Experimental cookery

Fat. Butter fat is composed of glycerol and fatty acids. Fatty acids of both the saturated and unsaturated series are present. The relative per- centage of the unsaturated fatty acids varies with the feed, averaging higher in summer than in winter. Dean and Hilditch state that the oleic and linoleic acids increase by 4 per cent (mols), with a parallel diminution in butyric and stearic acids when cows return to pasture. They also report that with increased age of the cow the unsaturated acids increase at the expense of palmitic acid, which was lowered from 29 to 22-23 per cent by weight of the total fat in the four years of observations made on milk from the same group of cows. The saturated fatty acids are butyric, caproic, caprylic, capric, lauric, myristic, plamitic, and stearic. Arachadonic acid has been reported absent by some investigators. Butter fat contains a higher proportion of the first-named saturated acids than other food fats. The first ones in the series are quite volatile with steam, the volatility decreasing with increase in molecular weight of the acid. Hence, when butter is heated for several minutes, the percentage of the lower saturated fatty acids may be decreased. The unsaturated fatty acids include oleic, linoleic, and arachidic. Formerly it was thought that the particular flavor of butter was due to the greater proportion of the lower saturated fatty acids, but now it is \ 296 MILK AND CHEESE known that butters with satisfactory flavor and aroma (Michaelian, Farmer, and Hammer) contain considerable quantities of acetylmethyl- carbinol plus diacetyl. The acetylmethylcarbinol in a pure condition is odor- less, but by bacterial action it is changed to diacetyl, which in concentra- tions of 0.0002 to 0.0004 per cent in or added to neutral butter gives a characteristic aroma. Size of fat globules. The fat in milk is found in small globules. These fat globules which are microscopic in size are suspended in the milk. They vary in size from 0.10/* to 22.0/x. Most of the globules are less than lOfx and average about 3fx in diameter. The size of the fat globules varies (1) with different breeds, being larger in milk from Jersey and Guernsey than in milk from other breeds, (2) with the lactation period, decreasing in size with length of the lactation period, and (3) with feed. Dry feed tends to decrease the size of the globules, succulent feed to increase their size. Ci'eaming. The specific gravity of the fat globules is less than that of the fluid of the milk. Hence there is a tendency for them to rise to the surface to form a cream layer. The extent of creaming depends upon several factors, such as the size of the fat globules, temperature of the milk, acidity, physical state of the fat, etc. Creaming occurs more rapidly in milk when the fat globules are quite large than when they are smaller. In rising to the top of the milk the globules of fat clump together, and this clumping increases the tendency for them to rise to the surface of the milk. As the larger clumps rise they may carry many of the smaller globules to the surface. Therefore, clumping not only aids the completeness of creaming but also the rate, for the rate is more rapid when the fat particles clump quickly.