A similar separation is what I suppose to occur in the cooking of animal fat. I find that mutton-fat, beef-fat, or other fat when raw, is perfectly smooth, as tested by rubbing a small quantity, free from membrane, between the finger and thumb, or by a still more delicate test of rubbing it between the tip of the tongue and the palate. But dripping, whether of beef, or mutton, or poultry, is granular, as anybody who has ever eaten bread and dripping knows well enough, and the manufacturers of "butterine," or "bosch," know too well, as the destruction or prevention of this granulation is one of the difficulties of their art.
My theory of the cookery of fat is simply that heat, when continued long enough, or raised sufficiently high, effects an incipient dissociation of the fatty acids from the glycerine, and thus assists the digestive organs by presenting the base and the acids in a condition better fitted (or advanced by one stage) for the new combinations demanded by assimilation. Some physiologists have lately asserted that the fat of our food is not assimilated at all not laid down again as fat, but is used directly as fuel for the maintenance of animal heat. If this is correct, the advantage of the preliminary dissociation is more decided, for the combustible portion of the fat is its fatty acids; the glycerine is an impediment to combustion, so much so that the modern candle-maker removes it, and thereby greatly improves the combustibility of his candles.
It may be that the glycerine of the fat we eat is assimilated like sugar, while the fatty acids act directly as fuel. This view may reconcile some of the conflicting facts (such as the existence of fat in the carnivora) that stand in the way of the theory of the uses of fat food above referred to, according to which fat is not fattening, and those who would "Bant" should eat fat freely to maintain animal heat, while very abstemious in the consumption of sugar and farinaceous food.
The difference between tallow and dripping is instructive. Their origin is the same; both are melted fats—beef or mutton fats—and both contain the same fatty acids and glycerine, but there is a visible and tangible difference in their molecular condition. Tallow is smooth and homogeneous, dripping decidedly granular.
I attribute this difference to the fact that, in rendering tallow, the heat is maintained no longer than is necessary to effect the fusion; while, in the ordinary production of dripping, the fat is exposed in the dripping-pan to a long continuance of heat, besides being highly heated when used in basting. Therefore the dissociation is carried further in the case of the dripping, and the result becomes sensible. I have observed that home-rendered lard, that obtained in English farm-houses, where the "scratchings" (i.e., the membranous parts) are frizzled, is more granular than the lard we now obtain in such abundance from Chicago and other wholesale hog-regions. I have not witnessed the lard-rendering at Chicago, but have little doubt that