Good wheat flour ought to be white, not gritty or lumpy, not acid or musty, forming a coherent stringy dough. Examined microscopically, it should show the absence of any fungi, or acarus farinæ, or of foreign starches, such as barley, maize, rice, potato, known by the different shape of their starch granules. (See Fig. 1.) Alum has been occasionally added to flour, to enable the baker to make a white and porous bread from damaged wheat flour. It can be detected as follows:—Pour over the freshly cut surface of a slice of bread some freshly prepared decoction of logwood chips, and then a solution of carbonate of ammonia. If alum is present, the bread turns a marked blue to violet colour; but if the bread is pure, it is only stained pink.
The wheat grain may be used as food in its entirety. Thus boiled in milk, after having been soaked in water, it forms the chief constituent of frumenty. Usually it is converted into flour by grinding or milling. A grain of wheat consists of three parts, an outer envelope, the bran, consisting chiefly of indigestible cellulose, and composing 13½ per cent. of the grain; the kernel, or endosperm, which makes up 85 per cent. of the grain; and the germ, forming 1½ per cent. of the grain. In the old method of stone grinding, the bran was removed, and the germ left along with the endosperm. In the elaborate processes of modern roller milling, the bran is removed as in the old grinding, because it cannot without the greatest difficulty be reduced to powder; and the germ is also removed, because the oil abundantly present in it is apt to become rancid and spoil the flour, and because the soluble proteids in it are apt to change some of the flour into dextrin and sugar, which become brown in baking and spoil the appearance of the bread. The germ is easily removed, because its toughness causes it to be flattened out in the milling, while the endosperm becomes powdery. The central part of the endosperm is the source of ‘patents.’ It is very rich in starch and is used for making fancy breads and pastry. The outer part of the endosperm is ‘households.’ ‘Households flour’ is subdivided into (a) second patents, or ‘whites’; (b) first households; (c) second households or ‘seconds.’ ‘Seconds’ is richest in gluten, ‘whites’ in starch. Ordinary bread is normally derived from a blend of these three. Some ‘strong’ wheats, e.g. Australian, yield a ‘patents’ which is rich in gluten, and such flour is used for making Vienna bread. ‘Strong’ wheats take up most water in baking, and so yield most loaves per sack. ‘Seconds’ flour yields a bread which is richer in proteid than most other kinds; but the dark colour of the loaf makes it unpopular. Various schemes have been devised to utilise the germ and the bran, which are ordinarily discarded. In the preparation of Hovis flour the separated germ is partially cooked by superheated steam. This kills the ferment contained in the soluble proteids, and thus prevents it from changing starch into maltose and dextrin. The action thus prevented is represented by the following formula:—
STARCH.MALTOSE.DEXTRIN.
10 C12H20O10 + 6 H₂0 = 6 C12H22O11 + 4 C12H20O10.
The germ thus treated is ground to a fine meal, of which one part to three of ordinary flour, forms Hovis flour. Other ‘germ breads’ are also in the market. In the making of Frame food the bran is boiled with water under high pressure. The watery extract, containing the mineral and part of the nitrogenous constituents of the bran, is evaporated to dryness, and forms the basis of various preparations. It is doubtful if this food possesses any great value.
Brown bread is a somewhat vague expression, meaning either an admixture of bran or of germ or of both with flour, or bread made from whole wheat flour. In each of these cases the loaf would be brown. The bran is rich in fat as well as in phosphates. It acts as a mechanical irritant, ill borne by delicate stomachs, but very useful where a tendency to constipation exists. The excess of nitrogenous matter in brown bread and its richness in fat, do not prove its greater nutritiveness, as it is present in a condition in which only a portion is absorbable from the alimentary canal into the circulation.
The harder wheats, such as Sicilian wheat, contain a larger percentage of gluten; and from them macaroni and vermicelli are obtained, which are nearly pure gluten. They are very nutritious and useful foods. Semolina is prepared from wheat, the millstones being left sufficiently apart to leave the product in a granular condition. In malted breads, a syrupy infusion of malted barley (malt extract) is added to the flour. Malt extract contains in addition to malt sugar (maltose) and dextrins, a ferment (diastase) which, like the saliva, is able to convert starch into the soluble substances, maltose and dextrin (see formulæ above). The action of this ferment is stopped by the temperature of baking. Hence even when the malt extract is allowed a considerable time for its operation on the dough, only about 10 per cent. of the starch in the loaf becomes soluble, as compared with 4 per cent. in an ordinary loaf.
Oatmeal, obtained from the common oat, contains very little gluten, and so cannot be made into vesiculated bread. It contains a large proportion of other nitrogenous material and of fat. As porridge and oatmeal cake it forms a very nutritious diet. The husk ought to be carefully removed from the meal intended for human food, as, although very nitrogenous, it acts as a mechanical irritant. Groats consists of oats from which the husk has been entirely removed. The substitution of rolling for grinding in preparing oats for food and the application of heat during the rolling process, have made oatmeal more digestible, as in Quaker, Provost, and Waverley oats.
Barley contains very little gluten; on this account, like oatmeal, it does not admit of being made easily into bread.
Malt is barley which has been made to germinate by heat and moisture and then dried, “diastase” being formed in the process. Extract of malt, containing diastase in an active condition, is useful in cases of impaired digestion and deficient assimilation of food.
Rye is rarely used in this country for making bread. In Germany it is known as “black bread,” but its colour and acid taste make it disagreeable, and it is laxative in its action.