Unit – 2

Condensed Milk:
Definition-:
Condensed Milk are the products obtained by evaporating part of the
water of whole milk or fully or partly skimmed milk with or without
addition of sugar.
The term ‘condensed’ milk is commonly used when referring to ‘full-
cream sweetened condensed milk’.
The term ‘evaporated milk’ is commonly used when referring to ‘full
cream unsweetened condensed skim milk’.
Skimmed milk products are known as ‘sweetened condensed skim milk’
and ‘unsweetened condensed skim milk’ respectively.
The ratio of concentration of milk solids is about 1:2:5 for full cream
products and 1:3 for sweetened condensed skim milk.
Specifications of various types of condensed milks:
1. Unsweetened condensed milk (evaporated milk) – It’s a product
obtained from cow or buffalo milk or a combination of both, from
standardized milk, by partial removal or water.
It may contain some added nutrients.
2. Sweetened Condensed Milk - It’s a product obtained from cow or
buffalo skim milk or a combination of both, from standardized
milk, by partial removal or water and after addition of cane sugar.
It may also contain some added nutrients but, such additions
need not to be declared on the label.
 3. Sweetened Condensed Skim milk - It’s a product obtained from
cow or buffalo skimmed milk or a combination of both, by partial
removal or water and after addition of cane sugar.
It may also contain some added nutrients exceeding 0.3% by
weight of finished product but, such additions need not to be
declared on the label.
Methods of Manufacture-:

Manufacturing of condensed milk involves 8 different steps which are

explained below:-
I. Receiving Milk:
 II. Filtration/Clarification:
III. Standardization:
IV. Fore warming/Pre-heating:
V. Addition of Sugar:
VI. Condensing:
VII. Homogenization:
VIII. Cooling and crystallization:
IX. Packaging:
X. Storage:
Evaluation of Condensed and Evaporated Milk-:
A. Score card-
B. Procedure for the Examination or Evaluation of both Condensed
and Evaporated milk-
i. Sampling – Select a can of the product at random for
examination.
ii. Sequence of Observations – Avoid undue agitation when
transporting the can to the laboratory.
Place it on the table for examination in the same upright
position as before.
Cut more than 3/4th of the top of the can and turn it back.
Then examine it in the following order:
Appearance of the can: Look for signs of rust, etc., both
outside and inside (when emptied).
Appearance of the product: Examine uniformity of color,
look for absence of lumps in condensed milk and cream
layer/butter particles/curd in evaporated milk.
Viscosity (body and texture): Observe whether the
viscosity is high, normal or low while pouring the contents
into a beaker.
Sediment: Watch for presence and absence of sediment
at the bottom of the container when emptied.
Flavor and Odor: Note defects, if any, by placing a small
spoonful of condensed milk or of diluted evaporated milk
(1:1 with distilled water) on the tongue.
Laboratory Tests: Take a suitable sample aseptically and
then test for fat, total solids, bacteria, sugar, adulterants
and preservatives, etc.
Requirements of high gade condensed and evaporated
milks: High quality condensed milk should have a clean,
pleasant aroma, a pronounced sweet taste, smooth and
 uniform body and texture, and a uniform light color,
which should be yellow for cow and light greenish white
for buffalo milk. High quality evaporated milk should have
a mild, pleasant flavor, a relatively viscous body and
uniformly smooth texture, and uniform color as described
for condensed milk.
Dried Milk:
Definition-:
Dried milk or milk powder is the product obtained by the removal of
water from milk by heat or other suitable means, to produce a solid
containing 5 per cent or less moisture.
Whole milk, defatted milk or skim milk may be used for drying.
The dried product obtained from whole milk is called Dried Whole Milk
or Whole Milk Powder (WMP) and that from skim milk is known as
Dried Skim Milk or Skim Milk Powder (SMP), or Non-Fat Dry Milk
(NFDM).
Methods of Manufacture of Skim Milk and Whole Milk Powder-: 1) By
Drum Process Method-
1. Whole milk powder
(a) Receiving milk: Only high-grade milk should be accepted.
