually contain a There are currently no recognised health-based guidance
significant level of caffeine. Therefore, when formulating values for caffeine, but Food Standards Australia New
with tea substances, it is important to understand the Zealand (FSANZ) concluded that there are potential
amount of caffeine and adjust the final dosage rate health concerns regarding the consumption of food
accordingly. Generally, there should be no more caffeine products with caffeine. Figure 7.13 provides a good
in a serving of RTD tea or coffee beverage than in a reference for the typical amount of caffeine to be
standard cup of tea or coffee. consumed for various population groups.

Figure 7.13:
Caffeine levels in common products.
Australian Government-recommended nutritional 2019 guideline for finished goods that contain caffeine
(Food Standards Australia New Zealand, 2019).

Caffeine Levels in Common Products

150

100
Milligrams

50

0
Espresso Formulated Instant coffee Black tea Cola drinks Milk
(145 mg caffeinated 1 teaspoon/ (50 mg (36.4 mg chocolate
caffeine per beverage cup (80 mg per caffeine per caffeine per (10 mg
50 mL cup) or ‘energy’ 250 mL cup) 220 mL cup) 375 mL can) caffeine per
drink (80 mg 50 g bar)
caffeine per
250 mL can)

Under 18 Over 18 Pregnant +

years old years old breastfeeding
No more than 3 mg of caffeine Maximum 400 mg of caffeine Maximum 200 mg of caffeine
per kg in a single serving. per day (all sources). per day (all sources).
E.g. for a 40 kg child 3 mg x 40 Maximum 200 mg in a
kg = 120 mg. single serving.

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7.5 Addition of coffee extracts to a

RTD coffee milk beverages dairy formulation
The general approach to developing a coffee-flavoured
This section gives an overview of the milk is to add water-soluble coffee extracts to a
considerations required for developing dairy base formulation (Ogawa & Cho, 2015). Coffee
near-neutral recombined coffee-flavoured extract is prepared by roasting coffee beans followed
milk beverages using coffee substances by grinding, extracting the soluble compounds (usually
such as coffee powder, coffee extracts and with hot water), then using a series of filtering steps to
coffee flavour. For more information on the remove insoluble material. The targeted total solids (TS)
milk recombining process, please refer to in a typical coffee extract can range from 25% to 60%
Chapter 3. For information on the types of (Farah, 2019) and can be supplied in either liquid (frozen
or ambient) or powder form.
heat processing conditions, please refer to
Chapter 4. Shelf life
The typical shelf life of RTD coffee milk beverages ranges
7.5.1 from 6 to 12 months (Ogawa & Cho, 2015). To achieve
Background this shelf life, some common stability challenges must
be overcome, including acidity development and milk
Coffee beverages come in a variety of packaging types ring formation.
and often contain sugar and milk. In some parts of Asia,
such as Japan and China, RTD coffee milk beverages
are widely consumed and accepted by the population; 7.5.2
however, in Western countries, freshly brewed coffee is Acidity development in RTD coffee
usually consumed instead of RTD coffee milk beverages milk beverages
(Sopelana et al., 2013). The reasons why RTD coffee
beverages are more widely accepted in certain parts of The pH of UHT milk decreases during heat treatment
the world is because they have a long shelf life and are (Salaun et al., 2005) and subsequent storage (Anema,
more affordable than freshly brewed coffee. 2019). However, acidity development in coffee during
storage is more pronounced, even at refrigeration
Protein and milk fat content temperature (Sopelana et al., 2013).
RTD coffee usually has a total protein content of ≤ 3%
and approximately 1% milk fat, forming an oil-in-water
emulsion (Ogawa & Cho, 2015).

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Figure 7.14:
Total chlorogenic acids found in commercial green and roasted coffee beans (Moon et al., 2009).

Colombian
Green

Roasted
Ethiopian

Guatemalan

Mexican

Nicaraguan

Papuan

Sumatran

0 10 20 30 40 50
Amount (mg/g of beans)

Chlorogenic acids in coffee beans A complex reaction

Chlorogenic acid lactones are key components of the A study conducted by Manzocco and Nicoli (2007)
flavour and bitterness in coffee. They are formed during proposed that the gradual pH decrease in coffee is
the roasting process from chlorogenic acids present in a complex reaction and is related to non-enzymatic
coffee beans (Kraehenbuehl et al., 2017). Coffee has browning pathways, such as the Maillard reaction, in
one of the highest concentrations of chlorogenic acids combination with the hydrolysis of esters and lactones
out of all plant constituents (Farah et al., 2005). Levels derived from the chlorogenic acids present
of chlorogenic acid depend on the type of coffee beans in coffee extracts.
and the extraction and roasting conditions, as shown in
Figure 7.14.

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Processing of coffee affects flavour Measuring sourness in coffee beverages

and behaviour Acidity development in coffee beverages is accompanied
Based on this acidity development, coffee substances by a decrease in pH and an increase of sourness, known
added to beverages are unlikely to be inert during as ’coffee staling’. As the pH of the coffee decreases,
storage. The flavour profile and behaviour of coffee the titratable acidity (TA) increases. TA is a measure of
substances in beverages will vary substantially all acidic protons in a sample, including non-dissociated
depending on the initial processing conditions (i.e. bean protons that can be neutralised through the addition of
varieties, extraction and roasting process) used to make a strong base. The increase in TA is regarded as a better
the coffee. Beverage formulations should be specific to indicator of a sourness increase than the decrease in
the flavour targets, so specific trials would be required. pH (Rao & Fuller, 2018). The perception of sourness is
one of the main causes of coffee beverage rejections
(Manzocco & Nicoli, 2007; Sopelana et al., 2013).

Figure 7.15:
Changes in pH over time for four different neutral dairy beverages stored at 30°C.

7.2

7.0

6.8

6.6

6.4

6.2

0
0 2 4 6 8 10 12 14 16
Storage Time (months)

Coffee A Coffee B Non-coffee A Non-coffee B

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Coffee ingredients increase beverage acidity Increasing acidity during shelf life leads to
during shelf life instability in the beverage
Figure 7.15 shows how the pH of four different types The pH decrease in RTD coffee milk beverages tends to
of neutral dairy beverages changes over time. Coffee A lead to phase separation or increased sediment levels
and B samples were coffee milk UHT beverages made over time. This is because casein micelles are depleted in
with the addition of dairy and coffee ingredients. Non- ĸ-casein after UHT processing. They are also more prone
coffee samples A and B were made without adding to aggregate through calcium bridging when the pH
coffee ingredients. of the dairy beverages is lower or ionic calcium reaches
certain critical levels (Anema, 2019).
In a study conducted by Kim et al. (2019), it was also
reported that the inclusion of coffee extracts in RTD The relationships between sediment levels, pH and ionic
coffee milk beverages caused the pH to decrease during calcium levels for UHT milk samples are illustrated in
shelf life storage and this reduced in pH accelerated at Figure 7.16.
higher storage temperatures.
It is noteworthy that Figure 7.16 shows the effect
Based on these results, it is likely that adding coffee of decreasing pH in a plain UHT milk, and when
ingredients to a milk beverage will increase the rate of combined with the pH effects in figure 7.15, there is
acidity development over time. every expectation that acidity development in coffee
milk beverages would make these impacts even
more pronounced.

Figure 7.16:
Relationship between (A): pH and sediment level and (B): ionic calcium and sediment level for all milk
samples: (●) direct UHT milk samples; (○) indirect UHT milk samples; (▽) direct UHT milk sample
with added sodium hexametaphosphate. The inserts show the indirect UHT milk samples on an
expanded scale. (Gaur et al., 2018).

10 A 10 B
0.4 0.4
0.3 0.3
8 8
0.2 0.2
0.1 0.1
0.0 0.0
6 6
6.55 6.60 6.65 1.4 1.6 1.8 2.0

4 4

2 2

0 0

6.6 6.7 6.8 6.9 0.5 1.0 1.5 2.0

pH Ionic Calcium (mM)

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7.5.3 White ring caused by fat globules that may or may

not redisperse
Buffering capacity and use of soluble
The white ring phenomenon is caused by fat globules
salts in dairy beverages that rise over time as they have lower density than the
The pH changes in a dairy beverage are complex. One continuous phase in the beverage system. If the fat
significant factor that affects pH change is the buffering globules are non-flocculated, the fat can be redispersed
capacity of the product itself (Salaün et al., 2005). A during pouring or agitation (Anema, 2019). However,
buffer is an aqueous solution containing an acid and its if the fat flocculates severely, a fat plug or lump of
base that can resist pH changes on addition of an acid fat material may be observed during milk pouring or
or a base. seen floating on the milk after pouring (Anema, 2019).
This type of excessive creaming cannot be redispersed
The buffering capacity in dairy products results from by agitation.
the sum of the buffering capacities of each individual
acid-base group. Increasing the buffering capacity, An example of a white ring is shown in Figure 7.17. The
by adding anions in the form of salts (e.g. phosphate, white ring top layer is mainly composed of fat material
citrate) at neutral pH, may increase the overall buffering and can be formed within several weeks during storage
capacity and minimise the change in pH generally after production.
(Salaün et al., 2005).
A suitable emulsifier may prevent the fat and
protein separation
7.5.4
Comparing the top layer of stable and unstable coffee
White ring formation during storage in milk beverages, as shown in Figure 7.17, shows that the
a UHT coffee milk beverage system protein and fat in the stable system are homogeneously
dispersed in the matrix formed after heat processing.
Creaming is the formation of a fat-rich layer at the The proteins and fats in the unstable system were phase
top of containers of UHT milk beverages (Anema, separated, as shown in Figure 7.17.
2019). Cream layers, also known as white rings, are
a common issue in RTD UHT dairy beverages and are Ogawa and Cho (2015) suggested that selecting a
aggravated by extended storage periods and high suitable emulsifier may delay white ring formation, and
storage temperatures (Anema, 2019). Figure 7.17 shows improve emulsion stability in the coffee milk beverages
what a cream layer looks like in a typical RTD coffee overall. However, it is advisable to consult with ingredient
milk product. suppliers for the best-possible selection of emulsifiers
specific to each formulation developed.
The mechanism for cream layer formation and its
control measures in UHT-processed milk are discussed
in Chapter 4. This section covers the effect of coffee
extracts on white ring formation.

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Figure 7.17:
Representation of a stable and unstable typical RTD coffee milk beverage. The top (a) and bottom (b) layers of the
stable beverage are similar, indicating a homogeneous suspension of protein and fat. There is no white ring on the
top layer. For the unstable beverage, the confocal images of the top layer (c), serum layer (d) and bottom layer (e)
indicate phase separation and white ring formation in the unstable RTD coffee milk over shelf life. White represents
fat. Green represents protein.

Stable Unstable Legend

Fat
(c) Top layer
(White ring layer)

(a)
(d) Serum layer Protein
aggregates

(e) Bottom layer

(b)
Protein

(c) Top layer

(a) Top layer
(White ring layer)

(d) Serum layer

(b) Bottom layer

(e) Bottom layer

179
7.
Formulated
Dairy Beverages

Coffee extracts contain electrolytes Care required when using pure caffeine
Coffee extracts and ingredients contain high amounts Pure caffeine is a hazardous substance and ingestion in
of electrolytes due to the presence of organic acids. A sufficient quantities may cause individuals to experience
lower degree of coffee bean roasting gives an extract toxicity (Willson, 2018). Therefore, care must be taken
containing more electrolytes whereas a higher degree of when using pure caffeine, both for the safety of the
roasting means less electrolytes in coffee extract (Moon workers and to ensure the levels of caffeine in the final
et al., 2009). beverage do not exceed regulatory and toxicity limits.
The general recommended amount of caffeine for
Electrolytes can destabilise milk healthy adults is ≤ 400 mg per day (Willson, 2018). For
coffee beverages more detail, see Figure 7.13.

