Early man, probably, lived much like the beasts, taking his food in a raw state. Civilized man requires much of the raw material to be changed by the action of heat into substances more palatable and already partly digested.
The chemistry of cooking the raw materials is very simple. It is in the mixing of incongruous materials in one dish or one meal that complications arise.
The cooking of starch, as rice, farina, etc., requires little explanation. The starch grains are prepared by the plant to keep during a season of cold or drought and are very close and compact; they need to be swollen and distended by moisture in order that the chemical change may take place readily. Starch grains may increase to twenty-five times their bulk by absorbing water.
The cooking of the potato and other starch-containing vegetables, although largely a physical or mechanical process is very necessary as a preparation for the chemical actions of digestion; for raw starch has been shown to require a far longer time and more digestive power than cooked starch. Change takes place slowly, even with thorough mastication, unless the starch is swollen and heated, and, in case the intestinal secretion is disturbed, the starch may not become converted at all.
Our breakfast will undoubtedly contain bread. Bread of some kind has been used by mankind from the first dawn of civilization. During the earlier stages it consisted chiefly of powdered meal and water baked in the sun or on hot stones. This kind of bread had the same characteristics as the modern sea-biscuit, crackers, and hoe cakes, as far as digestibility was concerned. It had great density; it was difficult to masticate; and the starch in it presented but little more surface to the digestive fluids than that in the hard compact grain, the seed of the plant.
Experience must have taught the semi-civilized man that a light porous loaf was more digestible than a dense one. Probably some dough was accidentally left exposed; yeast plants settled upon it from the air; fermentation set in, and the possibility of porous bread was thus suggested.
A light, spongy, crisp bread with a sweet, pleasant taste, is not only aesthetically but chemically considered the best form in which starch can be presented to the digestive organs. The porous condition is desired in order that as large a surface as possible may be presented to the action of the chemical converter, the ptyalin of the saliva, and later to other digestive ferments. There is also better aeration during the process of mastication.
Very early in the history of the human race, leavened bread seems to have been used. This was made by allowing flour and water to stand in a warm place until fermentation had well set in. A portion of this dough was used to start the process anew in fresh portions of flour and water. This kind of bread had to be made with great care, for germs different from yeast might get in, forming lactic acid - the acid of sour milk - and other substances unpleasant to the taste and harmful to the digestion.
A sponge made from perfectly pure yeast and kept pure may stand for a long time after it is ready for the oven and still show no signs of sourness.
On account of the disagreeable taste of leaven and because of the possibility that the dough might reach the stage of putrid fermentation, chemists and physicians sought for some other means of rendering the bread light and porous. The search began almost as
Leaven or Yeast soon as chemistry was worthy the name of a science, and one of the early patents bears the date 1873. Much time and thought have been devoted to the perfecting of unfermented bread; but since the process of beer-making has been universally introduced, yeast has been readily obtained, and is an effectual means of giving to the bread a porous character and a pleasant taste. Since the chemistry of the yeast fermentation has been better understood, a change of opinions has come about, and nearly all scientific and medical men now recommend fermented bread, if well baked.
The chemical reactions concerned in bread-making are similar to those in beer-making. To the flour and warmed water is added yeast, a microscopic plant, capable of causing the alcoholic fermentation. The yeast begins to act at once, but slowly; more rapidly if sugar has been added and the dough is a semi-fluid. Without the addition of sugar no change is evident to the eye for some hours, as the fermentation of starch to sugar by the diastase present gives no gaseous products. The sugar is decomposed by the yeast plant into alcohol and the gas, carbon dioxide; the latter product makes itself known by the swelling of the whole mass and the bubbles which appear on the surface.
It is the carbon dioxide, which causes the spongelike condition of the loaf by reason of the peculiar tenacity of the gluten, one of the constituents of wheat. It is a well-known fact that no other kind of grain will make so light a bread as wheat. It is the right proportion of gluten (a nitrogenous substance to be considered later) which enables the light loaf to be made of wheat flour.
The production of carbon dioxide is the end of the chemical process. The rest is purely mechanical.
The baking of the loaf has for its object to kill the ferment, to heat the starch sufficiently to render it easily soluble, to expand the carbon dioxide and drive off the alcohol, to stiffen the gluten, and to make chemical changes which shall give a pleasant flavor to the crust. The oven must be hot enough to raise the temperature of the inside of the loaf to 2120 F, or the bacteria will not all be killed. A pound loaf, four inches by four inches by nine inches long, may be baked three-quarters of an hour in an oven where the temperature is 4000 F, or for an hour and a half, when the temperature during the time does not rise above 3500 F. Quick baking gives a white loaf, because the starch has undergone but little change. The long, slow baking gives a yellow tint, with the desirable nutty flavor, and crisp crust. Different flavors in bread are supposed to be caused by the different varieties of yeast used or by bacteria, which are present in all doughs, as ordinarily prepared.
The brown coloration of the crust, which gives a peculiar flavor to the loaf, is caused by the formation of substances analogous to dextrine and caramel, due to the high heat to which the starch is subjected.
Object of Baking The Crust
One hundred pounds of flour are said to make from 126 to 150 pounds of bread. This increase of weight is due to the incorporation of water, possibly by a chemical union, as the water does not dry out of a loaf, as it does out of a sponge. The bread seems moist when first taken from the oven, and dry after standing some hours, but the weight will be found to be nearly the same. It is this probable chemical change which makes the difference, to delicate stomachs, between fresh bread and stale. A thick loaf is best when eaten after it is twenty-four hours old, although it is said to be "done" when ten hours have passed. Thin biscuit do not show the same ill effects when eaten hot.
The bread must be well baked in any case, in order that the process of fermentation may be stopped. If this be stopped and the mastication be thorough, so that the bread when swallowed is in finely divided portions instead of in a mass or ball, the digestibility of fresh and stale bread is about the same.
The expansion of water or ice into more than seventeen hundred times its volume of steam is sometimes taken advantage of in making snow-bread, water-gems, etc. It plays a part in the lightening of pastry and crackers.
Air, at 70 degrees, doubles its volume at a temperature of 560 degrees F, so that if air is entangled in a mass of dough, it gives a certain lightness when the whole is baked. This is the cause of the sponginess of cakes made with eggs. The viscous albumen or "white of egg" catches the air and holds it, even when it is expanded, unless the oven is too hot, when the sudden expansion is liable to burst the bubbles and the cake falls.