(b) Filtration/clarification: The chief object of this is to remove
extraneous matter.
(c) Standardization: This is done to adjust the ratio of fat and solids-not-
fat in raw milk to meet the legal standards for composition in dried
whole milk. Raw milk is standardized by adding to it a calculated
amount of skim milk or cream.
(d) Fore warming: This is important for the destruction of micro-
organisms and inactivation of enzymes, and for improving the physical
quality of the finished product. Heating skim milk to 85°C for 10
minutes ensures good baking properties in the skim milk powder.
(e) Condensing: Normally a total solids of 16 to 18 per cent in the
condensed product is sought.
(f) Homogenization: The whole milk is usually homogenized after
concentration and before drying to reduce the proportion of free fat in
the dried product, thereby lowering the chances of oxidized flavor
development.
The homogenization is carried out at 63-77°C (145-170°F) in two stages,
2500 psi on the first stage and 500 psi on the second.
(g) Pre-heating: This increases the efficiency of drum drying. It is carried
out by heating the feed-concentrate to 74-85°C before pumping it into
the reservoir between the drums.
(h) Drum drying.
(j) Packaging.
(k) Storage.
2. Skim milk powder
Same as for whole milk powder except that 'standardization' and
'homogenization' are omitted, while 'clarification' is taken care of
during centrifugal cream separation.
2) By Spray Process-
1. Whole milk powder
(a) Receiving milk: Only high-grade milk should be accepted. (b)
Cooling. To preserve the quality of milk.
(c) Standardization.
(d) Pre-heating: For efficient filtration/clarification
(e) Filtration clarification: The chief object of this is to remove
extraneous matter. This operation can also be done before
standardization.
(f) Homogenization: Commonly done, if direct reconstitution of dry
whole milk is contemplated. Without homogenization, the fat may
churn during agitation while combining it with water.
Another merit of homogenization is improvement in the keeping
quality of the powder.
A pressure of 3000 psi (2500 psi on the first stage and 500 psi on the
second) at 63 to 74°C (145 to 165°F) is sufficient.
(g) Heat: This actually serves the purpose of fore warming/pre-
heating.
The main object is to prolong the shelf life of the dried product by
inactivation of lipase.
This pre-heating should also ensure pasteurization, thus reducing the
viable micro-organisms.
A beneficial influence on the heat-stability of the product may follow
from the pre-heat treatment.
Several optimum temperature-time combinations of heating in the
range of 82°C (180°F) for 15 minutes to 93°C (200°F) for 3 minutes
are used in commercial practice.
Note: Low heat-treatment minimizes cooked flavor development in
the product but does not develop anti-oxidants, which delay
oxidation in whole milk powder and thereby help improve its
keeping quality.
(h) Condensing. Normally a concentration of 35 to 45 per cent total
solids is produced, and the concentrate is continuously removed
from the evaporator with the help of a continuous density tester.
(j) Pre-heating: The temperature of the condensed milk after leaving
the evaporator is boosted to approximately 71°C (160°F) in a heat-
exchanger before being pumped, in order to increase the efficiency
of spray drying.
(k) Pumping: This forces the hot concentrate through the atomizer.
Generally, a pressure of 2500 psi is used.
(l) Spray drying: The concentrated milk is dried with inlet air at 143
to 232°C (300 to 450°F) and exit air at 74 to 93°C (165 to 200°F),
depending on product characteristics.
To reduce heat- damage during drying and yet obtain the desired
moisture, a low exhaust air temperature is preferred.
(m) Cooling: The dry whole milk should be removed promptly from
the hot air stream to maintain better flavor and body characteristics
and also keeping quality.
The higher the temperature and the longer the time the product is
above the melting point of fat the greater the amount of free fat
obtained, thus adversely affecting keeping quality.
Hence it is essential to cool the powder immediately to a
temperature below the melting point of fat.
(n) Sifting: A 12-mesh screen is used for sifting dry whole milk.
