Milk cream is a fat rich component and has been known from time immemorial as the fatty layer that rises to the top portion of the milk when left undisturbed. ‘Cream may be defined as that portion of milk which is rich in milk fat or that portion of milk into which fat has been gathered and which contains a large portion of milk fat, or when milk fat is concentrated into a fraction of the original milk, that portion is known as cream’.
In India, as per 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. Cream is rich in energy giving fat and fat-soluble vitamins A, D, E, and K, the contents of which depends on the fat level in cream.
Composition of cream
||45.45 - 68.2%
||25 - 60%
||1.69 - 2.54%
||2.47 - 3.71%
||0.37 - 0.56%
|Solids not fat
||4.55 - 6.80%
How to prepare milk cream?
I. Gravity method
When the milk is allowed to stand undisturbed for some time, there is a tendency for the fat to rise to the top due to difference in the specific gravity of fat and the rest of the components. But the gravity method being very slow, no longer commercially used for the separation of cream.
II. Centrifugal method
Centrifugal cream separators are similar to milk clarifiers in that they consist of a stack of conical discs housed in a separator bowl and rotated at high speed by an electric motor. The separator is a unit, which removes most of the milk fat from milk by centrifugal force. Its principal components are power source, a separator bowl, a set of gears and shafts, a product inlet and a product outlet for cream and skim milk. The separator bowl consists of an outer shell within which are a large number of cone shaped discs constructed so that between each pair is a very small space of not more than 0.5 mm.
As the milk enters the bowl, it is distributed into these spaces between the discs; it is immediately subjected to a tremendous force. While both the fat and skim milk are subjected to the centrifugal force, the difference in specific gravity affects the heavier portion (skim milk) more intensely than the lighter portion (i.e. cream) thereby the skim milk is forced to the periphery while the fat portion moves towards the center of axis. The skim milk and cream both form vertical walls within the bowl and are separated by being led trough separate outlets.
Any insoluble particles in the milk, such as bits of curd or dirt etc., collect as ‘separator slime’ and are thrown outward as the bowl operates and pass along with the skim milk into the space between the outer edge of the discs and the inner space of the bowl shell. Such material is deposited on this space of the bowl shell, which is removed later. Separator bowl operates at speeds as great as 20,000 rpm. The separator is a precision instrument and hence has to be in good condition and operated properly to get maximum skimming efficiency.
Characteristics of gravity and centrifugal cream methods
|Nature of force causing separation
|Speed of separation
|Direction of movement of fat and skim milk particles
|Bacteriological quality of cream and skim milk
|Fat percentage of cream
||0 to 25
||18 to 85 (can be controlled)
|Fat percentage of skim milk
||0.2 or above
||0.1 or less
|Scale of operation
|Fat percentage recovered in cream
||Not more than 90
Uses of MILK Cream
The cream can be used for direct consumption in the form of table or whipping or coffee cream. It can be incorporated in the production of special dishes. Its utility in the production of plastic, frozen and sour cream is noteworthy. Cream acts as a raw material in the production of butter, ice cream, butter oil and ghee, an indigenous dairy product. Cream also finds a place in the creaming of cottage cheese.