Ogawa and Cho (2015) speculated that the electrolytes

in coffee extracts influence the emulsion stability
when using various types of emulsifiers. This makes
the emulsion unstable and eventually causes the milk
ring formation.
They also reported that coffee milk beverages become
more unstable as the content of coffee extract increases,
ultimately contributing to the formations of milk ring
in the product. However, adding coffee ingredients
is critical for the unique rich coffee flavour profile
they provide.

Using artificial coffee flavour with caffeine

powder to improve stability
Similar to tea, coffee ingredients usually contain
high levels of caffeine. Caffeine is well known as one
of the main contributors to the bitterness in coffee
(Kraehenbuehl et al., 2017). One way to reduce
the amount of coffee substances in a coffee milk
beverage (and therefore improve its stability) without
compromising the flavour is to use anhydrous caffeine
powder in combination with various types of artificial
coffee flavour.

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 7
EXPERT TIP:
Always ensure that cocoa powder is
properly hydrated as a slurry before

Formulated Dairy Beverages

mixing into the batch; otherwise,
bacterial spores can be protected
within lumps of dry powder and
survive the UHT process.
It is not necessary to cook the cocoa
slurry, but it should be hydrated at
around 60°C to ensure that any cocoa
fat is fully melted.

7.6 7.6.3
UHT-processed flavoured milk The challenges of
chocolate-flavoured product
Several factors need to be considered when
Chocolate is the most popular flavour worldwide,
selecting flavour compounds for use in and chocolate-flavoured product is one of the most
UHT milks. challenging to make.

7.6.1 Quality cocoa key to success

Controlling pH A good grade of cocoa powder should be selected.

Cutting costs by using an inferior grade of cocoa powder
Some flavourings, particularly some berry-fruit flavours, is not advised, as good-quality cocoa is the key to
alter the pH of the milk, which may lead to excessive producing a successful chocolate milk. Like coffee, cocoa
UHT-plant fouling and may cause sediment in the final is naturally acidic, so alkalised cocoa powder should
product. If such a flavour is chosen, it may be necessary always be used.
to neutralise the milk back to the normal pH. Phosphate
As well as having the desired flavour characteristics,
salts are recommended as a first choice for this pH
it should have a low count of bacterial spores (normal
correction – disodium monohydrogen orthophosphate
cocoa powder has a high count).
(DSP) for an alkaline shift and monosodium dihydrogen
orthophosphate (MSP) for an acid shift. As the cocoa particles are not soluble, the cocoa powder
should be ‘superfine’ so there is less tendency for the
particles to settle on the bottom of the carton or bottle
7.6.2 and also to avoid powdery mouthfeel.
Flavour stability during
UHT processing Stabiliser selection is important
Stabiliser compounds are required to hold the cocoa
Any chosen flavour must be stable to the UHT process in suspension. Most of these contain some form of
and not destroyed at the high temperature. ĸ-carrageenan, among other components, and form
a fragile gel-like structure by interacting with the milk
Flavour compound loss in a direct-steam-heating
proteins. This structure remains intact while the milk is
UHT plant
undisturbed, holding the cocoa particles in its network.
Another frequent problem is loss of volatile flavour However, it breaks down as soon as the milk is gently
compounds in the vacuum flash-cooling process when shaken or disturbed in the act of drinking giving it a
direct steam heating is being used. It may not always pleasantly creamy mouthfeel without being too thick. It
be satisfactory to use more flavouring, particularly if a is important to choose an effective stabiliser and follow
multi-component flavour preparation is used. In such a the supplier’s advice on its use.
case, the solution is either to find a more suitable flavour
compound or to use an indirect UHT plant.

181
References

1. Anema, S. G. (2019). Age Gelation, Sedimentation 8. Food Standards Australia New Zealand. (2019).
and Creaming in UHT Milk: A Review. Comprehensive Caffeine. Retrieved 29 October, 2020, from
Reviews in Food Science and Food Safety. https://www.foodstandards.govt.nz/consumer/
doi.org/10.1111/1541-4337.12407 generalissues/Pages/Caffeine.aspx
2. Codex Alimentarius. (2019). Antifoaming 9. Gaur, V. Schalk, J. & Anema, S. (2018). Sedimentation
agents. Retrieved 1 July, 2020, from https:// in UHT Milk. International Dairy Journal 78, 92−102.
www.fao.org/gsfaonline/additives/results. doi.org/10.1016/j.idairyj.2017.11.003
html?techFunction=3&searchBy=tf
10. Haratifar, S. & Corredig. M. (2014). Interactions
3. Colahan-Sederstrom, P. M. & Peterson, D. G. (2005). between tea catechins and casein micelles and their
Inhibition of key aroma compounds generated during impact on renneting functionality. Food Chemistry,
ultra-0high-temperature processing of bovine milk 143, 27–32. doi.org/10.1016/j.foodchem.2013.07.092
via epicatechin addition. Journal of Agricultural and
11. Kim, G. Y., Lee, J., Lim, S., Kang, H., Ahn, S., Jhoo, J. W.
Food Chemistry, 53(2), 398–402. doi.org/10.1021/
& Ra, C. S. (2019). Effect of antioxidant addition on
jf0487248
milk beverage supplemented with coffee and shelf life
4. Crowley, S. V., Desautel, B., Gazi, I., Kelly, A. L., prediction. Food Science of Animal Resources, 39(6),
Huppertz, T. & O’Mahoney, J. A. (2015). Rehydration 903–917. dx.doi.org/10.5851%2Fkosfa.2019.e76
characteristics of milk protein concentrate powders.
12. Kraehenbuehl, K., Page-Zoerkler, N., Mauroux, O.,
Journal of Food Engineering 149, 105−113. doi.
Gartenmann, K., Blank, I. & Bel-Rhlid, R. (2017).
org/10.1016/j.jfoodeng.2014.09.03
Selective enzymatic hydrolysis of chlorogenic
5. Farah, A. (2019). Coffee: Production, Quality and acid lactones in a model system and in a coffee
Chemistry. Royal Society of Chemistry. Retrieved extract. Application to reduction of coffee
from https://www.fda.gov/food/guidance- bitterness. Food Chemistry, 218, 9–14. doi.org/
documents-regulatoryinformation-topic-food-and- 10.1016/j.foodchem.2016.09.055
dietary-supplements/acidified-low-acid-canned-
13. Manzocco, L. & Nicoli, M. C. (2007). Modelling the
foods-guidancedocuments-regulatory-information.
effect of water activity and storage temperature
Accessed 8 July 2020.
on chemical stability of coffee brews. Journal of
6. Farah, A., De Paulis, T., Trugo, L. C. & Martin, P. R. Agricultural and Food Chemistry, 55(16), 6521–6526.
(2005). Effect of roasting on the formation of doi.org/10.1021/jf070166k
chlorogenic acid lactones in coffee. Journal of
14. Minoumi, A., Deeth, H. C., Whittaker, A. K., Gidney,
Agricultural and Food Chemistry, 53(5), 1505–1513.
M. J. & Bhandari, B. R. (2009). Rehydration process of
doi.org/10.1021/jf048701t
milk protein concentrate powder monitored by static
7. Ferruzzi, M. G. & Green, R. J. (2006). Analysis of light scattering. Food Hydrocolloids 23(7), 1958−1965.
catechins from milk-tea beverages by enzyme- doi.org/10.1016/j.foodhyd.2009.01.010
assisted extraction followed by high-performance
15. Moon, J. K., Hyui Yoo, S. U. N. & Shibamoto, T. (2009).
liquid chromatography. Food Chemistry, 99(3),
Role of roasting conditions in the level of chlorogenic
484–491. doi.org/10.1016/j.foodchem.2005.08.010
acid content in coffee beans: Correlation with coffee
acidity. Journal of Agricultural and Food Chemistry,
57(12), 5365–5369. doi.org/10.1021/jf900012b

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16. O’Connell, J. E., Fox, P. D., Tan-Kintia, R., & Fox, P. F. 24. USFDA. (2021). Title 21: Food and Drugs PART
(1998). Effects of tea, coffee and cocoa extracts on 113—THERMALLY PROCESSED LOW-ACID
the colloidal stability of milk and concentrated milk. FOODS PACKAGED IN HERMETICALLY SEALED
International Dairy Journal, 8(8), 689–693. CONTAINERS. Retrieved from: https://www.ecfr.gov/
doi.org/10.1016/S0958-6946(98)00105-8 cgi-bin/text-idx?SID=3f0300d2be3c074366e396eac
82a5a67&mc=true&node=se21.2.113_13&rgn=div8.
17. Ogawa, A. & Cho, H. (2015). Role of food emulsifiers
Accessed 9 July 2021.
in milk coffee beverages. Journal of Colloid and
Interface Science, 449, 198–204. doi.org/10.1016/j. 25. Van Het Hof, K. H., Kivits, G. A. A., Weststrate, J. A.
jcis.2015.01.063 & Tijburg, L. B. M. (1998). Bioavailability of catechins
from tea: The effect of milk. European Journal of
18. Rao, N. Z. & Fuller, M. (2018). Acidity and Antioxidant
Clinical Nutrition, 52(5), 356–359. doi.org/10.1038/
Activity of Cold Brew Coffee. Scientific Reports, 8(1),
sj.ejcn.1600568
1–9. doi.org/10.1038/s41598-018-34392-w
26. Von Bockelmann, B. & Von Bockelmann I. (1998).
19. Salaün, F., Mietton, B. & Gaucheron, F. (2005).
Long-life products: heat-treated, aseptically packed:
Buffering capacity of dairy products. International
a guide to quality. Ajarom Sweden. ISBN 91-630-
Dairy Journal, 15(2), 95–109. doi.org/10.1016/
6695-5.
j.idairyj.2004.06.007
27. Willson, C. (2018). The clinical toxicology of caffeine:
20. Sarkar A., Singh H. (2016) Emulsions and Foams
A review and case study. Toxicology Reports, 5,
Stabilised by Milk Proteins. In: McSweeney P.,
1140–1152. doi.org/10.1016/j.toxrep.2018.11.002
O'Mahony J. (eds) Advanced Dairy Chemistry.
Springer, New York, NY. doi.org/10.1007/978-1-4939- 28. Ye, J., Fan, F., Xu, X. & Liang, Y. (2013). Interactions
2800-2_5 of black and green tea polyphenols with whole
milk. Food Research International, 53(1), 449–455.
21. Singh, H. (2004). Heat stability of milk. International
doi.org/10.1016/j.foodres.2013.05.033
Journal of Dairy Technology, 57, 111−119. doi.org/
10.1111/j.1471-0307.2004.00143.x
22. Sopelana, P., Pérez-Martínez, M., López-Galilea,
I., de Peña, M. P. & Cid, C. (2013). Effect of ultra-
high temperature (UHT) treatment on coffee brew
stability. Food Research International, 50(2), 682–
690. doi.org/10.1016/j.foodres.2011.07.038
23. Tromp, R. H., de Kruif, C. G., van Eijk, M. & Rolin,
C. (2004). On the mechanism of stabilization
of acidified milk drinks by pectin. Food
Hydrocolloids, 18(4), 565−572. doi.org/10.1016/j.
foodhyd.2003.09.005

183
8.
Cultured
Products
This chapter provides an overview of
generic cultured product categories.
They each contain a wide range of
varieties, too numerous and diverse
to cover in this manual.

