The temperature at which a fat becomes hard is a fair guide to its digestibility. Thus we know that beef, and still more, mutton fat, would become solid, under conditions in which bacon dripping is still soft. Where digestion is weak, there may be an instinctive loathing of fat meat; for such persons, especially for children, some other fat should always be substituted. Thus the addition of butter to the potatoes makes up the deficiency.
Butter forms 3½ to 4½ per cent. of cow’s milk. It is separated from milk by churning, the oil particles being deprived by this means of their albuminous coats. The more completely the butter-milk is separated the longer the butter keeps. It can be kept longer if salt is added, or in hot weather by keeping it under frequently-changed water. Rancidity indicates the decomposition of traces of the fat of butter into its fatty acid and glycerine.
Cream contains about 30 per cent. of butter fat, Cheshire cheese 25 per cent., and skim milk cheese 7 per cent.
Butter milk differs from skim milk in the presence of lactic acid. It is more digestible than skim milk, the casein being in a more flocculent condition.
The odour and flavour of butter are not due to olein and palmitin, the two chief constituents, but to a smaller quantity of butyrin, caproin, and caprylin fats of a much lower series. Ordinary butter contains a considerable proportion of water, and the presence of about 8 per cent. renders it more palatable; if it is over 15 per cent., the butter is considered adulterated. An excessive amount of salt is sometimes present. The most frequent adulteration is the substitution of foreign fats for butter fat, e.g. lard, palm oil, rape seed oil, or cocoa-nut oil. Margarine is most frequently used for this purpose.
Margarine is prepared from beef-fat by melting, the stearin becoming solid again at a temperature at which olein and margarine still remain liquid. It forms a wholesome and cheap food, being nearly as digestible as butter, for which more expensive food it is often fraudulently sold. When mixed with a small proportion of butter its recognition by smell, etc., is almost impossible, but on careful chemical analysis, it is found to have a higher melting point and a lower specific gravity than butter, and a much smaller percentage of soluble fatty acids than the latter. Thus:—
| MELTING POINT. | SPECIFIC GRAVITY. | SAPONIFICATION AND FORMATION OF INSOLUBLE FATTY ACID. | |
|---|---|---|---|
| Butter | 32° C. | .913 | 88 per cent. insoluble fatty acid |
| Margarine | 35° C.[1] | .904-.907 | 95[2] per cent. insoluble fatty acid |
Cereal Foods.—Gluten is peculiar to plants, and is chiefly found in plants belonging to the great family of grasses. Gluten is to bread what casein is to milk, and myosin to flesh. If one takes a piece of dough made from wheat flour, and holds it under a stream of water from the tap, a large part of it is washed away, while a sticky adherent mass is left behind. This is gluten, and it is its tenacity which enables bread to be made. If the fluid with which the dough was washed is collected, it will be found to contain a large quantity of starch, a small amount of sugar, of albumin, and certain salts. All cereals possess these constituents in various proportions, as may be seen from the following table:—
| WATER. | PROTEID. | FAT. | CARBO- HYDRATES. | CELLULOSE. | MINERAL MATTER. | |
|---|---|---|---|---|---|---|
| Wheatmeal | 12.1 | 12.9 | 1.9 | 70.3 | 1.6 | 1.2 |
| Fine wheat flour | 13.0 | 9.5 | 0.8 | 75.3 | 0.7 | 0.7 |
| Oatmeal | 7.2 | 14.2 | 7.3 | 65.9 | 3.5 | 1.9 |
| Barley meal | 11.9 | 10.0 | 2.2 | 71.5 | 1.8 | 2.6 |
| Maize meal | 11.4 | 8.5 | 4.6 | 72.8 | 1.4 | 1.3 |
| Rice (husk removed) | 12.0 | 7.2 | 2.0 | 76.8 | 1.0 | 1.0 |
The proteid varies in character in the different cereals; wheat flour has the largest proportion of gluten (8 to 12 per cent.) and therefore makes the best bread.