Читать книгу A Handbook of Health - Woods Hutchinson - Страница 23

Sources of Starch. The starches are valuable and wholesome foods. They form the largest part, both in bulk and in fuel value, of our diet, and have done so ever since man learned how to cultivate the soil and grow crops of grain. The reason is clear: One acre of good land will grow from ten to fifteen times the amount of food in the form of starch in grains or roots, as of meat in the shape of cattle or sheep. Consequently, starch is far cheaper, and this is its great advantage.

Our chief supply of starch is obtained from the seed of certain most useful grasses, which we call wheat, oats, barley, rye, rice, and corn, and from the so-called "roots" of the potato. Potatoes are really underground buds packed with starch, and their proper name is tubers.

Starch, when pure or extracted, is a soft, white powder, which you have often seen as cornstarch, or laundry starch. As found in grains, it is mixed with a certain amount of vegetable fibre, covered with husks, or skin, and has the little germ or budlet of the coming plant inside it. It has been manufactured and laid down by little cells inside their own bodies, which make up the grains; so that each particular grain of starch is surrounded by a delicate husk—the wall of the cell that made it. This means that grains and other starch foods have to be prepared for eating by grinding and cooking. The grinding crushes the grains into a powder so that the starch can be sifted out from the husks and coating of the grain, and the fibres which hold it together; and the cooking causes the tiny starch grain to swell and burst the cell wall, or bag, which surrounds it.

Starches as Fuel. The starches contain no nitrogen except a mere trace in the framework of the grains or roots they grow in. They burn very clean; that is, almost the whole of them is turned into carbon dioxid gas and water.[7]

This burning quality makes the starches a capital fuel both in the body and out of it. You may have heard of how settlers out on the prairies, who were a long way from a railroad and had no wood or coal, but plenty of corn, would fill their coal scuttles with corn and burn that in their stoves; and a very bright, hot fire it made.

One of the chief weaknesses of the starches is that they burn up too fast, so that you get hungry again much more quickly after a meal made entirely upon starchy foods, like bread, crackers, potatoes, or rice, than you do after one which has contained some meat, particularly fat, which burns and digests more slowly.

How Starch is Changed into Sugar. As we learned in chapter II, the starches can be digested only after they are turned into sugars in the body. If you put salt with sugar or starch, although it will mix perfectly and give its taste to the mixture, neither the salt nor the starch nor the sugar will have changed at all, but will remain exactly as it was in the first place, except for being mixed with the other substances. But if you were to pour water containing an acid over the starch, and then boil it for a little time, your starch would entirely disappear, and something quite different take its place. This, when you tasted it, you would find was sweet; and, when the water was boiled off, it would turn out to be a sugar called glucose. Again, if you should pour a strong acid over sawdust, it would "char" it, or change it into another substance, carbon. In both of these cases—that of the starch and of the sawdust—what we call a chemical change would have taken place between the acid and the starch, and between the strong acid and the sawdust.

If we looked into the matter more closely, we should find that what has happened is that the starch and the sawdust have changed into quite different substances. Starches are insoluble in water; that is, although they can be softened and changed into a jelly-like substance, they cannot be completely melted, or dissolved, like salt or sugar. Sugar, on the other hand, is a perfectly soluble or "meltable" substance, and can soak or penetrate through any membrane or substance in the body. Therefore all the starches which we eat—bread, biscuit, potato, etc.—have to be acted upon by the ferments of our saliva and our pancreatic juice, and turned into sugar, called glucose, which can be easily poured into the blood and carried wherever it is needed, all over the body. Thus we see what a close relation there is between starch and sugar, and why the group we are studying is sometimes called the starch-sugars.