Note: The size of (powder) particles is designated by microns or
mesh.
A micron (μM) is one-millionth part of a meter, i.e. 0.001 mm.
Mesh refers to the number of screen openings per lineal inch.
The opening also depends upon the size of the wire used in making
the mesh material. The Tyler sieve, the U.S. scale sieve and the B.S.S.
sieve use different sizes of wire for making up the screen. A 100-
mesh Tyler sieve has an opening of 0.147 mm., which is equivalent to
147 μM; the 400-mesh opening is equivalent to a 38 μM diameter.
For smaller sizes, a microscopic analysis is made to determine the
particle diameter.
(p) Packaging.
(q) Storage.
2. Skim milk powder
(a) Receiving milk: Same as for WMP.
(b) Cooling: Same as for WMP.
(c) Pre-heating and separation: Cream can be separated with or
without pre-heating the milk: special cold milk separators are
required for the low-temperature method.
The most important consideration is a high degree of separation
efficiency (not more than 0.1 per cent fat in skim milk).
(d) Pasteurization:
I. Low heat skim milk powder:
Its manufacture requires that heating be carefully controlled during
pasteurization so as to produce the minimum number of heat-
induced changes.
Control of both temperature and time is important. Higher
temperature and/ or longer holding time contribute directly to whey
protein denaturation which is measured by whey protein nitrogen
(WPN) content per g. of powder.
It should have a WPN of 6 mg. or more.
II. High heat skim milk powder:
A higher heat treatment imparts good baking qualities to the
powder.
For this purpose, be sides pasteurizing at 71°C (161°F) for 15
seconds, the powder is pre-heated a second time at 85°C (185°F) for
20 minutes before being condensed.
Its WPN content should be no more than 1.5 mg.
(e) Condensing (see under whole milk powder):
Normally a concentration of 40 to 42 per cent total solids is
obtained.
(f) Re-heating (see under whole milk powder): This is done to
increase the efficiency of drying.
(g) Filtration: This is done to remove any extraneous matter from the
concentrate before atomization, so that it can function smoothly.
(h) Pumping (see under whole milk powder): This is done to force the
hot concentrate through the atomizer.
(j) Spray drying (see under whole milk powder): Low heat skim milk
powder is dried up to 3 to 4 per cent moisture, while high heat skim
milk powder usually has not more than 3.5 per cent moisture.
(k) Cooling: Most milk driers have a continuous removal system to
immediately separate the dry product from the hot air stream.
 The dry product should be cooled at once. If the skim milk powder is
too hot when packaged, it may become lumpy due to 'heat-caking,
and development of storage defects in flavor and color may be rapid.
(l) Sifting: A 25-mesh screen is commonly used for sifting dry skim
milk (see under whole milk powder).
(m) Packaging.
(n) Storage.
Instantization:
Definition:
Instantization refers to the process by which dried milk and milk
products are made instant-soluble.
Purpose:
The chief purpose of instantizing is to improve the rate and
completeness of the reconstitutability of dry milk and milk products.
The instantizing process affects wettability, sinkability, dispersability
and solubility of the particles. However, total solubility is not improved.
Products:
Mainly applied to skim milk powder/non-fat dried milk. However,
whole milk powder and other milk fat containing dry dairy products are
also being instantized.
Characteristics:
(1) Lowers bulk density and hence increases packaging costs.
(2) Increases moisture content of the finished pro- duct, which
lowers the keeping quality.
Factors influencing instantization:
Dry milk that is manufactured especially for instantization usually yields
the best results.
Moisture content and particle size should be as uniform as possible.
A minimum of fine particles, less than 20μM in diameter, is desired,
while particles in the range of 25 to 50μM are preferred.
The skim milk powder for agglomeration should be low in fat content.
Low heat or medium heat skim milk powder is normally used, since high
heat skim milk powder shatters much more easily in handling after
instantization.
