M.
A.
SAMUEL
ET.,
AL.
21
It is thus seen that heating for five minutes sufficed to reduce nearly 90 pe r cent
of the free fatty acide present and that prolongation of the heating period over 40
minutes did not yield any greater benefit.
(d) Filtering refined ghee. Studies reported so far were carried out by filtering
the refined ghee through a filter paper. It was felt that this type of filteration may not be
possible under existing trade conditions and some modification of the process was
necessary. It was found that if this mixture of lime and ghee was heated to 108°C
the lime and ghee phase separated out, giving a clear ghee layer at the bottom. When
this happened, ghee could be easily filtered through a piece of flannel or muslin. It was
further noticed that this separation was not quite clear when using 1 per cent and 2
per cent lime but with 3 per cent it was very sharp. Any temperature below 106°C.
was not effective. Ghee filtered through cloth was found to have a slight turbidity
on account of suspended calcium soaps The amount of calcium, estimated as CaO, on
three samples of refined ghee was 0.01, 0.03 and 0.03 per cent. The presence of this little
impurity did not impart any off flavour or taste to ghee. If this is considered objectionable
in any way, resort will have to be taken to a steam-heated filter press.
Very often filteration of the separated ghee at about 60°C. through ordinary blotting
paper gives a very good product.
(e) Large scale trials on refining of high acid ghee using lime. The following process is
recommended :—
(i) Ghee to be refined is heated to about 60°C. and then lime is sprinkled over
the surface at the rate of 3 per cent of the ghee which is gently stirred. Lime used
must be of as pure a grade as possible. Shell lime or dry hydratted lime is suitable ;
it is ground to a fine powder, passing through at least a 60 mesh sieve. The
temperature is quickly brought up to 108°C The fire is then put off and ghee allowed
to settle. When cooled to about 60°C., it is filtered. The results of these refining
trials are given in Table XII. It is found that the top layer of lime tends to retain
a considerable quality of ghee and it is advisable to heat it again to recover a part of
this ghee.
(ii) During refining a loss of about 6.5 per cent on the net weight of ghee occurs.
This is mainly held by lime. The cost of refining has been calculated as six annas
per lb. of ghee on net weight i.e , after subtracting the weight of free fatty acids) and
1.3 annas on the gross weight. The cost of high acid ghee has been taken as eight annas
per lb.
(iii) A record of the change in the chemical composition on refining was kept.
It was noticed that there was a slight increase in the butyrorefractometer index and
Riechert value and a decrease in the saponification value. The changes were, however,
negligible.
The refined ghee had a better colour and flavour. Preparation fried in refined ghee
did not give any soapy flavour.
Studies on the keeping quality of refined ghee have also been carried out on a few
samples. The results are given in Table XIII.
These results show that on the whole refined ghee has a much better keeping
quality than the original. There is no rapid development of free fatty acids. Usually
it is very difficult to remove rancidity from fat, once such a change has occurred.
It is, therefore, encouraging to note that the lime treatment is beneficial in this direction
also.
In the present investigation studies have been confined to the refining of high
acid ghee. In view of the results obtained it is felt that it will be quite possible to
extend the use of solid alkaline adsorbents to the removal of free fatty acids from
vegetable oils and other fats.