C.
P.
ANANTAKRISHNAN
AND
ZAL
R.
KOTHAVALLA
109
and phosphate tests were carried out on milk samples before forewarming and condensing. Milk
was considered alcohol positive when a precipitate appears with equal parts (2 ml.) of milk and 74
per cent alcohol. The ± point was taken as positive to 74 per cent alcohol and negative to 68 per
cent alcohol. When negative to 68 per cent alcohol the milk was considered alcohol negative. The
method of Ramsdell et al [1931] was adopted for the phosphate test. Ten ml. of milk sample were
taken in a test tube of approximately 20 ml. capacity and one ml. of phosphate solution (68.1 gm.
of mono basic potassium phosphate in one litre of water) was added to it. The contents of the tube
were then mixed and the tubes immersed in a boiling water bath for 5 minutes. The tubes were
then removed, cooled and the mixture examined for the presence of curd. Any visible coagulation
indicated that the concentrated product would be of a low heat stability. Twenty-five trials were
conducted with farm produced milk having acidity ranging from 0.12 and 0.15 per cent and the results
are presented in Table V.
TABLE V
Relation of alcohol and phosphate test with the time of coagulation of evaporated buffalo milk
Number of trials
8
7
4
3
3
Alcohol
test
—
—
+
+
+
Phosphate
test
—
+
+
—
—
Coagulation
time at
240.8° F. in
minutes
23
20
16
22
14
From the above table it is seen that when the alcohol test is negative or + the coagulation time
ranges between 20 and 23 minutes. Eighteen samples out of 25 gave an indication from the alcohol
test that they are fairly heat stable. Seven samples which gave positive alcohol tests coagulated
within 16 minutes. Therefore, there is some relation between the alcohol test and heat stability
of the evaporated product. Fourteen samples which gave negative phosphate tests coagulated
at a temperature ranging from 14 to 23 minutes, while seven others which gave positive phosphate
tests were fairly heat stable and four others which gave positive phosphate tests were not heat stable.
Therefore, comparatively, the alcohol test appears to be more reliable in predicting the heat stability
of the evaporated buffalo milk.
The effect of added salts on the heat coagulation of evaporated milk
The temperature at which evaporated milk curdles during sterilization is greatly affected and
to a large extent controlled by the balance of milk salts. This fact is known in a general way but
it remains to be investigated how added salts affect the heat stability of evaporated buffalo milk.
Milk with 4.0 per cent fat was forewarmed at 203°F. for 5 minutes and condensed to 22.0 per cent
S.N.F. In each of the 6 sterile bottles 140 gm. of the evaporated milk were taken, and one of the
bottles was used as a control. To the others 0.2, 0.4, 0.6, 0.8 and 1.0 ml. of di-sodium phosphate
solution (8.4 per cent strength) were added and well mixed. Wherever necessary the samples
were adjusted for dilution by means of distilled water. All the samples were sterilized at 240.8°F.
for 30 minutes. Similarly, the effect of sodium citrate of various concentrations on the heat coagula-
tion of evaporated milk were also studied. Thus the effect of both these salts on the heat stability
of evaporated milk was independently investigated. Twelve samples were tried and the results are
presented in Table VI.