82 The N.Z. Journal of Science and Technology. [April 
settling-out of the tissues and water, which collect at the bottom of the 
pan. 
The clear fat is then run into another series of kettles, more salt is 
sprinkled over the liquid, while the temperature is maintained at a some¬ 
what lower degree. A further settling completes the separation of tissue 
and moisture. 
The fat, which should now be free from connective tissue, membranes, 
and water, is then run into settling-boxes, and allowed to stand at a 
temperature which experience has shown to be best suited for allowing 
a crystallization of the stearin to take place, a process usually known as 
“ seeding.” The suitable temperature for “ seeding ” depends upon the 
proportion of stearin to olein, and varies somewhat .for different fats. 
After crystallization has taken place the fats are run into casks for 
shipment or other disposal. 
For success in manufacturing edible fats it is absolutely essential that 
the fat be obtained from the animal as soon after death as possible. 
The fats vary in consistency according to the food, sex, and part of the 
body from which they are obtained. Mutton is normally harder than beef. 
Mutton possesses a more pronounced odour than beef, and its flavour is 
less agreeable. 
When freshly rendered, animal-fat§ from recently slaughtered animals 
contain but very small amounts of free fatty acids. This fact was formerly 
regarded as being of considerable importance in judging the degree of 
rancidity of edible fats, and the quantity of free fatty acids present in a 
fat or oil was looked upon as a test of its freshness or rancidity. Old and 
rancid fats were found to have very high acid values. 
Rancidity, however, is now found to be due not entirely, or even chiefly, 
to the presence of the free fatty acids. It appears to be caused by the 
further action of air and moisture on the fatty acids, and also upon the 
glycerine set free when a fat is decomposed. Amongst the secondary 
products are the volatile fatty acids and certain aldehydes, especially 
oenanthaldehyde. 
In regard to edible fats, a consideration of the effects which light, air, 
and moisture exert upon the chemical composition is important. 
The effect of light alone upon a dry fat protected from the air is that 
of bleaching, oils and fats acquiring a paler colour, some even becoming 
colourless. It seems to be definitely established that light alone is unable 
to produce rancidity in oils and fats. 
The action of air, to the. exclusion of moisture and light, has no 
apparent effect at ordinary temperatures. Fats and oils will therefore 
remain practically unchanged for an indefinite time if kept protected from 
light and moisture. Since it is difficult to exclude every trace of moisture 
from fats and oils rendered under commercial conditions, it seems desirable 
to consider in some detail the effects of moisture upon oils and fats. 
The effect of moisture upon a fat is, generally speaking, to produce a 
greater or less degree of rancidity. 
Apart from the chemical changes brought about in the composition of 
fats when subjected to the action of high temperatures in the presence of 
moisture, or through the agency of strong acids or alkalis, it is important 
to note that even at ordinary temperatures changes may be brought about 
by the action of water if naturally occurring ferments or enzymes such as 
steapsin or lipase are present. In animal-fats rendered under commercial 
conditions, especially if care be not exercised in the separation of the animal- 
tissues, it will be found that a ferment similar to " catalase ” is present. 
