3. WHAT IS MILK?
A white liquid extracted from the mammary
gland of mammals.
The first food and nutrition for the young.
Produced after the gestation period
A complete food.
In India, milk is usually from from cow or buffalo
5. TYPES OF MILK FAT SNF
Standardized milk 4.5 8.5
Toned Milk 3.0 8.5
Double Toned milk 1.5 9.0
Skimmed Milk Not more than 0.5
percent
8.7
6. COLOR
The color of milk is perceived by consumers to be indicative of purity
and richness. Its white color is due to the scattering of reflected light
by the inherent ultramicroscopic particles, fat globules, colloidal
casein micelles, and calcium phosphate.
The intensity of white color is directly proportional to the size and
number of particles in suspension. Homogenization increases the
surface area of globules significantly as a result of the breakup of
larger globules. Accordingly, homogenized milk and cream are whiter
than their unhomogenized counterparts. Lack of fat globules gives
skim milk a blue tinge.
Cow's milk contains the pigments carotene and xanthophyll, which
tend to give a golden yellow color to the milkfat.
7. FLAVOUR
The flavor of milk is a property difficult to define, but there is no doubt that
taste and aroma are critical to the assessment of milk. Flavor constitutes a
critical criterion of quality for the consumer. It is a sensory property in which
odor and taste interact. The sweet taste of lactose is balanced against the
salty taste of chloride, and both are somewhat moderated by proteins. This
balance is maintained over a fairly wide range of milk composition even when
the chloride ion level varies from 0.06 to 0.12%.Saltiness can be detected by
sensory tests in samples containing 0.12% or more of chloride ions and
becomes marked in samples containing0.15%.
Although milk has a clean, pleasantly sweet flavor, it is quite bland, and
therefore any off-flavors are readily discernible. Off-flavors result when the
balance of flavor compounds is altered by micro-biological action, dairy farm
or processing conditions, or chemical or biochemical reactions.
8. DENSITY AND SPECIFIC GRAVITY
he density of milk with 3–5% fat averages 1.032g/cm3.
Accordingly, the weight of 1 L of milk is1.03 kg. To convert
the weight of milk from kilo-grams per liter to pounds per
gallon, the number is multiplied by 8.34.
The average specific gravity of milk at 15.5°C(60°F) is
1.032. It varies from 1.028 to 1.035 in commercial milk.
The specific gravities of milkfat(0.93), MSNF (1.62), and
water (1.0) determine the specific gravity of milk.
Specific gravity is increased by the removal of fat and
lowered by the addition of water.
9. SURFACE TENSION
Surface properties are involved in adsorption phenomena and the formation
and stability of emulsions. They are relevant to creaming, fat globule
membrane function, foaming, and emulsifier use in dairy products.
Normal cow’s milk has an inherent surface activity. Its sur-face tension
approximates 70% of that of water. The surface tension of whole milk is
usually about 50–52 MN/m (or dyn/cm) at 20°C.The surface tension of skim
milk is 55–60 mN/m. For cream, it is approximately 46–47 mN/m (8,9).
Fat reduces surface tension by a physical effect. Lactose and most of the salts
tend to raise it when they are present in true solution. Surface tension
decreases as milk temperature rises. Processing treatments such as heating,
homogenization, and shear tend to increase surface tension.
10. VISCOSITY
Whole milk and skim milk display viscosities of 2.0–2.1 and1.5–1.8 cP (or
mPa/sec) at 20°C, respectively. The viscosity of milk and cream creates the
impression of “richness” to the consumer. From an organoleptic stand-point,
viscosity contributes to mouthfeel and flavor release.
Alterations in the size of any dispersed constituents result in viscosity
changes. When fat globules are greatly subdivided by homogenization, an
increase in viscosity is observed.
The viscosity of skim milk decreases on heating to 62°C, after which it
increases apparently due to changes in protein hydration. An increase of
temperature causes a marked reduction of viscosity. For example, at20°C,
milk is about half as viscous as at 0°C and at 40°C is approximately one-third
of the value at 0°C.
11. SPESCIFIC HEAT
The specific heat of milk products is a function of their composition. The values for
whole milk, skim milk, 40% cream, butter at 15°C are 0.93, 0.95, 0.68, 0.53,
BTU/lb•°F, respectively (3.89, 3.97, 3.35, 2.21, and 4.06 kJ/kg•K, respectively).