Physio-Chemical Properties of Dried Milk Powders:
Physio-Chemical Properties include - Particle size, surface and shape,
structure, density, flowability, dustiness and reconstitutability, flavour,
colour and appearance.
Evaluation of Dried Milk Powders:
Evaluation process is done in 3 main steps.
1) Sampling:
Select a can of the product at random for examination.
 2) Sequence of observations:
Cut more than three-fourths of the top of the can and turn it back.
Then examine it in the following order:
(i) Appearance of the can: Look out for signs of rust, etc., both
outside and inside (when emptied).
(ii) Flavor: Note the smell (odor) immediately on opening the can.
Then reconstitute with distilled water to the original
concentration (according to directions given on the can-label) and
after about an hour examine flavor (smell and taste) by tasting 5-
10 ml on the tongue.
(iii) Appearance of the product: Examine uniformity of color and
absence of lumps, foreign specks, scorched/burnt particles, etc.
(iv) Fineness and homogeneity (body and texture): Pour the
product from the can into another container and note the flow
characteristics.
3) Requirements of high-grade whole milk powder and skim milk
powder:
The physical (sensory) qualities of high-grade milk powder will chiefly
depend on the method of drying, viz., roller or spray, and also to some
extent on whether they have been prepared from cow or buffalo milk
and whole or skim milk.
Spray-dried whole milk should be clean, rich, sweet and very pleasant
in flavor, fine, smooth and homogeneous in body and texture, uniform
in color which should be normally light yellow for cow and creamy
white for buffalo and devoid of foreign specks, and scorched or burnt
particles.
Skim milk powder, when reconstituted, should be similar in flavor to
that of fresh skim milk for a spray product, although it may possess a
slightly cooked or heated flavor for a roller-dried product, it should be
fine, smooth and homogeneous in body and texture if produced by the
spray process, but may be coarse and less homogeneous if produced by
the roller process.
If not finely pulverized, it should be uniformly yellowish white for cow
and chalky white for buffalo milk, foreign specks, and scorched or burnt
particles should be absent.
Defects in Dried Milk Powders:
Defects in whole milk powder and skim milk powder may arise due to
low quality milk and faulty methods in the manufacture and storage of
these products.
Their causes and prevention are given below:
Cream:
Definition-:

Cream may be defined as:

(i) that portion of milk which is rich in milk fat', or
(ii) that portion of milk into which has been gathered and which
contains a large portion of milk fat', or
(iii) 'when milk fat is concentrated into a fraction of the original milk,
that portion is known as cream'.
According to the PFA Rules (1976), cream, excluding sterilized cream, is
the product of cow or buffalo milk or a combination thereof which
contains not less than 25 per cent milk fat.
Classification-:
Cream is not a definite specific substance. It contains all the milk
constituents but in varying proportions.
The milk fat in cream may vary from 18 to 85 per cent, the solids-not-
fat constituents occur in lower proportions than in milk.
Cream may be classified broadly as: (a) market cream: Which is used for
direct consumption, and
(b) manufacturing cream: Which is used for the manufacture of dairy
products.
The various types of cream are:
(i) Table cream (containing 20-25 per cent milk fat)
(ii) Light cream (containing 20-25 per cent milk fat)
(iii) Coffee cream (containing 20-25 per cent milk fat)
(iv) Whipping cream (containing 30-40 per cent milk fat)
(v) Heavy cream (containing 30-40 per cent milk fat)
(vi) Plastic cream (containing 65-85 per cent milk fat)
Composition-:
The chemical composition of 2 specific creams are given below
Percentage
Constituents
i ii
Water 68.20 45.45
Fat 25 50
Protein 2.54 1.69
Lactose 3.71 2.47
Ash 0.56 0.37
Total Solids 31.8 54.55
Solids-not-fat 6.8 4.55

The higher the fat percentage in cream, the lower the solids-not-fat
content.
The formula for determining the percentage of solids-not- fat in cream
is:
100−%fat ∈cream
% SNF in cream = 100−%fat ∈milk
× %SNF in milk.

