INVESTIGATIONS ON EVAPORATED BUFFALO MILK
By C. P. ANANTAKRISHNAN and ZAL R. KOTHAVALLA, Imperial Dairy Research Institute, Bangalore
(Received for publication on 29 October 1945)
E VAPORATED milk is condensed milk to which no extraneous sugar has been added and which
has been sterilized in hermatically sealed cans. Much attention has been paid towards the
study of the preparation and properties of the evaporated cow's milk, but very little work has been
done on the milk of other animals. In India, buffaloes form an important source of milk and dairy
products and the milk and butterfat from these animals have formed the subject of many investi-
gations. However, no information regarding the suitability of buffalo's milk for condensing seems
to be available. Therefore, investigations were carried out to get information as to (1) the possible
method of finding out the stability of evaporated milk during sterilization and (2) the applicability
of 'rapid tests' which are at present in general use (for cow's milk) for predicting the heat stability
of evaporated buffalo milk.
EXPERIMENTAL
The main factors contributing towards the success of milk condensing are uniform behaviour
of liquid milk and uniform composition. Uniform composition is important in controlling the degree
of condensing aimed at, which is generally done by determining the specific gravity. The standard
in Great Britain for evaporated milk is 9 per cent fat and 22 per cent solids-not-fat. This gives a
Fat: S.N.F. ratio of 1:2.44 which nearly conforms to the ratio for the average composition of fluid
milk and allows for a slightly lower fat content. The United States standards are lower than the
above. Previous to July 1940 the minimum standards for evaporated whole milk were 8 per cent
fat and 28 per cent total milk solids. In the present investigation the fat: solids-not-fat ratio aimed
at is 9:22. In order to obtain this ratio in the raw milk and to facilitate the control of the degree
of concentration reached later, the liquid milk is toned to 4.0 per cent fat always, unless otherwise
stated. The milk used in all cases was a composite sample from the Murrah buffalo herd of the
Institute farm.
Milk was always taken for condensing four hours after production. Condensing was done in
a pilot condensing unit manufactured by The Dairy Engineers Ltd., Edinburgh. Forewarming
was effected by steam in a tinned copper kettle with revolving agitator, evaporation in a tinned
copper vacuum pan, and condensation in a surface condenser. The vacuum is created by means of
a wet vacuum pump.
VACUUM PAN OPERATION
The vacuum pan was thoroughly rinsed with water and steamed for 10 minutes. The air valves
were closed, and water turned into the condenser. Then water was allowed into the vacuum pump
and the pump was started. When the vacuum gauge registered over 62 cm. the valve of the milk
pipe leading to the pan was closed. When the milk just filled the jacket and when it touched the
steam coil in the pan, steam was turned into it. When all the milk was drawn into the pan the
inlet was closed and the steam pressure in the jacket was increased gradually and taken up to 22 lb.
in about 6 minutes. The temperature of the vacuum pan was maintained between 122 to 128°F.
If the inside temperature of the pan was increased more than 128°F. initially, milk would begin to
froth too much and might even be carried on to the condenser. Therefore, the steam pressure in
the jacket should be carefully controlled. It has been found by various trials that a steam pressure
of 22 lb. in the coils was quite suitable for condensing the milk. The temperature of the outlet
water from the condenser ranged from 110 to 115°F. Just before the desired concentration was
reached (judged by looking through the man-hole) a sample was drawn out from the pan and its
specific gravity determined at a temperature of 110°F. When the specific gravity was about 1.066,
the steam pressure in the jacket and the coils was reduced, the vacuum break opened, the vacuum
pump and the steam in the jacket were stopped. The condensed milk is then drawn out of the pan
and cooled to room temperature 72.76°F.
After standardization to the desired composition, the evaporated milk was filled in 8 oz. sterile
vent hole cans, or in sterile glass bottles plugged with cotton wool and used for sterilization studies.
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