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8

Cultured Products
8.
Cultured Products

8.1 8.2
Introduction What is yoghurt?
Every society that has kept animals for There are many definitions for cultured products and
each country has its own regulations or guidelines for
milk has developed cultured or fermented
manufacturing these products. They are usually aligned
foods to preserve food and minimise with the Codex standard for fermented milks. In this
lactose-intolerance issues. Numerous manual, the terms ‘cultured’ and ‘fermented’ are used
cultured products have been developed over interchangeably with the same meaning.
time, using milk from a variety of animals,
such as cows, sheep, goats, camels, horses Codex fermented milk description summaries
and reindeer. The content in this section is (Codex, 2018)
based on cow's milk. Table 8.1 outlines a few different fermented milks
Manufacturing cultured products from recombined milk defined by their starter culture, and Table 8.2 shows the
is very similar to their manufacture from fresh milk. typical compositions of cultured food products.
Protein ingredients are often added to fresh milk as a Fermented milk: "A milk product obtained by
cost-effective way to increase its protein. fermentation of milk … by the action of suitable
microorganisms and resulting in the reduction of pH
with or without coagulation (isoelectric precipitation).
These starter microorganisms shall be viable,
active and abundant in the product to the date of
minimum durability."

Table 8.1:
Fermented milks defined by their fermentation starter culture. Certain fermented milks are characterised by the
specific starter culture(s) used for fermentation.

Yoghurt Symbiotic cultures of Streptococcus thermophilus and Lactobacillus delbrueckii

subsp. bulgaricus.
Alternative culture yoghurt Cultures of Streptococcus thermophilus and any Lactobacillus species.

Acidophilus milk Lactobacillus acidophilus.

Kefir Starter culture prepared from kefir grains, Lactobacillus kefiri, species of the genera
Leuconostoc, Lactococcus and Acetobacter growing in a strong specific relationship.
Kefir grains constitute both lactose-fermenting yeasts (Kluyveromyces marxianus) and
non-lactose-fermenting yeasts (Saccharomyces uniporus, Saccharomyces cerevisiae and
Saccharomyces exiguous).
Kumis Lactobacillus delbrueckii subsp. bulgaricus and Kluyveromyces marxianus.

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Cultured Products
Table 8.2:
Typical compositions of cultured foods.

Standard yoghurt Greek yoghurt Petit suisse or Yoghurt drinks Fermented milk
(stirred/set/ quark drinks (FMDs)
ambient)
Protein (%) 3–5 5 – 10 5 – 20 2 – 10 approx. 1

Fat (%) 0–5 0 – 10 0 – 15 0–3 –

Total solids (%) 10 – 20 20 – 25 10 – 40 10 – 20 10 – 20

Concentrated fermented milks: "… fermented milk, the Drinking yoghurt

protein of which has been increased prior to or after
fermentation to a minimum 5.6%." This is a fermented milk product that is consumed as
a liquid. There are several variants. The yoghurt milk
Flavoured fermented milks: "… composite milk can be fermented and then either sheared to give the
products … which contain a maximum of 50% of desired viscosity or diluted with a liquid (usually sugar)
non-dairy ingredients." stream. The viscosity can vary widely, depending on the
product type and market. The process used will depend
8.2.1 on specific markets’ taste preferences. Depending on
the market, drinking yoghurts can have protein contents
Standard yoghurt types ranging from 1% to 2% to > 6%.
Stirred/spoonable yoghurt Fermented milk drink (FMD)
This is a fermented milk product that is normally In fermented milk drinks the dairy components have
consumed using a spoon. The product is fermented undergone high-heat treatment before fermentation
in bulk, stirred/smoothed and then filled in the final (e.g. 98°C for 100 min), to create desired flavours and
packaging. Stirred yoghurt typically has a smooth, thick, colours. The (probiotic) bacterial cell counts are often
yet flowing, consistency. high in these drinks and therefore fermentation can be
long: up to 7 days. Yakult is perhaps the best-known
Ambient yoghurts
example of a FMD.
Ambient yoghurts are long-life variants of stirred
yoghurts. They are particularly popular in China where Set yoghurt
they saw phenomenal growth over 5 to 10 years leading This is a fermented milk product that is fermented in the
into 2020. This type of yoghurt can have a shelf life of up final retail packaging. The yoghurt gel has a firm texture
to 10 months at room temperature. and holds its shape after being cut with a spoon.

187
8.
Cultured Products

8.3 1. Ingredient recombination (typically at ~50°C). The

ingredients will include milk/milk powders/water, fat
Generic yoghurt process source (cream or anhydrous milk fat – AMF), sugars,
protein concentrates (whey protein concentrate
Figure 8.1 shows the generic flow diagrams for different – WPC, milk protein concentrate – MPC) and
yoghurt products. sometimes stabilisers.
2. Homogenisation (two stages 150/50 bar, typically
8.3.1 at approximately 60ºC).
Chilled yoghurts 3. Heat treatment (typically 95°C for 5 min).
4. Cooling to fermentation temperature (i.e. 41°C).
The traditional chilled yoghurt processes have several 5. Inoculation.
common steps:
Then the processes differ for different chilled
yoghurt types.

Set Yoghurts Stirred Yoghurts Drinking Yoghurts

The inoculated milk is filled The inoculated milk is The inoculated milk is
into individual retail containers fermented in bulk until the pH is fermented in bulk until the pH is
(pottles), sometimes with an < 4.6, typically 4.2 – 4.1. < 4.6, typically 4.2 – 4.1.
added fruit layer on the bottom.
Cooled to approx. 20°C. Cooled to approx. 20°C.
The milk is fermented in these
pottles until the pH is < 4.6, The gel is broken and smoothed The gel is broken and either
typically 4.2 – 4.1. to remove lumps and vigorously sheared to give the
packed into retail containers, desired viscosity or diluted with
Cooled before distribution. sometimes with added fruit a cooled, pasteurised mixture
pieces or fruit pulp and flavours. of sugar, water and pectin to
the desired viscosity and protein
content (typically 1% –2%).

The diluted mix is then

packed into retail containers,
sometimes with fruit or flavour
addition.

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Cultured Products
8.3.2
Ambient yoghurts
The ambient yoghurt process is largely the same as for
stirred yoghurts with an added heating step, as well as
different stabiliser choices and addition points:
1. Ingredient recombination (typically at approximately
50°C). The ingredients will include milk/milk
powders/water, fat source (cream or AMF), sugars,
protein concentrates (WPC, MPC) and selected
stabilisers.
2. Homogenisation (two stages 150/50 bar, typically
at approximately 60ºC).
3. Heat treatment (typically 95°C for 5 mins).
4. Cooling to fermentation temperature (i.e. 41°C).
5. Inoculation.
6. Bulk fermentation until the pH is less than 4.6,
typically 4.2 to 4.1.
7. Mixing/gel breaking.
8. Cooling to approximately 20°C.

Then the processes differ as follows:

Ambient Stirred Yoghurts Ambient Drinking Yoghurts

• Smoothing. • Mix sugar and possible stabilisers.

• Possible fruit/flavour addition. • Recombine at 70°C–80°C.
• Heat treatment (typically 75°C for 25 s). • Mix with yoghurt.
• Possible aseptic fruit/flavour addition. • Homogenise.
• Aseptic packaging. • Possible fruit/flavour addition.
• Heating (95°C–110°C).
• Aseptic packaging.

189
 Figure 8.1:
Generic flow diagrams for different yoghurt products.

Milk Ingredient Selection

Treated Water
Whole Milk Powder (WMP)
Skim Milk Powder (SMP)
Recombine Ingredients
Protein Sources (Milk Protein Concentrate – MPC/
at approx. 50°C
Whey Protein Concentrate –WPC)
Fat Sources (Cream/Anhydrous Milk Fat – AMF)
Sugars
Homogenise approx.
Stabilisers
150/50 bar at 50°C–60°C
Flavour Selection

Heat Treat approx.

95°C for 5 mins

Cool to Inoculation
temperature approx. 41°C

Possible Culture
Inoculate
Treated Water Selection

Possible Sugar
Stabilisers

Ferment approx. with or Packing in

41°C in Tanks without Commercial
fruit/flavour Packs
Ingredient
Selection Gel Breaking
Ferment at
approx. 41°C
Recombine Cool to approx. 20°C

Cool
Mixing

Homogenisation Smoothing

fruit/flavour fruit/flavour

Heating Packing Packing Heating 75°C for 25 s

95°C–110°C
Or Asceptic
fruit/flavour

Aseptic Aseptic
Packing Packing

Ambient Chilled Chilled Ambient Set

Drinking Drinking Stirred Stirred Yoghurt
Yoghurt Yoghurt Yoghurt Yoghurt

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 8
8. EXPERT TIP:
pH probe accuracy

Cultured Products
A good pH probe typically has an
accuracy of ± 0.1 units; for a bad
probe, ± 0.2 units is more likely.

Cultured Products
8.3.3 To maintain a good-quality product, the yoghurt needs
to be stored at a temperature of 4°C, i.e. chilled yoghurt.
Ensuring food safety and preventing This low temperature helps prolong the shelf life of
microbial spoilage the product from a few days at ambient conditions
to several weeks. If the product is clean, a shelf life of
Chilled yoghurts approximately 42 days can be expected, provided the
If yoghurt preparation and packing practices are product is stored at or below 4°C. Some culture suppliers
poorly controlled, product may be subject to microbial will happily provide products that will inhibit yeast and
contamination, resulting in spoilage. Chapter 3 and mould growth, extending the shelf life to even 60 days.
other parts of this manual cover best practice and issues
Ambient yoghurts
relating to recombining ingredients and will not
be repeated here. As the name suggests, ambient yoghurts can be
stored at ambient conditions for many months. This is
The recombined and homogenised yoghurt milk has a
achieved by giving the finished product a heat treatment
heat treatment of (typically) 95°C for 5 min. This heat-
immediately before packing. This heating (see section
treatment step serves to kill any vegetative bacteria that
8.3.2) serves to make the yoghurt commercially sterile.
might be present in the yoghurt milk. The heat treatment
When aseptically packed in sterile packaging, a shelf
also causes the whey proteins to denature and bind
life of up to 10 months can be expected. However, the
with casein to optimise gel firmness in the final yoghurt
integrity of the product is dependent on the quality of
structure. It is essential that all vegetative bacteria are
the heating and the packing systems.
killed before the yoghurt culture is added. Fermentation
at approximately 41°C in a milk that has high water The heat treatment is necessary to control the risk of
activity and a large amount of food (lactose) is an ideal spore-forming acid-tolerant microorganisms surviving
environment for microorganisms to grow. If undesirable the process and being able to grow at ambient
bacteria were to grow, competing with the main culture temperatures in the final product. Of particular
for the available lactose and slowing fermentation, then importance are the heat-resistant yeasts and moulds.
the product would be spoilt before packing. This also These fungi may enter the yoghurt manufacturing
explains why all the ingredients are added prior to the process from either the ingredients (dairy and/or non-
heat treatment step and not after. dairy ingredients) or during packing. Heat-resistant
yeasts are killed by processing temperatures > 90°C;
Acid conditions are critical for maintaining a safe
however, the heat-resistant moulds require heat
product. Low pH is essential and, when combined
treatments of at least 95°C to 110°C.
with the chilling in the final product, this provides the
microbiological hurdles that prevent contamination. As the heat-resistant moulds are unable to grow at
A pH value of 4.6 is considered the maximum as temperatures < 8°C, they are only an issue for the
pathogenic bacteria do not grow at pH values below ambient-stable products, i.e. not refrigerated yoghurts.
this level. The common preference is for a pH of < 4.4.
This allows a safety margin for calibration errors and
other inaccuracies in pH-measuring equipment. At
these conditions, the key organisms that can grow are
yeasts and moulds. These are unlikely to be present if
the equipment is clean and the processing rooms are
clean. If present, the most likely addition point is in the
packing line.

