Module.
4 Sensory evaluation of milk
Lesson-14
Judging and Grading of Milk
14.1. INTRODUCTION
The sensory evaluation of milk is of utmost importance. Packaged and retail sale of fresh milk
comprises a major share of Indian dairy industry (both in the organised and unorganised sectors).
Since fluid milk is consumed by almost everyone, everyday it is being assessed daily for its
quality. If the flavour of milk is not appealing or appetizing less of it will be consumed.
The sensory characteristics of any dairy product is dependent on the quality attributes of milk
used. If the raw milk supply is properly assessed for its sensory quality, all off flavour defects
due to raw milk could be minimized if not eliminated.
Among dairy product judges the scoring or differentiation of milk into different quality classes
demands keener, more fully developed senses of smell and taste than in the sensory evaluation of
other dairy products. Many of the off-flavours present in fluid milk are more delicate, less
volatile or more elusive than those present in other milk products.
Milk, may be raw or pasteurized, skim or whole, toned or double toned, standardized or full-fat,
cow or buffalo. In this lesson the term ‘milk’ would mean PASTEURIZED, STANDARDIZED
(MIXED) MILK unless otherwise specified. Pasteurization is effected by heating the milk to
72°C for 15 sec and 63°C for 30 min in HTST and LTLT respectively.
Judging and grading of milk
PASTEURIZED milk commonly possesses some degree of a heated or cooked flavour especially
immediately after processing, but the intensity of cooked flavour diminishes during storage. The
flavour of milk is affected by:
Heating-up and cooling time
Temperature difference between the product and heating medium
Velocity of the product in a continuous system
Occurrence of product 'burn on', and
Direct vs. indirect heating methods.
The flavour of pasteurized unhomogenized milk undergoes flavour changes during storage as
below:
HEATED-> NORMAL-> FLAT -> METALLlC--> OXIDISED
The extent of flavour deterioration depends on the storage time, season of the year, type
of roughage fed to the cow and buffaloes and relative levels of cupric or ferric ions.
14.2. MILK SCORE CARD
The original score card (100 point scale) developed by the ADSA has been extensively modified.
The BIS score card for milk is given in Table 14.1. Familiarity with the score card and use of
score card guide is important for milk product judging.
Judging and grading of milk
Table-14.1: BIS Score card for milk
A. Assign score for each sample for different characteristics.
CHARACTERISTICS MAXIMUM SCORE SAMPLE SCORE
Colour & appearance 10
Odour 20
Flavour 40
Body 30
B. Indicate the degree of defects such as the following. Encircle the one applicable
and deduct from appropriate attributes.
CHARACTERISTICS DEFECT DEGREE OF DEFECT
Suspicion Slight Pronounced
Colour & appearance Suspended particles, 2 4 10
filth, foreign matter,
bloody
Odour stale, acidic, abnormal 5 10 15
Flavour Cooked, oxidized, 5 10 20
rancid, metallic,
neutralizer, feed,
barny, cowy, flavour
defects due to
adulterants and other
additives.
Body Watery, ropy, curdy 5 10 20
Judging and grading of milk
Table-14.2. Suggested scoring guide for flavour for milk
Intensity of flavour defect
Slight Moderate Definite Strong Pronounced
Astringent 8 7 6 - -
Barny 5 4 3 2 1-0
Bitter 5 4 3 2 1-0
Cooked 9 8 7 6 5-0
Cowy 6 5 4 3 2-0
Feed 9 8 7 6 5-0
Fermented/fruity 3 2 1 0 0
Flat 9 8 7 - -
Foreign 3 2 1 0 0
Garlic/onion 5 4 3 2 1-0
High acid 3 2 1 0 0
Lacks freshness 8 7 6 0 0
Malty 5 4 3 2 1-0
Metallic 5 4 3 2 1-0
Oxidised
Light induced 6 5 4 3 2-0
Metal induced 5 4 3 2 1-0
Rancid 4 3 2 1 0
Salty 8 7 6 5 4-0
Unclean 3 2 1 0 0
(Source IS: 7768-1975)
14.3. GRADING
After computation of data the following grades should be awarded. Any attribute showing
pronounced defect should be graded poor and rejected
Quality of milk Scores obtained Grade of milk
Excellent 90 and above A
Good 80 to 89 B
Fair 60 to 79 C
Poor 59 and below D
Judging and grading of milk
14.4. MILK SCORING TECHNIQUES
14.4.1. Preparation of samples for evaluation
This depends on the purpose or objective of evaluation, number of participants and the quality
criteria to be assessed. If several persons are to judge the milk samples for flavour, container and
closure and other criteria then several containers of each individual lot of milk must be provided.
