1921.] Wright.—Chemical Technology of Meat Industry. 
99 
a stronger odour and flavour than fats rendered at comparatively low 
temperatures ; the fats are thus practically unfit for edible purposes. 
The contents of the digester after cooking are allowed to settle, when 
it will be found that the clear fat as a hot liquid is floating upon the 
surface of an aqueous gluey fluid, while the membranous matter and 
residual hash of animal-tissue and bones will be at the bottom of the vat. 
The fat, after the contents of the digester have settled, is drawn off by 
any suitable means. The methods of doing this vary and may involve 
drawing off through side cocks, “ floating off,” or “ blowing off ” ; but, 
whichever method is employed, the fat is run into refiners in which any 
residual moisture and membranous matter are removed. 
The process of refining is essentially a method of settling out the 
impurities by heating the fat with steam, whereby the moisture, which 
may be in emulsion in the fat, coalesces to form larger drops of water, 
which can then readily fall to the bottom of the refining-tank. The 
settling of the impurities is aided by sprinkling over the surface of the 
hot liquid fat a quantity of salt, which in falling through the liquid fat 
mechanically carries with it the impurities. 
From the refiner, after thorough settling, the fat is run into coolers 
with mechanical stirrers, and thence into casks, the material in the casks 
being stirred until semi-solid. The reason for maintaining the agitation 
of the fat until nearly solid is to prevent granulation or “ seeding ” of the 
fat. The “ seeding ” of fat is really the crystallization-out of the harder 
glycerides ; and, while “ seeding ” is regarded as desirable in an edible 
fat, it is looked upon with disfavour in a tallow. Why this should be is 
not clear ; in the case of an edible fat which is subsequently pressed in 
order to obtain the oleo oil for margarine it is apparent that the crystalli¬ 
zation-out of the harder stearines is desirable, but an inedible tallow which 
is used for soap and other industrial purposes requires to be remelted as 
a whole, hence its crystallization at the time of manufacture cannot be a 
factor of real moment. 
After the fat is removed from the digesters the residual gluey liquor 
is run into settling-tanks and catch-basins to retain the fat still in the 
liquid, which is subsequently evaporated down to recover the solid consti¬ 
tuents in solution ; and the fat recovered from the catch-basins is refined 
in the usual manner and casked as tallow. The membranous tissue, meat¬ 
like hash, and bones are drawn off from the bottom of the digesters and 
pressed, and the liquid, from the pressed material is likewise run through 
catch-basins to recover the fat, which is refined as tallow. The treatment 
of the pressed sludge and the liquor from the digesters will be considered 
under separate headings. The oil recovered from the rendering of the 
shanks and feet is refined as neat’s-foot oil, being subsequently filtered before 
being filled into casks or drums. 
The market value of a tallow depends chiefly upon the titre and the 
colour ; but more recently the amounts of free fatty acidity, of moisture, 
and of detritus have been regarded as controlling factors as well. The 
titre, so called, is in reality the temperature (centigrade) at which the 
fatty acids of the tallow solidify, and is thus a measure of the hardness 
of the fat. It is not practicable to enter into a discussion upon the 
technicalities surrounding the titre test, but it may be stated that for 
practical purposes tallows can be looked upon as consisting in the main 
of mixtures in varying proportions of different compounds of glycerine with 