191
8. EXPERT TIP:
Disperse ingredients thoroughly

Cultured Products
before heat treatment.
The heat treatment in the yoghurt
process is sufficient to dissolve the
ingredients, so it is important to
ensure they are well dispersed before
heat treatment.

8.4 Hydration when recombining milk powders

Best practice for recombining When reconstituting standard milk powders (WMP
and SMP) the basic colloidal structure of the protein
and dispersion becomes established very quickly, within 20 min or less
at 20°C, although a recombining temperature of 40°C
The protein content of some milk sources can to 55°C is preferable. As the recombining process itself
be low – leading to weak yoghurt gels. Protein often takes longer than 20 min, there is seldom a need
ingredients are frequently used to increase or to make special provision for a hydration period.
standardise the protein and solids content. Chapter 3, section 3.1, of this manual provides a more
detailed explanation of recombining and hydration.
Other ingredients can also be added to
optimise the final product’s taste (e.g. sugar) Reconstitution temperature vs MPC
and texture (e.g. starch or other thickeners). protein level
The additional ingredients are recombined into fresh milk We recommend higher reconstitution temperatures
or recombined milk (i.e. WMP and water). for MPC ingredients. For example, MPC56 and MPC70
require a minimum 20 min hydration at 40°C to 60°C,
High shear is generally required
and MPC85 requires a minimum of 30 min hydration at
Milk proteins and some stabilisers are hygroscopic 40°C to 60°C (see Table 8.3). Chapter 7, section 7.3.1,
(absorb moisture from the air) and generally require has more information on recombining MPCs.
high shear for dispersion and mixing. Many yoghurt
manufacturing problems relating to added proteins
are due to inappropriate dispersion of the powders.
Table 8.3:
These issues can easily be overcome by using the right Typical hydration time of MPCs*.
equipment type or conditions (e.g. addition rate, mixing
time and temperature). There are many types of
MPCs < 20°C 20°C–40°C 40°C–60°C
equipment available for this part of the operation. They
include the pump and funnel, venturi disperser, Ytron- MPC56 > 30 min > 30 min ≥ 20 min
type mixers, Fristam mixers, Cowles dissolver, tri-blender
MPC70 > 30 min > 30 min ≥ 20 min
and liquiverter.
Air inclusions can be a problem and should be avoided. MPC85 > 60 min > 30 min ≥ 30 min
See Chapter 3, section 3.1.2, for suggestions to Functional MPC70s > 30 min > 20 min ≥ 20 min
minimise foaming.
Functional MPC85s > 30 min > 30 min ≥30 min
Some MPCs have specific
MPI ** > 60 min > 60 min
recombining conditions
*Indication of time required for hydrating/suspending MPCs within each
Some standard MPCs and functional MPCs have temperature range is based on the assumption there is sufficient shear
to adequately disperse the MPCs.
properties that require special recombining conditions,
**Hydration at < 20°C is not recommended for MPI.
such as more sophisticated dispersion equipment,
or longer holding times for hydration or activation.
Some may require a specific order of addition to
create or avoid interactions with other components in
a formulation.

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EXPERT TIP:
Protein reconstitution temperatures
> 60°C are not recommended.
They may induce reactions
between some of the proteins, and

Cultured Products
temperatures > 70°C are unsuitable
as they denature the whey protein
component of an MPC powder,
which leads to changes in some
functional properties.

8.5 Figure 8.2:

Other yoghurt and Strained and quick processes for manufacture of high

cultured products
protein yoghurt

8.5.1 Strained Process

High-protein yoghurt products Milk
↓
The main difference between the standard yoghurts Homogenisation
and the concentrated products is the elevated protein ↓
Heat treatment
and solids content. They are typically produced by either ↓
the strained or direct process. Figure 8.2 shows the two Cool
processes used to make high-protein yoghurt. ↓
Ferment at approx. 42°C
Processes ↓
Separation Step
↓ Whey
Strained process
Curd
The yoghurt milk is fermented as described above ↓
(section 8.3). At a pH of 4.5 to 4.6, the curd is stirred, and Cool
the whey removed using separators (or ultra-filtration ↓
Fruit addition (optional)
membranes) to increase the total solids to the target ↓
composition. During the separation step, around 50% to Filling
75% of the cultured milk is ‘lost’ as an acidified liquid-
whey waste stream. The concentrated curd can be left
plain or mixed with cream and sweet or savoury flavours
before filling into retail containers.
Quick Process
Direct set quick process
This process increases milk solids during recombining at Milk + milk protein + cream (optional)
the start of the process, rather than by concentrating ↓
Homogenisation
after fermentation. This is achieved by adding MPC, ↓
WPC, or functional WPC to the milk depending on Heat treatment
target protein content and texture. As a result, existing ↓
Cool
yoghurt manufacturing equipment can generally be ↓
used, eliminating the need for major capital investment Ferment at approx. 42°C
and avoiding the acid whey waste stream generated ↓
Cool
during the traditional strained process. Cream and sugar
↓
can be added to the milk before culturing, as the target Fruit addition (optional)
composition will be maintained by eliminating the whey ↓
removal step. Filling

193
8.
Cultured Products

Products and sometimes rennet. The texture is thick, smooth and

creamy, and the product is typically eaten as a dessert or
Greek yoghurt snack. These products come with varying fat and protein
Traditional Greek yoghurt is essentially a spoonable contents and are sold plain, or sweetened and fruited, or
yoghurt with the added step of concentration after as savoury versions with salt or herbs.
fermentation. Historically this was achieved by filling
Labneh or labaneh
muslin bags with yoghurt and draining the whey. In some
artisanal processes, this is the preferred technique. At Labneh is a product of Middle Eastern origin and very
industrial scale, large centrifugal nozzle separators are similar to Greek yoghurt but typically much higher in fat.
used to remove the whey. Greek yoghurts are frequently This yoghurt is concentrated by removing whey through
made using the more efficient direct or quick process a cloth filter, although centrifugal separators are now
(see Figure 8.2). used for large-scale production. Labneh has a paste-like
consistency and is used as a spread. The fat content can
Petit suisse, fromage frais and quark be quite variable, and some products are very similar to
Petit suisse, fromage frais and quark are similar types cream cheese. It can also have a higher salt content than
of products. They can be described as soft, cultured, other cultured products.
unripened fresh cheese made using a mesophilic culture,

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Curd 8.5.2
Curd is a traditional Sri Lankan and Indian product. Other cultured products
Legally, there are two standards for curd in Sri Lanka,
one for buffalo milk product (8% fat) and the other for Besides drinking yoghurt, there are many regionally
cow milk product (5% fat). Traditionally, buffalo milk important liquid cultured or sour milk drinks including
is used and fermented in a clay pot. Any whey that is acidophilus milk, ayran, cultured buttermilk, dhoog, kefir,
produced ‘filters’ through the porous clay. A multi-strain laban, lactic acid drinks and lassi.
starter is used, and fermentation takes place in sunlight.
The fermentation takes almost two days and the
resultant product is a firm, very acid curd. The traditional
product has a thick layer of fat on top as the milk is
not homogenised.

Cottage cheese and paneer (queso blanco, hoop cheese,

farmer cheese or pot cheese)
Cottage cheese and paneer are often classified as
cultured or fresh cheese curd. They are mild in flavour
when the whey is removed after acidification (i.e. curd
formation) by lactic acid bacteria and/or lactic acid.
Cottage cheese is strained, and the curds are cooked
before being washed to remove more acidity. If the curd
is then pressed it may be called paneer, queso blanco,
hoop cheese, farmer cheese or pot cheese.

Skyr
Skyr is a thick fermented dairy product that is traditional
in Iceland. Like Greek yoghurt, it is high in protein
(around 12%) and calcium. Either the strained or direct
set process can be used. Initially a popular product in
Denmark and other Nordic countries, it is now available
worldwide. This market growth is mainly due to the value
proposition of Icelandic cultures, and Skyr’s novel taste
and texture.

Cultured (sour) cream

Cultured cream is produced from pasteurised cream
by inoculating with appropriate cultures and allowing
it to ferment. The fat content is normally reduced to
18% to 23%. Crème fraîche has around 40% fat and is
lightly cultured.

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8.6 8.6.2
Dairy ingredients Milk
Cultured products (yoghurt) can be manufactured from
8.6.1 the milk of any mammal. Although the fat content of
any milk may be adjusted to suit market demands, the
Introduction protein content has the most influence on final product
quality. For most cultured products, fresh or recombined
This section describes the dairy ingredient options
milk is generally enriched (standardised) with milk solids
for yoghurt production (for more information, see
to achieve the target composition required for the
Chapter 2 – Ingredients). Milks frequently require some
product type. Several options are available for protein
protein enrichment or protein standardisation for
enrichment of milk for cultured products. The resulting
cultured product manufacture. The ingredient types
milks will vary in their chemical composition and/or
are described below under the following categories:
physiochemical character, which will also affect the
milk powders, MPCs, WPCs and sodium caseinate. The
final product.
impact each ingredient has will depend on its type and
addition rate, as well as the overall formulation and
processing conditions for the final product. Common 8.6.3
ingredients and typical compositions are outlined below Milk powders
in Table 8.3.
Information in Table 8.4 assumes the ingredients WMP
are used in relatively high amounts, e.g. to provide WMP has 23% to 26% protein and 26% to 28% fat and
> 1% protein. is generally used for full-fat cultured products. It has the
same protein profile as milk (80:20 casein:whey protein).

Table 8.3:
Typical compositions of the common dairy ingredients used in cultured products.

Component Fresh milk SMP WMP Caseinate MPC WPC

Protein (%) 2.8 – 3.5 33.4 25 > 90 56 – 85 34 – 85

Casein:whey 80:20 80:20 80:20 97:3 80:20 0:100

Fat (%) 0.1 – 3.0 0.8 26.8 1.0 2 – 26 5.0

Lactose (%) 4–6 54.1 39.1 < 0.5 6 – 30 5 – 60

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EXPERT TIP:
Low-heat SMP is recommended
for cultured products.
Although medium-heat SMP is the
most commonly available type, low-

Cultured Products
heat SMP is recommended for most
cultured products to help maintain the
viscosity and water holding capacity
in the final product. This is because
the lower amount of denatured whey
proteins in the SMP allows more
casein:whey protein interactions during
the yoghurt milk heat-treatment step,
for greater contribution to the gel
structure.

Table 8.4:
Observed properties of dairy ingredient options for cultured foods (1% top-up basis).