ELECTRICAL CONDUCTIVITY
Current passes through the milk by virtue of the activity of its ionic mineral
constituents, of which the chloride ions carry 60–68%of the current. There is therefore a
close correlation between the electrical conductivity of milk and its chloride content.
The electrical conductivity of normal milk corresponds to that of approximately 0.25%
sodium chloride solution (w/w) and ranges from 45 to 45–55 x 10–4mho.The progress of
fermentation can be followed by increases in the conductivity of the yogurt base. Also,
demineralization of whey and its fractions, leading to loss of ionic minerals, is
monitored using a conductivity meter.
12. FREEZING POINT
Determination of freezing point is a parameter widely used in the industry for
detection of adulteration of milk with water. The freezing point of milk has a
relatively narrow range (from –0.520 to–0.560°C, the average being –
0.540°C).Addition of water raises the freezing point, and readings above –
0.520 support strong suspicion of watering the milk. As little as 3% water
added to milk can be detected by this method.
BOILING POINT
A solution boils at a higher temperature than does the pure solvent, according
to the concentration of the dissolved substance. The boiling point of milk is
100.17°C. The milk constituents in true solution are mainly responsible for
the elevation of the boiling point above 100°C. Elevation of the boiling point
is based on the same principles as depression of freezing point. However, for
detecting added water, the freezing point method is far superior on the
grounds of accuracy and convenience.
13. REFRACTIVITY
The refraction of light by a solution is a function of the molecular
concentration of the solute in solution. Each solute maintains its own
refractivity, and the refractive index of a mixture is that of the total of the
refractive indices of the substances plus that of the solvent. The components
of milk contributing to its refractive index in descending order of importance
are water, proteins, lactose, and minor constituents. The refractive index of
milk at 20°C is 1.3440–1.3485.The refractive index of butterfat is distinct
enough to indicate its authenticity.
15. Cream
Cream is the top most layer of the whole milk which is not homogenized, most of the fat
globules in the milk aggregate and come on the top as fat is lighter than rest of the milk and
form a creamy layer. When this layer is trimmed down from the milk remaining part is known
as skimmed milk and the excluded fatty layer is called cream.
Composition of Cream
• Water 68%
• Carbohydrates (lactose) 3.2%
• Fats 25%
• Proteins 2%
• Minerals (ash) 0.1%
16. Yogurt (curd in India)
The carbohydrate of milk (lactose) is fermented and the acid thus produced is
responsible for coagulation of casein protein and tangy taste. Coagulation of
protein forces some of the water in the milk to the top which also contains
some whey proteins and fermented carbohydrate. Mixing again the watery
liquid in the yogurt solids helps in retaining the initial nutrition; otherwise
some protein and carbohydrate are lost along with calcium and some other
minerals
Yogurt Composition
• Water 84%
• Carbohydrates (lactose) 4.7%
• Fats 3.3%
• Proteins 8 %
• Minerals (ash) traces
17. Butter
Traditionally butter is made by churning milk cream by hands in pot; this process
separates butterfat (fats present in milk) and buttermilk(watery milk). Butter
consist of fats, little amount of milk protein and water. Most of the water is
removed as buttermilk.
Butter can also be prepared in home, collect milk for several days and preserve it
in freezer, and then churn it in electric mixer. Churning will form lumps of butter
in liquid buttermilk which is to be strained to get pure butter
Composition of Butter
• Water 16%
• Carbohydrates (lactose) 0.1%
• Fats 80%
• Proteins 0.8 %
• Minerals (ash) traces
18. Ghee (Clarified Butter)
Ghee is nothing but clarified butter, it’s made from butter or cream when
water is evaporated by heating it and milk solids set leaving above only liquid
butterfat which is called ghee and it becomes solid at room temperature
Ghee does not contain any water or milk solids like butter.
Composition of Ghee (Clarified Butter)
• Water 0.3%
• Carbohydrates (lactose) 0%
• Fats 99%
• Proteins0.04 %
• Minerals (ash) traces
19. PANEER
Milk is boiled and then coagulated with either previous day’s fermented whey
or with an acid, usually citric or lactic. Acidulate is added until clear whey
separates from the coagulum. The precipitate is collected in a muslin cloth,
hung for a few hours and then lightly pressed in order to further drain the
whey.
COMPOSITION
• Water 50-54%
• Carbohydrates (lactose) 0%
• Fats 25-27%
• Proteins 18.3%
• Minerals (ash) traces