Cream Separation-:
1. The process of separating the suspended particles of a substance
from a liquid in a mixture by churning them at high speed is called
centrifugation.
2. The cream is separated from the milk by centrifugation.
3. Centrifugation works on the principle that the dense particles are
forced to move to the bottom and the lighter particles stay at the
top of the test tube when spinning rapidly.
4. To carry out this the milk is rotated at a very high speed in a
centrifuge machine.
 5. The cream being lighter floats over the heavier milk.
6. The cream formed is removed and leaves behind the fat-free milk.
Therefore, the cream can be separated from milk by the process of
centrifugation.
There are two methods of cream separation viz.,
· Gravity Method
· Centrifugal Method
Cream separation by gravity method:
When milk is allowed to stand undisturbed for some time, there is a
tendency of fat to rise. The velocity or rate at which the fat globules rise
is given by the following equation, which is known as Stoke’s Law:
V = (2/9) * Gr2 * (ds - df) / N
Where,
V = rate of rise of fat globule in centimeter per seconds
r = radius of fat globule
G = Force of gravity (981 dynes)
ƞ= Viscosity of skim milk
ds = density of skim milk
df = density of fat globule
From, Stoke’s Law it is observed that theoretically velocity increases
with:
a. Increasing radius of fat globule,
b. Increasing difference in densities of skim milk and fat
c. Decreasing viscosity of skim milk
There are five various methods for separating the cream using gravity
method:
i. Shallow Pan Method: Milk is allowed to stand in a pan of 10 cm
depth and 45-60 cm diameter at 7°C for 24 h. During this time, cream
rises to the surface.
ii. Deep Pan Method: Milk is allowed to stand in pan of 20” depth and 8
to 12” diameter at 10°C for 24 h. These tall cans have glass on one side
of can and a faucet placed near the bottom. Skim milk is drawn through
the faucet.
iii. Water Dilution Method: Milk is diluted with water and allows
standing for 12 h at 37.7°C temperature. Water would make the milk
less viscous, thus facilitating the rising of the fat globules.
iv. Scalding Method: Heating and cooling of milk slowly causes the
formation of cream layer at surface of milk
v. Jersey Creamery Method: Milk is heated to 40°C using hot water in
the jacketed vat and then cool to 10°C using chilled water in place of
hot water in the jacket of Vat. The cream will be separated rapidly on
cooling, immediately after heating the milk, by increasing the difference
in densities of milk fat and serum.
Gravity method being very slow, it is no longer used commercially for
cream separation.
Cream separation by centrifugal method:
Milk is fed to machine through flow regulator. Milk comes to regulating
chamber from milk basin by milk faucet. When milk enters the
revolving bowl through milk regulator of machine, it is subjected to a
gravity and centrifugal force. Centrifugal force is about 3000 to 6000
times more than gravitational force. Fat (0.9) and skim milk (1.037) are
varying in their specific gravity. When fat and skim milk are subjected to
centrifugal force, the difference in density affect the fat and skim milk
i.e. (heavier Portion) affected more intensely than the fat (lighter
portion). So skim milk is forced to the periphery and fat portion (cream)
moves towards the centre. Cream and skim milk forms separated
vertical walls within the bowl and goes out through separate outlets
near the axis of rotation. The cream outlet is at higher level than skim
milk outlet. The rate or movement of a fat globule in machine is
estimated by following Stoke’s equation.
V = r2 *((as - df) / n) * N2 * R * K
Where,
V = rate of movement of a single fat globule
r = radius of fat globule
ds = density of skim milk
df = density of fat
N = Revolution per minute of bowl
R = Distance of fat globule from axis of rotation.