Feature Fresh milk SMP WMP Caseinate MPC WPC fWPC

Flavour Good Good Good Poor Good Typical whey Typical whey
flavour flavour

Stirred Low Low Low High Med-High Low-Med Low

viscosity

Set yoghurt Weak Medium Medium Firm Firm Brittle Weak

texture

Smoothness Good Good Good Poor Good Good Good

Ferment time Slow Slow Slow Med-Fast Med Med-Fast Med-Fast

Shelf life Good Good Good Good Good Caution (for Good
stirred yogurt)

Limitations Variability Flavour and Limited by fat Poor flavour Need to select Formation Will not add
across the fermentation content and sandy appropriate of lumps texture to
seasons time in Flavour and texture when MPC to (aggregation) high-protein
and requires higher-protein fermentation used at high achieve target over shelf life yoghurt
ultrafiltration systems time in higher addition rates texture when used
or evaporation protein at high levels
to increase systems in stirred
protein or drinking
content yoghurts

Skim milk powder (SMP) Fat-filled milk powders (FFMPs)

SMP has 33% to 37% protein and approximately FFMPs, are milk powders where the natural milk fat has
1% fat and, again, the same protein profile as milk been replaced with a vegetable oil. Palm oil and coconut
(80:20 casein:whey protein). SMP is more widely used, oil are frequently used. The protein and fat contents
as the low-fat content provides greater flexibility in of FFMP are usually comparable to standard WMP.
formulation. It can be used alone for low- or zero- FFMP performance in a yoghurt application is similar
fat formulations, or with AMF or cream for full-fat to WMP. The taste will be different as the replacement
formulations. fats and oils will have a different flavour profile from the
original milk fat. FFMPs are often used in countries, or by
SMP is available with different heating specifications
manufacturers, where the cost of WMP ingredients is a
including low heat (LH), medium heat (MH) and high
hurdle to their use.
heat (HH).

197
 Figure 8.3:
Example of lumpiness with a WPC in a 6% protein yoghurt.

EXPERT TIP:
Avoiding lump formation.
To achieve a smooth product
with no lump formulation,
it is recommended that the
whey protein is less than 30%
of the total protein in the
final yoghurt.

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EXPERT TIP:
A useful casein:whey protein ratio
A ratio of no less than 75:25
casein:whey protein in yoghurt milk
will give good gel strength and

Cultured Products
viscosity to the product, and reduce
sandy texture and syneresis (serum
separation) during shelf life.

8.6.4
MPCs
MPCs have become the preferred ingredients for protein
standardisation in many cultured products around
the world. This is due to the numerous benefits they
provide, including good gel strength, viscosity, flavour,
shelf life stability, and versatility to suit the full range of
formulations. Functional MPC ingredients provide more
texture, flavour and processing benefits than standard
MPCs and other ingredient options.

8.6.5
WPCs
Historically, WPCs have been used as ingredients in
yoghurt to provide smooth texture and good water-
holding capacity. However, in stirred cultured products
there is generally a WPC addition-rate limit, due to
lumps forming during the product’s shelf life. The
casein:whey protein ratio in these WPCs is 0:100. The
main benefit of using WPCs is reduced syneresis (serum
separation) during the product’s shelf life.

Functional WPCs (fWPCs)

Functional WPCs can be used at high addition levels in
yoghurt to increase protein content while maintaining a
low viscosity. Increasing the protein content with other
dairy protein ingredients raises the viscosity of the stirred
yoghurt, which can make it difficult to process. Because
fWPCs cause very little viscosity increase, they are
particularly useful in drinking yoghurts and high-protein
yoghurts, or in any cultured product where a lower
viscosity is required.

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8.
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8.6.6 8.7
Sodium caseinate Non-dairy ingredients
Sodium caseinate has traditionally been used to provide
increased protein content and high viscosity in yoghurts. Several common non-dairy ingredients are
The general composition of caseinate is > 90% protein used in the manufacture of cultured products.
and around 1% fat, and it has a casein:whey protein This section briefly describes the frequently
ratio of around 97:3. used ones – starter cultures, and stabilisers.
The yoghurt milk casein enrichment provided by this
ingredient increases the strength and viscosity of the 8.7.1
yoghurt by producing a stronger gel network. Starter cultures
8.6.7 Starter cultures are used in cultured products to convert
lactose to lactic acid, which lowers the pH of the milk.
Ingredient blends This causes the milk to coagulate and form a gel.
In some cases, blending dairy ingredients allows exact Generally, yoghurt is made using the thermophilic (high
product texture and taste selection. Blending standard temperature loving) cultures Streptococcus thermophilus
MPCs, either with fMPCs or with functional and Lactobacillus delbrückii subsp. bulgaricus. The fresh
and standard WPCs, allows customisation of the cheese-type products, such as petit suisse and quark,
product attributes for the desired market. use the mesophilic (moderate temperature loving)
cultures Lactococcus lactis subsp. cremoris and
Lactococcus lactis subsp. lactis. Some other cultured
products, e.g. kefir, use yeasts.

8.7.2
Stabilisers
Non-dairy stabilisers are often added to cultured
products to improve the textural properties and stability.
The non-dairy stabilisers are typically chosen because
they are cheaper than dairy proteins and favoured in
low-protein systems. Addition levels are normally low
and range from 0.1% to 1.5% (w/w) depending on
the type of additive, solids content, fat content, pre-
treatment, heating, homogenisation and the desired
product texture.
Many stabilisers are available for use in cultured dairy
products, each providing slightly different characteristics
to the final product. They can be used alone, in
combination with other stabilisers, or together with
milk proteins, to provide specific functionality. A good

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Cultured Products
stabiliser should be flavourless, odourless, effective at The DE has an important influence on the functional
low pH, easily dispersed and shear resistant. properties of the pectin.
In general, commercially used non-dairy stabilisers are Pectins are used for:
either proteins or polysaccharides (hydrocolloids). Both
• Stabilising properties, as they prevent protein
types increase the viscosity because they are active
aggregation during either acidification or heat
water binders, primarily due to the intra- and inter-
treatment, which in turn prevents phase separation,
molecular bonds formed between the molecules.
syneresis, casein flocculation and sedimentation.
The most widely used stabilisers in yoghurt are gelatin • Gelling/thickening properties, as the pectin chains
(a protein), and starch and pectin (polysaccharides). associate and form a three-dimensional network.
Local legislation and importation regulations covering • In drinking yoghurts, the stabilisers (usually HM
the use of stabilisers can vary widely and must be pectins) serve to hold the gel particles in suspension
consulted before including stabilisers in a formulation. and prevent aggregation and sedimentation.

Gelatin In yoghurts
Gelatin is a protein obtained from hydrolysed collagen. • LM pectins react with calcium to improve yoghurt
It forms a thermo-reversible gel with an elastic texture texture – increase firmness, reduce whey syneresis
that contributes to a smooth, even-textured consistency and enhance stability.
and creamy ‘melt in the mouth’ sensation. • HM pectins improve gel strength in set yoghurts and
viscosity in stirred yoghurts.
Starch
• Typical dose rates are 0.2% to 0.5% (w/w) – too
Starch is a polysaccharide extracted from plants, such as high a dose will disturb fermentation and produce a
corn, potato, tapioca, wheat and rice. coarse structure.
It can be in a native form, or a form modified by
In acidified (fermented) milk drinks
physical or chemical treatments. Each type requires
specific temperature and time treatments to HM pectins will:
achieve maximum functionality. The starch addition
• Protect proteins from denaturation during
rate, overall product formulation and process
pasteurisation (specific to DE 68% to 72%).
conditions for the cultured product will determine the
final functionality also. • Bind with casein micelles at low pH (below the
isoelectric point).
Starches give body to the yoghurt and reduce syneresis
• Prevent sedimentation and flocculation.
and are often used in combination with gelatin.
• Enhance stability.
Pectin
Pectins are linear polysaccharides found in the cell walls
of most plants and fruits, such as citrus.
There are two forms of commercial pectins, each
categorised by the degree of esterification (DE):
• Low methyl ester (LM) pectins with a low DE.
• High methyl ester (HM) pectins with a higher DE.

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References

Cultured Products
1. Codex (2018). Codex Standard for Fermented Milks.
CODEX STAN 243-2003. Codex Alimentarius, FAO/
WHO, Rome, Italy.

203
9.
Cheese Milk
Extension and
Recombined
Cheese
This chapter provides information
about cheese milk extension (CME)
and recombined cheese, particularly
high total solids recombined
cheese (HTSRC).

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9

Cheese Milk Extension and Recombined Cheese

9.
Cheese Milk Extension
and Recombined Cheese

9.1 transition from protein standardisation at the low

end to HTSRC at the extreme is more easily identified
Introduction by the change in processing equipment required to
manufacture the cheese.

9.1.1
CME 9.2
The basic principle of CME is to add reconstituted milk
CME
solids to fresh milk to increase the milk volume used in
traditional or slightly modified cheesemaking processes.
The main purpose of CME is to increase the
This is either done through adding milk solids (protein volume of cheese milk by adding milk solids.
and fat) directly to the milk (low levels of extension) or This is typically driven by the shortage or high
by reconstituting milk solids in water and then blending cost of local milk for cheesemaking.
with fresh milk (medium–high levels of extension). In this
Another main purpose is to increase or standardise the
manual, the term ‘cheese milk extension’ also includes
protein content of the local milk, e.g. from 3.0% to 3.8%,
cheese milk protein standardisation (where only milk
by adding milk solids either directly or in a concentrated
protein is added to the milk). For further information on
form. This is typically done to increase the cheese
milk extension see Chapter 3, section 3.5.
throughput or yield from a given plant or to standardise
production.
9.1.2
Recombined cheese
Recombined cheese is made from recombined
ingredients with no addition of fresh milk. In this manual,
recombined cheese will also include cheese made from
non-dairy components such as vegetable oil.
Recombined cheese may be made in the following ways:
• The ingredients are recombined to the same TS level
as the usual cheese milk and the cheese is made in
the traditional way with only minor modifications.
• The ingredients are recombined to the TS level of the
final cheese and the cheese is made with no water/
whey separation prior to packing.
Cheese made in the second way is often referred to
as high total solids recombined cheese (HTSRC) and
requires a more modified cheesemaking process. More
information about HTSRC is provided in section 9.5.
There is a large variety in the possible ratio of fresh
milk to reconstituted ingredients (see Figure 9.1). The

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Cheese Milk Extension and Recombined Cheese

Figure 9.1:
Increasing addition of milk solids requires modifications to the cheesemaking process.

Increasing amounts of milk solids added

Increasing yield per litre of local milk

Cheese Milk Extension

(CME) Increasing Solids

High Total Solids

Cheesemaking Protein Cheese Milk Extension
Recombined Cheese
from Fresh Milk Standardisation (CME) Increasing Volume
(HTSRC)

Recombined Cheese
(Low-Solids)

Traditional cheesemaking Non-traditional process

Traditional cheesemaking
with modifications No liquid/whey separation

9.2.1 Reduced capital cost: Purchasing equipment to

standardise milk using protein products may be more
Potential benefits cost effective than equipment for separation and
The benefits of CME or recombined milk for cream removal.
cheesemaking can be specific to an individual Greater flexibility: By removing variations in local milk
manufacturer or country. Here are some composition, CME gives manufacturers the option
common examples. to supply customers with different cheese varieties
Reduced protein costs: Imported milk protein may be throughout the year.
cheaper than that sourced from local milk, which can Less dependence on local supply: By minimising the
result in increased margins. impact of seasonal or year-round reductions in local
Better process control: CME may be used to standardise milk supply, CME can allow cheese manufacturers to
the protein content of the milk throughout the day and make their full product range or create new additions
across the season to support process optimisation. at any time.

Improved product quality: CME may be used to increase Reduced whey production: For some cheeses, using
the protein content of the milk to improve product CME will reduce the amount of whey produced, which
quality or to manufacture a product to specification. For may benefit manufacturers in areas with difficult or
example, fresh milk with only 3.2% protein does not give expensive whey disposal.
good gel-forming properties and CME may be used to
increase milk protein to a level that does.

