SIMPLIFICATION OF THE GERBER TEST USED FOR TESTING FAT
IN MILK
By ZAL R. KOTHAVALLA, D. R. KASHYAP AND NOSHIR N. DASTUR. Imperial Dairy Research
Institute, Bangalore
(Received for publication on 8 June 1943)
IN India the Gerber method for testing fat in
milk is almost universally used. The method
embodies accuracy with simplicity. Its only
drawback is that it cannot always be carried out
under village conditions, without an expensive
outfit. The war conditions have added to the
difficulty of obtaining the equipment at present.
According to the standard method, centrifuging is
essential. Purchase of such a costly machine is
usually beyond the means of small producers,
especially so at present. The following preli-
minary studies were, therefore, carried out with
a view to modifying the technique of the Gerber
test so that by using the same standard glassware,
the costly centrifuge might be dispensed with,
without reducing the accuracy of the results.
EXPERIMENTAL
(i) The effect of keeping test solution for different
time intervals on the Gerber test
This part of the experiment was planned with
the object of determining how long a fieldman
could safely keep the mixture of milk, acid and
alcohol in a fit condition before taking the reading,
and without in any way impairing the accuracy
of the test, in case a centrifuge was not readily
available. Reaction mixtures containing 10 ml.
of sulphuric acid (sp. gr. 1.82), 11 ml. of milk and
1 ml. of amyl alcohol were prepared and kept at
room temperature for different intervals of time
as shown in Table I. Readings were taken after
each time interval, after placing butyrometers in
a water-bath at 160°F., both with and without
centrifuging. The results for cow and buffalo
milk are shown in Table I.
These results show that when the conventional
method of making the Gerber test is followed and
the tubes dipped in a water bath at 160° F. for
five minutes before centrifuging, it is immaterial
after what interval between the mixing and
dipping of the reaction mixture the test is read.
It is also interesting to note that, by merely
keeping the butyrometers containing reaction
mixture at room temperatures for about eight
hours and then dipping them in a water bath at
160° F., correct readings can be obtained. At
shorter intervals than eight hours, the results were
not consistent.
(ii) Effect of adding amyl alcohol at a later stage
In the standard method the alcohol is added
after the milk and just before the mixture is shaken
vigorously. Trials were carried out to see what
the effect was of adding amyl alcohol after
allowing the mixture of milk and acid to stand
over different periods and just before putting the
butyrometers in the bath. In this case also the
readings were taken after each time interval,
after placing in a water bath both with and with-
out centrifuging. The results are given in Table II.
The results showed that if sufficient time is not
allowed between adding of the amyl alcohol and
putting the sample in the bath the fatty layer
does not separate quick enough to give correct
reading and centrifuging is, therefore, necessary.
(iii) Effect of temperature on the Gerber test
For taking readings in the standard Gerber test
the temperature of the reaction mixture recom-
mended is 140°-160°F. To test the effect of
temperature on the Gerber test, three tempera-
tures were tried out, viz. 120°F., 149°F. and 160°F.
TABLE I
Effect of time interval on the Gerber test
Sample
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Time
interval
in hours
2
4
6
8
24
48
72
96
120
144
168
192
216
240
Cow whole milk
Reading after
keeping in water
bath at 160°F.
5 min.
5 min
and
then
centrifu-
ging
(Initial fat test
4.3 per cent)
3.8
4.0
3.9
4.3
4.3
4.3
4.3
4.3
4.4
4.3
4.3
4.3
4.3
4.3
4.3
4.3
4.3
4.3
4.3
4.3
4.3
4.3
4.4
4.3
4.3
4.3
4.3
4.3
Buffalo whole
milk
Reading after
keeping in water
bath at 160°F.
5 min.
5 min
and
then
centrifu-
ging
(Initial fat test
6.2 per cent);
6.0
5.9
6.1
6.2
6.2
6.2
6.3
6.3
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.3
6.3
6.2
6.2
6.2
6.2
6.2
6.2
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