M. R. SRINIVASAN AND B. N.
BANERJEE
73
meet the needs of a primitive village producer. We were, therefore, left with the problem of
finding out the temperature and time of boiling of milk that would suit Indian conditions.
Milk was heated to boiling in the villager's vessel (curd pot) and the bacterial count was noted
as also the quality of the resultant curd and ghee.
Experimental. Processing of milk by boiling was tried in the following way : heating
milk to boiling point and continuing boiling for five and ten minutes as also boiling of milk
till the volume was reduced by 5 and 10 per cent. Villagers can judge the temperature from
ebullition time by counting from 1 to 100 for a minute, and evaporation loss from reduction
in volume.
Fresh buffalo milk from a nearby dairy was used for the experiments. Its acidity, fat
and lactose contents were determined. Its bacterial content as determined by plating method
was found to be 1,20,000 per c. c. The milk was then boiled (96°C. at 3,000 ft. above sea
level) in an open aluminium vessel for five and ten minutes, cooled and plated for bacterial
count. In another trial, 4.4 litres and 4.2 litres of fresh buffalo milk (bacterial count, 1,25,000)
were heated to boiling and maintained at that temperature till the volume was reduced
to 4 litres. The reduction in bacterial count in each case is recorded in Table I.
TABLE I
Variation of bacterial count with processing
Raw milk
count per c. C.
1,20,000
1,50,000
1,50,000
Count per c. c. after processing by
5 minutes
boiling
5,000
3,000
4,000
10 minutes
boiling
30
30
100
5 per cent
evaporation
—
23
30
10 per cent
evaporation
20
23
30
Steaming for
one hour
—
20
100
Four litres of milk after being processed in the aforesaid ways were poured into 2-litre
sterilized flasks up to a litre and plugged with cotton-wool. When the milk in the flasks had
cooled down to room temperature, it was seeded with a 2.5 per cent by volume of seed culture
propagated in the laboratory. The flasks were incubated at 24°, 40° and 45°C. After souring
for 6, 12, 24 and 48 hours, a flask from each set was taken out and its curd examined for
texture, flavour, acidity and lactose content. Butter was prepared in a bottle churn from the
curd and melted into ghee by the decantation method. Its colour, flavour, texture and acidity
were determined. The vitamin A content of the 48 hours soured samples at 45°C. were
determined. The induction period of the 6 and 48 hour samples at 95°C. were determined for
comparison. For the sake of control, buffalo milk was sterilized in a moist steam sterilizer
in glass flasks for 60 minutes. After sterilization the milk was cooled, seeded and analysed as
before after souring for 6, 12, 18, 24 and 48 hours at temperatures of 24°, 30°, 35°, 40° and
45°C. The results are given in Table II.
TABLE II
Processing of milk and properties of ghee
Time of incuba-
tion hours
30°C
6
12
18
24
48
Curd
Lactose
Acidity
Butter
acidity
Ghee acidity
Boiling
process
Steamed for 60 minutes
Milk—lactose 5.4, acidity 0.13 and fat 6.8 per cent
4.7
4.2
4.1
3.1
2.9
0.77
1.3
1.4
1.4
1.5
0.12
0.16
0.18
0.20
0.22
0.04
0.06
0.06
0.08
0.08
Decantation
process
0.01
0.03
0.03
0.03
0.03
Yield
91
91
92
92
90