K = Constant
N = Viscosity of skim milk
It will be seen from the above that the speed (rate) of cream separation
is increased by:
· greater radius of the fat globule
· greater difference in density between skim milk and fat
· greater speed of the bowl
· greater size of the bowl
· lower viscosity of skim milk
4.3 Characteristics of gravity and centrifugal methods
Gravity and centrifugal cream separation compare as shown below:

Particulars Gravity Centrifugal Method

Method
Nature of force causing Gravitational
Centrifugal force
Separation force
Extremely Practically
Speed of separation
slow instantaneous
Direction of movement of fat
Vertical Horizontal
and skim milk particles
Bacteriological quality of
Low High
cream or skim milk
Fat % of cream 10-25% only 18-85 %
Skim milk 0.2 % above 0.1 or below
Scale of operation Small Large
not more than
Fat % recovered in cream 99-99.5
90
Sampling of Cream-:
GENERAL REQUIREMENTS WHILE SAMPLING-
Sample shall be drawn by an experienced person in a protected place
not exposed to damp, air, bright light, dust, soot or smoke particles,
rain etc.
The sample temperature while sampling should be between 0 to 15°C.
If sample is to be transported, the sample temperature should be
maintained between 0-7°C (for ice cream -15°C)
• Precautions shall be taken to protect the samples, the material being
samples, the sampling instruments and containers for sample from
adventitious contamination and adulteration.
• The sampling instruments and sample containers shall be clean, dry
and shall not impart any foreign odour, or flavor.
• The sampling appliances used shall be of stainless steel (SS) or of
suitable material and shall be light in weight for the operator to be able
to move them rapidly through the product. All the surfaces of sampling
appliances shall be rounded.
• The sample containers shall be of such size that sufficient head space
is allowed for expansion at the top. At the same time, this space should
not be too large as air exerts detrimental action.
• Each container shall be sealed air tight after filling and marked with
full details of sampling or code number, name and address of
manufacturer and other important consignment.
• Plunger
• Sampling bottle
• Dipper
CARE OF SAMPLES-
• The samples shall be sent to the examining laboratory as soon as
possible, and it shall be analysed without delay.
• If not possible, the sample(s) shall be stored in a refrigerated
temperature 0 to 5°C, where this is not possible, then adequate
precautions shall be taken to prevent deterioration and exposure to
high temperature and light.
In some cases, preservative may be added to prevent deterioration and
it does not interfere with the subsequent analysis.
• The preservative added shall be indicated on the label of sample
botles. According to FSSAI (2015), the preservative used in the case of
sample of milk, in liquid form commonly known as "formalin" i.e.
Formalin containing about 40 per cent of formaldehyde in aqueous
solution in proportion of 0.4 ml (two drops) for 100 ml or 100 grams.
CREAM SAMPLING-
• The sampling procedure followed for milk like in individual, several or
bulk containers can be applied to cream.
• When samples of cream is thin and in small containers, it shall be
mixed by plunging not less than 10 times.
• It is essential that whole cream should be thoroughly agitated and to
mixed. For thick cream, plunger can be used for proper mixing.
• To avoid whipping and churning, the disc of the plunger shall not be
brought above the surface of the cream.
PREPARATION OF CREAM SAMPLE-
• When cream is thin and in small containers, it shall be mixed by
plunging atleast ten times.
• The position of the plunger shall be moved from place to place to
ensure that the whole of the cream at the bottom of the vessel has
been thoroughly agitated and mixed with the upper layer.
To avoid whipping and churning, the disc of the plunger shall not be
brought above the surface of the cream.
• When cream is thick or in bulk containers, it shall be mixed by
plunging as same for thin cream.
• When the cream is sour, the material shall be warmed so as to attain
a temperature between 30° and 40°C and, while cooling it to room
temperature, the container shaken gently or the contents stirred. Keep
the contents covered as much as possible.
• In all cases the sample of cream shall be taken immediately after
mixing.
Neutralization of Cream For Butter Making-:
Neutralization of sour cream for butter making refers to partial
reduction in its acidity.
OBJECTIVE-
1.To avoid excessive fat loss in buttermilk, due to churning of high acid
pasteurized cream.
2.To guard against off flavors in cream.
3.To improve the keeping quality of butter made from high acid cream.