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Cheese Milk Extension
and Recombined Cheese

9.2.2 The extender is directly added to the cheese

CME options milk before pasteurisation.
For this method the extender must have good
For CME the milk solids may be included into the fresh
wettability, dispersibility and solubility. Typically, these
milk in several ways.
properties must exist at low temperatures as it may
not be feasible or desirable to heat the cheese milk to
recombining temperatures. High-shear mixing should
be avoided also as this will damage fat globules in the
cheese milk. In this case, milk powders or milk powder
concentrates (MPCs) are preferred. The preferred fat
addition would be cream or whole milk powder (WMP),
as in this scenario a pure fat would not be stabilised and
could easily separate.

Figure 9.2:
CME process where the extender
is directly added to the cheese milk
before pasteurisation.

Milk Fat Addition

Fat
Cheese Milk More Cheese
Protein

Whey

Milk Protein Addition

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Cheese Milk Extension and Recombined Cheese

The extender is reconstituted in a portion
of the skim milk.
This is then added to the remaining fresh milk before
pasteurisation and cheesemaking. With this method,
it may be possible to heat the portion of skim milk to
desired recombining temperatures, and high-shear
mixing may be used if required. This would allow the
use of a wider range of fat sources.

Figure 9.3:
CME process where the extender
is reconstituted in a portion of the
skim milk.

Milk Protein Addition

Milk Fat Addition

Portion of Fresh
Milk Stream

Milk Supply More Cheese Milk

Fresh Milk

Whey

More Cheese

209
9.
Cheese Milk Extension
and Recombined Cheese

The extender is reconstituted in This is perhaps the most common method. It allows
water then added to the cheese milk reconstitution at an optimum recombining temperature
before pasteurisation. and high-shear mixing if necessary. The extenders are
recombined to 10% to 30% TS. The exact percentage will
depend on the ingredient’s limitations, the equipment
used and the cheesemaking requirements.

Figure 9.4:
CME process where the extender is
reconstituted in water then added to
the cheese milk before pasteurisation.

Milk Protein Addition

Milk Fat Addition

Water

More Cheese Milk

Fresh Milk

Recombined cheese using a

traditional process.
As previously outlined, ingredients may be recombined
in water to the same TS level as normal standardised
milk for cheesemaking. The cheese is made in the usual
way with minor modifications. The same approach to
ingredient selection and cheesemaking process changes
is taken as for CME. Therefore, the general guideline is a
maximum of 4% total protein in the milk to avoid major
process amendments.
Information about non-traditional recombined cheese
(HTSRC) is given in section 9.5.

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EXPERT TIP:
Protein should not be > 4%.
As a general guideline, care should
be taken when standardising
or extending cheese milk above

Cheese Milk Extension and Recombined Cheese

4% total protein. Over this
level, significant changes to the
cheesemaking process or equipment
may be needed.

9.3 9.3.2
Recombining Powder dispersion and hydration
Hydration is when the dispersed powder is held in
Detailed information has been provided in water to solubilise the milk components before further
Chapter 3 on processes used in recombining, processing. Hydration also allows time for entrained air
hydrating and further treatment of or foam to separate out of the milk. Hydration times
recombined milks. This section provides are very important. Continuous stirring or pumping is
valuable information for recombining in the essential; otherwise product settles.
context of preparing a cheese milk for a When reconstituting standard milk powders – skimmed
natural cheese process. milk powder (SMP) whole milk powder (WMP) or
MPC56, the basic colloidal structure of the protein
9.3.1 becomes established relatively easily at temperatures
as low as 20°C. As the recombining process itself often
Water for recombining takes longer than 20 min, there is seldom a need to make
special provision for a hydration period.
If water, rather than local milk, is used to reconstitute
ingredients in a CME or recombined cheese process, it We recommend higher reconstitution temperatures for
must have: higher-protein MPC ingredients. For example, MPC70
requires a minimum of 20 min hydration at 40°C to 60°C,
• Good microbiological quality.
and MPC85 needs a minimum of 30 min hydration at
• No chemical or inhibitory substances that
40°C to 60°C.
may be hazardous to health or affect the
cheesemaking process. Typical hydration times and temperatures for different
MPCs are shown in Chapter 8, Table 8.3. Problems can
• No disagreeable tastes and smell.
occur with cold water recombining; dissolving may be
In general, water should comply with the water incomplete and this makes homogenisation difficult.
standards set by the World Health Organization. Water A water temperature of approximately 50°C, if possible,
quality for ingredients is also discussed in Chapter 2. improves dissolution.
To prevent off-flavours in the recombined cheese, the
water’s chlorine content should result in no more than 9.3.3
25 mg of chlorine per litre of reconstituted milk (Gilles &
Deaeration
Lawrence, 1981).
Using hard water (i.e. > 500 mg/L as calcium carbonate Air in the product can reduce homogenisation efficiency
– CaCO3) results in protein instability in reconstituted and may increase heat exchanger fouling. Deaeration is
milk and can lead to yield losses in the subsequent recommended for HTSRC systems as air can be trapped
cheesemaking operation (Sargent et al., 1959). The in the body of the cheese as it sets. Air or foam can be
presence of carbonates and bicarbonates in water removed more quickly and efficiently by passing the milk
can result in a prolonged rennet coagulation time and through a deaeration device.
reduces curd tension during cheese manufacture (Gilles
& Lawrence, 1982).

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9.
Cheese Milk Extension
and Recombined Cheese

9.3.4 that may form after the primary homogenisation of

high-fat milks.
Fat addition
For flavour-sensitive cheese products, it is better to
Effects
add the fat as late as possible during the recombining Viscoelastic (both elastic and viscous) properties are
process. Holding the fat at warm temperatures and very important in homogenisation. Consistent handling
subjecting it to high shear causes oxidation and off times and temperatures before homogenisation are
flavours. However, fat may be added before the protein very important.
to reduce cheese milk foaming.
Homogenisation increases the fat surface area and the
It is common to prepare a recombined cream at 30% system becomes more hydrophobic, or water repelling.
fat, which can be used to 'standardise' the recombined This affects flavour.
milk. This may be achieved by dissolving a portion of
Homogenisation is not just about recombining cream
the non-fat milk solids – either or both of SMP and
and skim milk; it also affects the final texture of
buttermilk powder (BMP) – and hydrating at 55°C to
the cheese.
60°C, and then adding melted fat – anhydrous milk fat
(AMF), unsalted butter or vegetable oil ­– followed by • For short structures (e.g. feta or crumbly cheeses),
pasteurisation and homogenisation before cooling and fat can be associated with the gel. However, for
adding to the milk or milk protein solution. It is important plasticity (sliceable, flexible cheeses), fat must not
to prevent too much separation of this two-phase be so closely associated with the gel.
system prior to homogenisation. • To minimise fat associating with the protein gel
system, the cream could be made up separately,
9.3.5 e.g. prepare the cream (recombine, pasteurise,
Homogenisation homogenise, cool) and add it to the milk and/or
recombined protein base in the cheese vat.
Homogenisation is used to disperse fat globules in the
recombined milk or cream. 9.3.6
Temperature and pressure
Pasteurisation
A homogenisation temperature of 55°C to 60°C is The recombined milk must be pasteurised (72°C for
usually recommended. Different brands of homogeniser 15 s), or at least thermised (65°C for 15 s), as the
create different degrees of homogenisation for the same hygiene of the recombining equipment and process
level of pressure. Homogenisation pressure affects the cannot be guaranteed. It is particularly important
functional, textural and sensory properties of the final that pasteurisation or thermisation takes place if the
product. The protein-to-fat ratio affects the level of recombined milk is to be held for more than 4 h at ≤ 4°C
homogenisation required. before further processing.
To ensure product integrity in terms of microbiology,
Single- or two-stage the pasteurisation step must follow homogenisation;
Single- or two-stage homogenisation may be used for otherwise the milk may become recontaminated in
unconcentrated milks, but two-stage homogenisation the homogeniser. However, pasteurisation heating
is necessary for concentrated milks. Secondary may affect the emulsion and if good emulsion stability
homogenisation breaks up any fat-globule clusters is essential, pasteurisation may be carried out prior
to homogenisation.

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EXPERT TIP 1: EXPERT TIP 2:
Remove entrained air before fat High-shear mixing is an alternative
addition and homogenisation. to homogenisation.
It is better to remove entrained air In Latin America, high-shear mixing is
before fat addition (if it is in-line) and sometimes used as an alternative to

Cheese Milk Extension and Recombined Cheese

prior to homogenisation. Otherwise the homogenisation. This has been found
homogeniser reduces the air particle to give good dispersion of the fat but
size and it is harder to deaerate at a more added emulsifier is needed to
later stage in the process. achieve favourable results.

9.4
Adjustments to traditional
cheesemaking process
This section highlights some important
processing considerations when making
cheese using CME. These guidelines apply to
'fresh'-style cheeses (soft, unripened). For
harder, ripened cheeses, CME may become
unsuitable as the level of extension increases.

9.4.1
Use of starter culture
For CME and recombined cheese the higher protein level
in the cheese milk may cause an increased buffering
capacity and acid development may be slowed. This
can be mitigated by adding more starter. If the cheese
is acidified directly (by adding acid or glucono-delta-
lactose), the rate of pH drop may be affected as well,
and the amount of added acid may need to be adjusted.

9.4.2
Factors impacting rennet coagulation
Adding calcium chloride (CaCl2 )to the milk increases
the colloidal calcium phosphate concentration, raises
the coagulation rate and increases the firmness of the
gel. Codex (Codex, 2017) allows up to 0.02% CaCl2 to
be added to fresh milk. Addition of CaCl2 is a common
practice in CME and recombined cheese manufacture,
as many of the ingredients used have a lower ratio of
calcium to protein than fresh milk. Careful consideration
must be made of the desired properties of the end
product, as too much calcium may affect maturation,
melting properties, etc.
The amount of CaCl2 needed differs for each milk
protein, and depends on the other components used in
the recombined system, such as milk, water or cream.

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Cheese Milk Extension
and Recombined Cheese

The necessary amount of CaCl2 can be determined whey. Cutting of the curd may need to be quicker also,
experimentally in a chosen system. to avoid a brittle curd from forming.
In principle, the relative amount of CaCl2needed
increases as follows: 9.4.3
Fresh milk → SMP → BMP → MPC56 → MPC70 → Cutting the curd
MPC4424 → Calcium caseinate → Sodium caseinate
→ Lactic casein For extended and recombined cheese milks with a higher
protein content, the cutting of the curd may need to
CaCl2 should be added slowly to solutions containing
be carried out more quickly than normally practised, to
casein, caseinate or total milk protein (TMP) to avoid
prevent a brittle curd forming.
precipitation. A 10% solution is generally recommended
in all cases. Extended and recombined cheese milks
may set at a different rate to normal cheese milk. It is, 9.4.4
however, important to keep the set time of the curd Stirring/Cooking
unchanged as the rate of cheese milk coagulation is
crucial to the quality of the final cheese. Altering the For extended and recombined cheese milks, the rate of
rennet level is one way of controlling this. Generally, curd syneresis and texture development during cooking
a higher protein level in the cheese milk will result in and stirring is another critical step. In general, a cheese
a shorter setting time; therefore, less rennet should with a higher protein content will synerese faster than
be added. usual before the required pH is reached. This results in a
tougher curd. Cooking at a lower temperature will help.
If no adjustment is made, a brittle curd may result; this
will synerese further, and more fines will be lost in the

Table 9.1:
General total solids guidelines for some ingredients in HTSRC.

