C. P. ANANTAKRISHNAN AND ZAL R. KOTHAVALLA 107
In general it can be concluded from Table I that as the concentration of the milk solid increases
the temperature of coagulation for 30 minute sterilization decreases progressively, but there was
no definite relationship between concentration and the change of coagulation temperature. A 22
per cent S.N.F. sample could be sterilized without coagulation between 237.2 to 244.4°F. for 30
minutes, but a few samples of 22 per cent S.N.F. which were not recorded in the table, coagulated
even at 233.6°F.
Effect of various temperatures of sterilization on the time of coagulation of evaporated milk
Buffalo milk toned to 4 per cent fat was forewarmed at 203°F. for 5 minutes and condensed
to 22 per cent S.N.F. The product was transferred to glass bottles and sterilized for various lengths
of time at 233.6, 237.2, 240.8, 244.4, and 248.0°F. Four samples were tried at each temperature
and the results are presented in Table II.
TABLE II
Time temperature relationship in the sterilization of evaporated buffalo milk
Sterilization temperature °F
248.0
244.4
240.8
237.2
233.6
Time of coagulation in minutes
Sample No.
1
15
30
25
35
40
2
10
15
30
35
40
3
15
15
20
40
25
4
15
25
25
35
35
Average
13.8
18.8
25.0
35.0
35.0
It can be seen from Table II that as the temperature of sterilization decreases the time required
for coagulation increases for the product having 22 per cent S.N.F. The average time of coagula-
tion for an evaporated milk of 22 per cent S.N.F. at 240.8°F. is about 25 minutes. The acidity of
the samples of milk used in the above experiments ranged between 0.12 to 0.14 per cent. Six samples
having 0.15 per cent acidity were found to coagulate at 233.6°F. in 25 minutes.
Effect of temperature of forewarming on the time of coagulation of the evaporated milk
The temperature and the time of forewarming of milk are known to have considerable effect
on the heat coagulation of evaporated milk. Webb and Holm [1932] have shown that the concen-
tration of S.N.F. is important in determining the effect of temperature and time of heating on heat
coagulation. They conclude that forewarming at high temperatures lowers the stability of samples
with high concentrations of S.N.F. It is also known that heating a milk to boiling prior to its eva-
poration strikingly increases the heat stability of its evaporated product. With a view to study
the effect of forewarming on the stability of buffalo milk, various forewarming temperatures were
tried. Buffalo milk toned to 4.0 per cent fat was forewarmed to 105, 185, and 203°F. respectively
for five minutes and evaporated to 22.0 per cent S.N.F. and the time of coagulation at 240.8°F. was
noted. Four samples were used at each forewarming temperature. The results of these experi-
ments arel presented in Table III.
Table III shows that, as the temperature of forewarming increases, the time of coagulation
at 240.8°F. increases. All the four samples which were not forewarmed at all curdled at 240.8°F.
in less than five minutes. Forewarming definitely increases the heat stability of the evaporated
buffalo milk and heating at 203°F. for five minutes is comparatively better than lower temperatures
of forewarming. There is no marked physical thickening of the product prepared from milk fore-
warmed at 203°F. for five minutes, on storage for about three months. It was also of interest to
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