BUTTER IS GENERALLY STORED AT -23⁰C TO -29⁰C
PROCEDURE FOR NEUTRALIZATION-
1.ADOPTION OF DEFINITE STANDARD OF CHURNING ACIDITY:
*Butter for long storage –cream acidity should be 0.06 to 0.08
*Butter for short storage-cream acidity should be 0.25 to 0.30.
2.TESTING CORRECTLY FOR ACIDITY:
*Take sample after thorough mixing
*Heat cream to boiling point for one minute before testing for acidity
*First partially neutralize the cream with known amount of alkali and
then treat as above (for acid cream)
*Determine lactic acidity of cream by titration of a fixed weight (10g)
with the standard alkali (n/9 NaOH solution), using phenolphthalein as
an indicator.
 The practical value of sodium bicarbonate neutralizer used is
lower than theoretical value due to the presence of variable
amount of carbon-dioxide which raises the titrable value.
 Carbon dioxide doesn’t react with sodium bicarbonate neutralizer
and consequently results in over neutralization.
 The actual neutralizing capacity of Lime is only 80 percent of the
amount used, since nearly 20 % of it reacts with casein and
phosphate, and so is not available for acid neutralization.
CORRECT PROCEDURE FOR ADDITION OF NEUTRALIZER-
 Should never be added dry
 Should be diluted 10-15 times in clean portable water
 Should be mixed uniformly and stirred vigorously
 Temperature of cream should be around 29⁰C to 32⁰C, during
addition of neutralizer
 Stirring should be continued for 5-10 minutes after adding
neutralizer
 Then cream should be pasteurized
DOUBLE NEUTRATIZATION OF CREAM WITH LIME AND SODA-
 First use lime as neutralizer to bring the cream acidity down to 0.3
-0.4% L.A.
  Next use soda neutralizer to bring the cream acidity to desired
level.
Objectives
 To reduce intense flavor effect of single neutralizer used whether
lime or soda
 To avoid production of excessive carbon dioxide by the use of
sodium bicarbonate with high acid cream.
Sterilization of Cream-:
Sterilization of cream improves the shelf life of cream by making it free
from viable organisms. In-can sterilization of cream is done in retorts.
The filled cans or bottles are packed in retorts/batch sterilizer and then
heated allowing 15 minutes for coming up time to desired temperature
(118°C), 12-15 minutes holding time at 118°C and 15 minutes for
cooling to room temperature. Thus, it takes 45 minutes to complete
one cycle of sterilization process for one batch. After completion of the
process the tins/bottles are cleaned and tested for leakage by a
immersing them in clean water. Leaking tins/bottles are then discarded
separately.
Pasteurization of Cream-:
Definition: Pasteurization of cream refers to the process heating every
particle of cream to not less than 71°C (160°F) and holding it at such a
temperature for at least 20 minutes, or to any suitable temperature-
time combination, using approved and properly-operated equipment.
Objectives:
(i)To destroy the pathogenic micro-organisms in cream so as to make it,
and also the resultant butter, safe for human consumption.
(ii) To destroy undesirable micro-organisms and inactivate the enzymes
present, so as to prolong the keeping qualities of the cream and butter.
(iii) To complete the neutralization process;
(iv) To eliminate some of the gaseous tainting substances.
(v) To make possible the removal of some volatile off-flavors (such as
feed and weed flavors) during vacreation.
Methods:
(i) Holder pasteurization: This is a batch process used for small- scale
handling. The cream is heated in a batch/holder pasteurizer to 71°C
(160°F) for 20 minutes and then promptly cooled. (A multi- processing
vat may be used for cream pasteurization and cooling.
(ii) HTST (Plate) pasteurization: This is a continuous process used for
large-scale handling. It allows for much greater regeneration than
would be possible with any other process. The plate pasteurizer is
better suited to freshly-separated sweet cream than neutralized cream,
as the latter more easily forms burnt-on films on the plates. The
maximum heating temperature may be 95-100°C (203-212°F) for 15-16
seconds.