SMP/WMP/BMP 45% total solids for pump and funnel, depending on design
45% total solids for tri-blender
50%–55% total solids for Cowles dissolver

MPC56 3%–5% lower total solids than for SMP

MPC70 Approximately 10% lower total solids than for SMP

Caseinates 20% maximum total solids in Cowles dissolver or similar equipment (caseinates
perform better close to 20% total solids than at lower total solids)

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EXPERT TIP 1: EXPERT TIP 2:
Higher pasteurisation temperatures HTSRC compared to processed cheese
weaken the properties of hard and Although HTSRC and processed
semi-hard cheeses. cheese often use the same or similar
The maximum treatment ingredients, their different processing

Cheese Milk Extension and Recombined Cheese

recommended for hard or semi-hard methods create two unique products.
cheeses is the standard 72°C for Recombined natural cheese uses
15 s. Anything higher than this rennet and/or acid to set cheese,
affects syneresis, gelation, setting whereas processed cheese applies
time and final texture. Higher heat, shear and emulsifying salts to
pasteurisation temperatures may be form a homogeneous product.
used for soft cheeses. Pasteurisation
treatment is a legal minimum milk
safety control requirement.

9.5 9.5.2
High total solids recombined Typical uses
cheese (HTSRC) HTSRC is more suitable for fresh and softer cheese
varieties. These product types cover a variety of high-
moisture, unripened cheese curds. They typically have a
9.5.1 short shelf life and must be kept refrigerated. They vary
What is HTSRC with the region of origin and whichever term is used
– quark in central and Eastern Europe, fresh cheese in
Recombined cheeses are made from recombined Western Europe and queso fresco in the Latin American
ingredients without adding fresh milk. The ingredients regions (all are generic terms for products covering a
include a source of non-fat milk solids, milk fat and water broad range of fat contents).
to achieve the physio-chemical, nutritional and sensory
The HTSRC process is not usually suitable for hard and
characteristics of a natural fresh cheese. Formulations
semi-hard cheese types because the texture and flavour
may also include a range of other dairy and
of these cheeses is typically created through the chemistry
non-dairy ingredients.
and microbiology of the traditional cheesemaking process.
For HTSRC, the ingredients are recombined to a TS Numerous studies have attempted to develop hard and
level of the final cheese, e.g. 30%–40% TS, rather than semi-hard cheeses (such as cheddar and gouda) using
concentrated by removing liquid high solids processes without a draining step; however,
(whey/water). none have been promising enough to lead to commercially
successful products.
The cheese milk TS level that can be used for a HTSRC
system is limited by viscosity and to some extent
the level of aeration. This can vary depending on the 9.5.3
equipment, so it is difficult to give exact limits. A TS limit Potential benefits
could be determined experimentally, or with the advice
of equipment manufacturers. Refer to Table 9.1 for TS HTSRC may be attractive for the following reasons:
guidelines for dairy ingredients in HTSRC.
• Situations where there is an established cheese
market and local food legislation permits
recombined cheese manufacture but:
• The local milk supply does not meet demand
for all or part of the season and the extension
of local milk (CME) will not meet the shortfall.
• The quality of local milk is insufficient or
too inconsistent to make the required
cheese products.
• Imported ingredients are cheaper than local milk.
• Lower capital cost because equipment set-up costs
are likely to be cheaper and simpler than recombined
cheese manufacture.
• Reduced potable water requirements.

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Cheese Milk Extension
and Recombined Cheese

• Reduced or eliminated whey production.

• A simpler cheesemaking process with less labour
and skill required.
• Less rennet is needed.
Common types of cheese made using HTSRC include
feta and other salty white cheeses, cream cheese,
and panela.
MPCs are generally the most suitable ingredients for
HTSRC, due to their ability to react to rennet and form
a gel after filling and because they incorporate whey
protein into the final product. The correct selection
of ingredients depends on clear understanding of the
characteristics of each cheese variety, as well as the
functionality of each ingredient and its interaction with
the rest of the system. This often requires an extensive
amount of research and development.
See Figure 9.2, which details a generic HTSRC process.

9.6
Ingredient selection
Selecting the right ingredient can depend on
many factors. It can depend on ingredient
performance in an application and a wide
range of market-specific factors.
The most important market-related factors are:
• What is permitted for use in CME or for
recombined cheese.
• What local tariffs and import restrictions allow,
and the price at which they are economical to
the cheesemaker.
Table 9.2 summarises the advantages and
considerations for a variety of common ingredients
used in CME or recombined cheese manufacturing.

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EXPERT TIP 1: EXPERT TIP 2:
Popular ingredients may no longer Choose ingredients based on
be the best available. their compatibility with CME or
In many cases, ingredients were recombined cheese.
initially used in applications because In general, from a purely technical

Cheese Milk Extension and Recombined Cheese

that is what was available at the point of view, ingredients for any
time and they continue to be used cheese system should be chosen for
out of habit. Therefore, just because their compatibility with that system.
an ingredient is being used in an Consequently, the constituents of the
application, and may be widely ingredient should be in the right form
used, it does not mean it is the best for cheesemaking. On this basis, the
ingredient for that application. preferred ingredients for either CME
or recombined cheese in descending
order of compatibility are: milk powder,
MPCs, caseinates, TMPs and casein.

Figure 9.5:
The HTSRC process.

Deaeration is recommended:
• Vacuum on recombining tank
or
• Deaeration vessel in line
before homogeniser
Hydration

Powder Skim Milk

Homogenisation Pasteurisation
Dispersion Fat Addition

Funnel Pump Pump Homogeniser PHE

Preparation
Tank

Dosing Funnel Pump

Packaging Pump Batch Tank

Fermentation
and Flavours

Rennet Addition
and/or starter cultures or
other ingredients

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 Table 9.2:
Advantages and considerations for a range of common ingredients used in CME or recombined cheeses.

Ingredient Cheesemaking utility Ingredient considerations Typical use

Skim milk powder • Same casein:whey ratio as • Missing phospholipid CME or fully recombined (low
(SMP) fresh milk. component. solids) cheese (using traditional
• Flexibility to produce a range • Additional processing required process)
of formulations. if fat needs to be included in • Low-heat SMP preferable for
• Long shelf life. the recombined milk. medium-hard cheeses.
• Easy to handle and recombine. • Only small amount of • Low-medium heat suitable
• Good source of lactose. rennetable solids approx. 30% for soft cheeses.
• Clean flavour. • Can give powdery curd at high
extension levels. 30% – 200% protein extension.
• Excessive lactose can cause
gummy texture in CME cheese.
• High lactose limits use
in HTSRC.
Whole milk powder • Same casein:whey ratio as • Less formulation flexibility As for SMP.
(WMP) fresh milk. (cannot adjust protein and fat
• Single ingredient to levels independently).
recombine; no requirement • More rigid and less pliable
for fat processing. cheese texture because
• Composition the same as fat globules have been
fresh milk. homogenised and casein
dispersion is different from
fresh milk.
• Excessive lactose can cause
gummy texture in CME cheese.
• High lactose limits use in
HTSRC.
Butter milk powder • BMP can gives the cheese a • High heat treatment of Provides phospholipid content
(BMP) smoother texture, reduced BMP limits its use to small when used at low levels with
grittiness and increased percentages, especially in other protein extenders. This
moisture. hard cheese types. Can affect can improve flavour, texture
• Typically low cost. gel formation and reduce and recombining properties.
syneresis.
• Microbial quality may not 30% – 90% protein extension.
be reliable from some
manufacturers.
• Excessive lactose can cause
gummy texture in CME cheese.
• High lactose limits use in
HTSRC.
Milk protein • Rennets well. • May be less cost effective in CME: Fresh or firmer
concentrates (MPC) • Clean/milky flavour. hard cheese applications. (ripened) cheeses.
• Casein is in the natural
Ripened cheeses:
micellar form.
Up to 30% protein extension.
• Same casein:whey ratio as
fresh milk. Fresh cheeses:
• Long storage life. Up to 300% protein extension.
• Less lactose compared
to SMP. HTSRC: Fresh cheeses.
• Improved whey stream
quality with a greater
protein/lactose ratio.
• Protein levels in cheese-
making can be reached with
smaller amounts of extender.
• Relatively low lactose
content allows HTSRC.

Specific MPCs Specific MPCs Specific MPCs

• MPC56: Easiest hydration • MPC56: High lactose content. • MPC56: High CME level +
and recombining. HTSRC.
• MPC70: Care needed to
• MPC70: Often the most minimise aeration. • MPC70: High CME level +
economical protein source. HTSRC.
• MPC85: Slower/longer
• MPC85: Smaller amount of hydration. Can have difficulties • MPC85: Standardisation (low
powder to be handled. recombining, or with aeration. CME levels).
• 'Functional' MPCs: Some can • 'Functional' MPCs:
be more easily hydrated (see Low-medium CME levels.
Chapter 8, Table 8.3).

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Table 9.2:
Advantages and considerations for a range of common ingredients used in CME or recombined cheeses.

Ingredient Cheesemaking utility Ingredient considerations Typical use

Cheese Milk Extension and Recombined Cheese

Calcium caseinate • Gives a very filamentous • High levels of calcium CME may be useful in
structure, i.e. a long gel that chloride are required to aid stretched curd products.
gives good stretch. the rennet reaction. This may
• Reacts with rennet but only lead to poor flavour at high
has half the calcium-to- extension levels.
protein ratio as in the normal • Note that the structure is
casein micelle; therefore, very fragile at cutting and
calcium chloride would may result in large losses if not
be needed. handled carefully.
• Performance can be variable
depending on caseinate
source. Proper handling and
hydration are important.
Sodium caseinate Not recommended for use • Poor flavour. Low-medium CME levels in
in CME or HTSRC, but is • Increases the viscosity of the fresh cheeses.
sometimes economically cheese milk. Acid-precipitated cheeses.
favourable in some markets. • Requires high-shear
recombining equipment.
• Presence in milk interferes
with the rennet reaction. Very
high levels of calcium chloride
are required to aid the rennet
reaction, which may cause
bitter flavour.

Acid casein • Not recommended. • Poor flavour as usage Low-medium CME levels in
• Requires conversion to level increases. fresh cheeses.
a soluble form (typically • Converting to sodium Acid-precipitated cheeses.
to sodium caseinate by caseinate risks adding
reacting with NaOH). soapy flavours.
This requires proper • Presence (of converted
process control. caseinate) in milk interferes
with the rennet reaction. Very
high levels of calcium chloride
are required to aid renneting.

Anhydrous milk fat • Depending on the desired • Needs non-fat milk solids and/
(AMF) outcome, different milk fat or emulsifiers present to help
products can be used to form a stable emulsion.
affect the type of emulsion
that is formed; this in turn
will affect the flavour,
mouthfeel, appearance,
consistency and texture of
the cheese.
• Fresh frozen milk fat for
recombining (FFMR) also
provides an option of AMF
in a smaller, more convenient
format.
• Milk fat can be blended with
vegetable oils.

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References

Cheese Milk Extension and Recombined Cheese

1. Gilles, J. & Lawrence, R. C. (1981). The manufacture
of cheese and other fermented products from
recombined milk. New Zealand Journal of Dairy
Science Technology, 16, 1–12.
2. Gilles, J. & Lawrence, R. C. (1982). The manufacture
of cheese and other fermented products from
recombined milk. Bulletin of the International Dairy
Federation No. 142, 111–117, International Dairy
Federation, Brussels, Belgium.
3. Sargent, J. S. E., Higgs, D. A., & Irvine, D. M. (1959).
Effect of hard water on the stability of skimmed milk
powder. Journal of Dairy Science, 42, 1800–1805.