14.4.2. Order of examination and scoring
a) Closure
Closure should be carefully observed. Nowadays bottles or cartons (not used in India) are not the
usual packaging material. The milk is being packaged in polyethylene sachets. Hence the
evaluator must see that the packaging properly sealed to prevent leakage/pilferage.
b) Container
Container as stated above, since plastic bags are now in vogue; these should be examined for
extent of fullness, cleanliness and freedom from cuts/nicks/pinholes from leakage.
c) Evaluation of milk flavour
The milk should be properly tempered between 13 to 18°C preferably 15.5˚C. Milk samples
should be poured into clean, odourless glasses paper/plastic cups. 10 to 15 ml milk should be
poured and a sip taken, rolled around the mouth and flavour sensation noted and then
expectorated. Sometimes, any aftertaste may be enhanced by drawing a breath of fresh air very
slowly through the mouth and then exhaling through the nose slowly. A full WHIFF of air
should be taken soon after the sample is placed in the container for any off-odour that may be
present.
Typically the flavour of milk should be “PLEASANTLY SWEET AND POSSESS
NEITHER A FORETASTE NOR AN AFTERTASTE” other then that imparted by the natural
richness due to milk fat and milk solids. When milk clearly exhibits the so-called TASTE there
is usually something WRONG with the flavour of the milk sample. Thus milk is considered to
have a defect if it has an odour, fore or after-taste and does not leave the mouth in clean, sweet
pleasant condition following tasting. The scoring guide lists most frequently observed off-
flavours. The defects should be described while scoring.
Judging and grading of milk
14.4.4. Undesirable flavours
a) Acid: Sour detected by taste and smell-due to microbial conversion of lactose to lactic acid
which imparts a tingling effect.
b) Astringent:Not common in milk
c) Barny: Transmitted off- flavour due to poor ventilation, foul smelling environment. Perceived
by sniffing and tasting. Characteristic aftertaste.
d) Bitter: Associated with other defects like astringency, rancidity due to weeds and microbial
(psychrotrophs) growth.
e) Cooked: Heat-induced. Appears when milk is heated to 76°C or more. There are 4 types of
heat-induced flavours: COOKED/SULPHUROUS; HEATED OR RICH; CARAMELISED and
SCORCHED. Heated and cooked flavours are easily identified, reaction time is quick, sensation
remains after expectoration. Cooked flavour may also be noted through smell.
f) Cowy (acetone): Distinct, persistent unpleasant, medicinal chemical aftertaste with acetone
bodies in milk i.e. ketosis in cows.
g) Feed: Imparts aromatic taints to milk when fed ½ - 3 h prior to milking. The off-flavour is
aromatic sometimes pleasant (e.g. alfa-alfa), detected by smell varies with feed. To prevent such
feeds should not be fed 3 h prior to milking.
h) Fermented/Fruity: Resembles vinegar, pineapple and apple. Found in old pasteurized milk,
due to growth of Pseudomonas spp. (P. fragii).
i) Flat: Bland in taste, lacks mouthfeel and lacks sweetness
j) Foreign: Can be detected by smell or taste due to chemicals/detergents, disinfectants,
sanitizers, exposure to fumes of petrol, diesel, kerosene, insecticides, ointments, medication to
cows etc.
Judging and grading of milk
k) Garlic/Onion (weedy): Pungent odour and persistent aftertaste.
l) Lacks freshness (stale): Taste reaction indicates loss of fine pleasing taste, slightly chalky.
May be 'forerunner' of either oxidised or rancid off-flavour or off-flavour caused by
psychrotrophs.
m) Malty: Flavour definite or pronounced, suggestive of malt caused by the growth of S. lactis
var maltigenes at > 18.2°C for 2-3 h can be smelled or tasted. Bacterial population in millions,
followed by acid/sour taste.
n) Metal-induced oxidised off- flavour: Due to lipid oxidation-metal catalyzed. Metallic, oily,
cardboardy, happy, stale, tallowy, painty and fishy are used to describe this off-flavour. The off-
flavour is quickly perceived in the mouth and has a relatively short adaptation time.
o) Light-induced oxidized off-flavour: Described as burnt, burnt protein, burnt feathers,
cabbagy, medicinal or chemical-like, light-activated or sunlight flavour or sunshine flavour, light
catalyzed lipid oxidation as well as protein degradation both are involved. It requires riboflavin
which is naturally present in milk. Homogenized milk is more susceptible but is resistant to
oxidized off-flavour (due to lipid oxidation) the opposite is true for non-homogenized milk.
p) Rancid:Extremely unpleasant, due to volatile fatty acids formed through enzymatic
hydrolysis of fat. Soapy, bitter and unclean aftertaste. Flavour is nauseating and revolting.
q) Salty: Perceived quickly in the mouth
r) Unclean: Due to the growth/ activity of psychrotrophs at >7.2 ° C.
Judging and grading of milk
Questions
1. In a score card of milk, maximum score allotted to
A. Appearance
B. Odour
C. Flavour
D. Body
2. Excellent quality milk score as BIS grading is
A. 90 and above
B. 80 to 89
C. 60 to79
D. 59 and below
3. The off flavour transmitted due to poor ventilation and foul smelling environment is
A. Cowy
B. Barny
C. Uunclean
D. Feed
4. Which one of the following is not a heat induced flavour
A. Cooked
B. Scorched
C. Caramel
D. Bitter
5. Feed imparts aromatic taints to milk when animal is fed
A. 1/2 - 3 h prior to milking
B. 3- 6 h prior to milking
C. 6- 7 h prior to milking
D. 7- 8 h prior to milking