(iii) Vacuum pasteurization (vacreation): This is also a continuous
process. A noteworthy characteristic of vacuum pasteurization is that a
dilution of the initial cream takes place and the fat test may be lowered
by 6 to 8 per cent; this fact has to be kept in view when standardizing
cream.
Cooling of Cream-:
Regenerative Heater Coolers:
1. As part of HTST pasteurization process, regenerative cooling of cream
is followed by final cooling by means of chilled water.
2. Regenerative heater coolers is based on reciprocating heat
exchanges between the hot outgoing and the cold incoming cream.
3. When using a combination of intra-tube heater and surface cooler,
hot cream flows up through the inside of the pipe unit and the cold
cream flows down over the outside of the pipe unit. The incoming cold
cream is thus heated by the hot cream coming from the pasteurizer,
and out flowing hot cream is cooled by the cold, raw cream flowing to
the pasteurizer.
4. Under average conditions, the temperature of the cold cream is thus
raised by about 12-15 C by hot cream and temperature of hot cream is
lowered approximately 12-15 C by the cold cream, thus accomplishing a
considerable saving of heat energy.
Surface Cooler:
1. Highly suitable for the cooling of flash-pasteurized cream.
2. Surface cooler comprises two corrugated/undulated SS plates
providing horizontal passages for cooling water or liquid refrigerant
between the plates. The cream allowed to flow from top reservoir over
the outside of the plates gets cooled. The surface cooler is usually
confined to two sections, each arranged with independent in-take and
out-flow for the refrigerant. The upper section is cooled with water and
lower section with brine/ direct expansion ammonia.
3. Advantage: Aeration of the cream.
4. Drawback: Surface cooler breaks the closed system of cream flow.
Internal Tube Cooler:
1. It consists of the two-tube principles, one inside of the other.
2. The cream flows through the inner tube, while the refrigerant flows
in counter current between the inner and outer tubes.
3. The usual unit consists of one or two sections for water and one
section for brine or direct expansion ammonia.
4. Advantage: Preserving the unbroken, closed system of cream flow,
discharging the cream into the vats and up to any reasonable elevation
without the need of a pump at the discharge end of the cooler.
5. The internal tube cooler does not subject the cream to aeration. If
aeration is desired it should be provided before the cream reaches this
cooler
Evaluation of Cream-:
Procedure of Evaluation of Cream-
(1) Sampling.
(2) Sequence of observations: Carefully transfer bottle/container from
refrigerator/cold room (5-10°C/40-50°F) to the laboratory in a vertical
position, avoiding undue agitation. Then examine in the following
order:
(i) Take note of serum separation.
(ii) Take note of sediment at the bottom of the bottle.
(iii) Observe container and closure for fullness, cleanliness and general
appearance.
(iv) Take note of cream plug, if any.
(v) Secure representative sample for bacterial count (aseptically by
standard procedures), to be used later for other tests.
(vi) Temper cream to 10°C (50°F) and determine viscosity.
(vii) Take about 20 ml cream in a 100 ml beaker.
Warm it to 15-21°C (60-70°F) and note the smell.
Then put some cream in the mouth and note the taste.
(viii) Determine percentage of titratable acidity and fat.
(ix) Test for defects such as oiling-off, feathering in coffee, etc.
(3) Requirements of high-grade table cream:
High quality table cream should have a clean, sweet, pleasant, nutty
flavor.
The body should be smooth, uniform and reasonably viscous for the
percentage of fat present.
The physical appearance should be good.
MANUFACTURING CREAM-
Requirements for high grade product: Sweet cream, which is to be
processed or manufactured into other dairy products, should be of a
high quality.
The cream should have a low acidity and clean flavor, should be fresh
and delivered to the dairy factory in a clean, sanitary container
adequately protected from contamination and against heat in transit.
Defects in Cream, Their Causes and Prevention-:

Defects in cream may arise from low grade milk and faulty methods of
production, processing and storage. The common defects in both table
and manufacturing creams, their causes and prevention, are