221
10.
Nutrition
This chapter provides high-level information
on the nutritional components of liquid milk
and common recombined milk ingredients. It
also includes a brief discussion on low-level
nutrients, adding less-healthy ingredients,
how processing affects some nutrient
levels, and the role of dairy-based
products in the global food system.

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Nutrition
10
10.
Nutrition

10.1 Here is a brief summary of each nutrient’s

role in the human body:
Nutritional value of liquid milk
Protein
Milk is recognised as an important and Protein is used in the body to provide structure to
nutritious food for people worldwide. Well almost every type of tissue, such as muscles and bones,
known for its calcium, high-quality protein, and to enzymes, immune cells and neurotransmitters
vitamin B2 and vitamin B12 content, milk is (Fukagawa & Yu, 2009).
also a source of the minerals potassium and Milk protein is one of the highest-quality proteins
phosphorus, and the vitamins A, niacin, biotin available in the diet, due to its high concentration of
and pantothenic acid (New Zealand Food indispensable amino acids. As a general rule, protein from
Composition Database, 2019). animal sources is of higher quality than protein from
plant-based sources (see Figure 10.1). The digestible
indispensable amino acid score (DIAAS) is used to rank
protein sources in terms of quality, with scores > 1
indicating a ʼhigh qualityʼ or ʼcompleteʼ protein.

Figure 10.1:
The DIAAS values for a range of dairy and non-dairy protein sources (Burd et al., 2019).

Protein Quality (DIAAS)

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0
Barley
Rye
Soy Protein
Pork

Rice

Kidney Beans
Chicken
WPI

Oats
Casein
WMP
MPC

Beef

Wheat
Pea Protein

Peanut
WPC
Egg

Sorghum

Ingredient abbreviations: MPC - milk protein concentrate, WMP - whole milk powder, WPC - whey protein concentrate.

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Fat three micronutrient priorities (FAO/WHO, 2019). It is
Fat is a dense source of energy for the body, carries fat-soluble and is found in the fat fraction of milk.
fat-soluble vitamins and is the major component of
cell membranes. In recent years the fat in milk has Vitamin B2 (riboflavin)
been shown to be healthier than previously assumed, Riboflavin is involved in energy metabolism and has a
with studies demonstrating that it has either neutral central role in the body’s natural antioxidant systems
or slightly positive effects on cardiovascular health (Bender, 2009b). In most diets, milk provides 25% or
(Alvarez-Bueno, 2019). While widely regarded to be more of the total riboflavin intake.
a saturated fat, almost one third of the fat in milk is
actually mono- or polyunsaturated (New Zealand Food Vitamin B3 (niacin)
Composition Database, 2019). Niacin is heavily involved in the energy-producing
pathways of the body (Bender, 2009c). While milk
Carbohydrate has very little free-form niacin, it does have ample
Carbohydrates are used in the body mainly as a readily amounts of the amino acid tryptophan, which can be
available source of energy. The carbohydrates in milk converted into niacin by intestinal bacteria. A glass
consist of the disaccharide lactose. Lactose is made up of milk can provide the equivalent of 13% of the
of one glucose and one galactose unit bound together. daily niacin requirement, in the form of tryptophan
(FAO/WHO, 2019).
Calcium
Vitamin B5 (pantothenic acid)
Calcium is important for the development and
maintenance of healthy bone and muscle. It also has key Like other B vitamins, panthothenic acid has a central
roles in nerve transmission and muscular contraction role in energy metabolism (Bender, 2009d). It is widely
(Strain & Cashman, 2009a). Milk is a good source of distributed in foods and its name is derived from the
calcium and it makes up a large proportion of the world’s Greek word pantos which means `from everywhere´. For
dietary supply of this essential mineral. this reason pantothenic acid deficiency in humans is not
apparent, except in intentional depletion studies.
Potassium
Vitamin B7 (biotin)
Potassium is a mineral and electrolyte that is critical for
nerve transmission, muscle function and water balance Biotin has a role in energy production and glucose
in the body (Strain & Cashman, 2009b). metabolism. It is widely distributed in foods and
deficiency in humans is essentially unknown
Phosphorus (Bender, 2009e).
Phosphorus is widely distributed in food and the human
Vitamin B12 (cobalamin)
body. It is a component of bones and teeth and is
essential for the transfer and storage of energy within Vitamin B12 is involved in energy metabolism and is
the body (Strain & Cashman, 2009c). important for neurological function and blood cell
formation (Bender, 2009f). Vitamin B12 is only found in
Vitamin A foods of animal origin, making dairy an important source
Vitamin A has an important role in vision and gene for vegetarians with one glass of milk providing up to
expression, helping to regulate growth and development 30% of the recommended daily intake (RDI) of vitamin
(Bender, 2009a). Deficiency is a major public health issue B12 (New Zealand Food Composition Database, 2019;
in many areas of the world and is one of the WHO’s top FAO/WHO, 2019).

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10.2 Influences on micronutrient content

Nutritional composition The micronutrient (vitamins and mineral) content of a
dairy ingredient largely depends on its macronutrient
of common recombining (protein, fat and carbohydrate) composition and the type
ingredients of processing the ingredient has undergone.
Many micronutrients are associated with the protein
From a nutritional point of view, fresh liquid fraction of milk, so higher-protein products generally have
milk has a more predictable nutrient profile higher levels of micronutrients. One notable exception is
than products created by recombining dairy vitamin A. As a fat-soluble vitamin, its level will typically
ingredients. This is due to the different rise with increasing fat levels. As a result, there is very
little vitamin A in low-fat ingredients, such as skim milk
nutrient profiles of ingredients that may be
powder (SMP), milk protein concentrate (MPC), and
used in recombined products.
calcium caseinate, and higher amounts in fat-containing
Table 10.1 shows a representative sample of common ingredients such as whole milk powder (WMP), and
ingredients used in recombined products. The values are very high levels in concentrated fat ingredients, such as
indicative only and some ingredients have more than anhydrous milk fat (AMF).
one variation.

10.3
Minor nutrients present in milk
There are other nutrients in milk than those
discussed above. Cows have evolved so that
milk can be the sole source of nutrition for
calves, so it must contain every nutrient they
need in early life.
While these other nutrients are not present in fresh milk
at levels relevant to the human diet (≥ 10% of the RDI per
serve), they can reach relevant levels in some concentrated
dairy products. One notable example is hard cheese
where the mineral zinc is concentrated up to a level that
the cheese can be considered a ‘source’. Definition of
source depends on the local regulations, e.g. ≥ 10% of
RDI. Conversely, the processing required to create these
products can cause other nutrients to be lost. In the case of
cheese, potassium is lost to the whey component.
For more information on low-level nutrients in recombining
ingredients, consult with your ingredient supplier.

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Table 10.1:
Indicative nutrient composition of typical ingredients used in recombined milk products.

Niacin
Calcium Protein Vitamin B2 Vitamin B12 Potassium Phosphorus Vitamin A equivalents Biotin Vitamin B5

mg/100g g/100g mg/100g mμ/100g mg/100g mg/100g mμ/100g mg/100g mμ/100g mg/100g

WMP 830 24.5 2.0 2.6 1,110 710 270 7 23 4.1

FWMC 436 13.3 1.3 1.4 644 339 100 4 N/A N/A

BMP 970 31.0 2.8 2.8 1,500 900 56 9 34 4.4

Whey
460 15.1 3.9 1.0 2,600 590 <3 7 N/A 2.5
powder

WPC80 400 80.3 0.2 9.0 510 310 26 28 N/A 0.4

Calcium
1,400 92.6 0.2 2.0 4 770 <6 20 N/A 0.5
caseinate

MPC 2,160 81.1 1.4 8.0 280 1,300 < 25 19 N/A 0.6

SMP 1,200 33.4 2.7 3.6 1,600 1,000 5 10 31 5

AMF <1 < 0.01 – – <1 N/A 1,000 – – –

Cream
570 15.6 1.2 2.3 700 450 400 5 17 2.4
powder

Ingredient abbreviations: WMP - whole milk powder, FWMC - frozen whole milk concentrate, BMP - buttermilk powder, WPC - whey protein
concentrate, MPC - milk protein concentrate, SMP - skim milk powder, AMF - anhydrous milk fat.

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10.4 More intense processing, in terms of the risk

conditions outlined above, are likely to result in higher
Adding nutrients associated nutritional loss. By adopting best practices, the risk of

with negative health outcomes product rework is reduced, resulting in less exposure
to unfavourable environments and therefore less
nutrient loss.
Processing dairy ingredients into different
formats sometimes requires the addition More information on nutrient losses can be found in
of non-dairy ingredients that can affect the Chapter 3, section 3.4.13 – Nutritional stability as part of
'truth in labelling'.
final product’s nutritional profile.
These ingredients, such as salts and sugars, may be
added to enhance functional properties, increase shelf 10.6
life and food safety or improve the sensory profile of the
final product. However, as overconsumption of these
Nutrient supply in the global
nutrients is associated with negative health outcomes, food system
their addition should be minimised, without risking the
The health and wellbeing of people worldwide is greatly
safety or functionality of the food.
determined by food supply. A 2019 joint report from the
FAO and WHO noted that the leading risk factors for
10.5 non-communicable diseases (NCD) included low milk

Processes that can affect intake and, specifically, low calcium intakes. In the report,
the FAO notes that high intakes of sugar-sweetened
nutrient content beverages and sodium are also risk factors for NCD
(FAO/WHO, 2019). This indicates why it is preferable
Nutrients may be affected by processing to retain nutrients in milk as much as possible during
conditions, ingredients and storage processing and to minimise the use of added sugar and
sodium in dairy-based products.
conditions. These include, but are not
limited to, heat, acids, alkalis, reducing Nutrient loss vs food availability gains
agents, oxidising agents, humidity and
Efforts to minimise nutritional loss from dairy products
light. Nutritionally, minerals are generally
should be balanced against processing dairy into shelf-
unaffected, and proteins suffer minimal stable formats that allow greater nutrient distribution
effects (small losses of the amino acid lysine to populations that otherwise would not have access to
from Maillard reactions). Vitamins, however, them. Processing may increase access to populations
may be affected, sometimes losing their that lack a chilled supply chain or do not have the ability
biological function (Cifelli, 2010; Fong, 2001). to store unprocessed product without spoilage.
Water-soluble vitamins that are not bound
within the protein matrix are at most risk,
while fat-soluble vitamins, such as vitamin A,
may be protected by the fat matrix.

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Nutrition
Focusing on population-specific Exploring the different ways food is used
nutritional needs Cultural and social considerations are important also, as
When deciding what product to create or what different communities may use foods and ingredients in
processing techniques to use, consideration should be different ways. For example, even though a processed
given to the nutritional needs of the population. For food or ingredient may have suffered unavoidable
example, creating acidic milk drinks and yoghurts by nutrient losses, its availability and inclusion in dishes to
adding cultures alters the pH of the dairy matrix. This enhance taste or cultural acceptance may encourage
would be expected to have some impact on acid-labile the consumption of other foods that supply other
nutrients. However, if digestive health is important to the essential nutrients.
target population (and the cultures used have probiotic
activity and are not inactivated through heat treatment),
the nutritional benefits of the cultures may offset the
small losses expected in pH-sensitive nutrients.

229
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