Wheat—our Most Valuable Starch Food. The principal forms in which starch comes upon our tables are meals and flours, and the various breads, cakes, mushes, and puddings made out of these. Far the most valuable and important of all is wheat flour, because this grain contains, as we have seen, not only starch, but a considerable amount of vegetable "meat," or gluten, which is easily digested in the stomach. This gluten, however, carries with it one disadvantage—its stickiness, or gumminess. The dough or paste made by mixing wheat flour with water is heavy and wet, or, as we say, "soggy," as compared with that made by mixing oatmeal or corn meal or rice flour with water. If it is baked in this form, it makes a well-flavored, but rather tough, leathery sort of crust; so those races that use no leavening, or rising-stuff, in their wheat bread, roll it out into very thin sheets and bake it on griddles or hot stones.

Most races that have wheat, however, have hit upon a plan for overcoming this heaviness and sogginess, and that is the rather ingenious one of mixing some substance in the dough which will give off bubbles of a gas, carbon dioxid, and cause it to puff up and become spongy and light, or, as we say, "full of air." This is what gives bread its well-known spongy or porous texture; but the tiny cells and holes in it are filled, not with air, but with carbon dioxid gas.

Making Bread with Yeast. There are several ways of lightening bread with carbon dioxid gas. The oldest and commonest is by mixing in with the flour and water a small amount of the frothy mass made by a germ, or microbe, known as yeast or the yeast plant. Then the dough is set away in a warm place "to rise," which means that the busy little yeast cells, eagerly attacking the rich supply of starchy food spread before them, and encouraged by the heat and moisture, multiply by millions and billions, and in the process of growing and multiplying, give off, like all other living cells, the gas, carbon dioxid. This bubbles and spreads all through the mass, the dough begins to rise, and finally swells right above the pan or crock in which it was set. If it is allowed to stand and rise too long, it becomes sour, because the yeast plant is forming, at the same time, three other substances—alcohol, lactic acid (which gives an acid taste to the bread), and vinegar. Usually they form in such trifling amounts as to be quite unnoticeable. When the bread has become light enough, it is put into the oven to be baked.

A THOROUGH BAKING, AND A VALUABLE CRUST

Note the cleanly way of handling the food.

The baking serves the double purpose of cooking and thus making the starch appetizing, and of killing the yeast germs so that they will carry their fermentation no further. Bread that has not been thoroughly baked, if it is kept too long, will turn sour, because some of the yeast germs that have escaped will set to work again.

That part of the dough that lies on the surface of the loaf, and is exposed to the direct heat of the oven has its starch changed into a substance somewhat like sugar, known as dextrin, which, with the slight burning of the carbon, gives the outside, or crust, of bread its brownish color, its crispness, and its delicious taste. The crust is really the most nourishing part of the loaf, as well as the part that gives best exercise to the teeth.

Making Bread with Soda or Baking-Powders. Another method of giving lightness to bread is by mixing an acid like sour milk and an alkali like soda with the flour, and letting them effervesce[8] and give off carbon dioxid. This is the mixture used in making the famous "soda biscuit." Still another method is by the use of baking-powders, which are made of a mixture of some cheap and harmless acid powder with an alkaline powder—usually some form of soda. As long as these powders are kept dry, they will not act upon each other; but as soon as they are moistened in the dough, they begin to give off carbon dioxid gas.

AN IDEAL BAKERY WITH LIGHT, AIR, AND CLEANLINESS

Neither sour milk and soda nor baking-powder will make as thoroughly light and spongy and digestible bread as will yeast. If, however, baking-powders are made of pure and harmless materials, used in proper proportions so as just to neutralize each other, and thus leave no excess of acid or alkali, and if the bread is baked very thoroughly, they make a wholesome and nutritious bread, which has the advantage of being very quickly and easily made. The chief objection to soda or baking-powder bread is that, being often made in a hurry, the acid and the alkali do not get thoroughly mixed all through the flour, and consequently do not raise or lighten the dough properly, and the loaf or biscuit is likely to be heavy and soggy in the centre. This heavy, soggy stuff can be neither properly chewed in the mouth, nor mixed with the digestive juices, and hence is difficult to digest. If, however, soda biscuits are made thin and baked thoroughly so as to make them at least half or two-thirds crust, they are perfectly digestible and wholesome, and furnish a valuable and appetizing variety for our breakfast and supper tables.

A BASEMENT BAKERY—A MENACE TO THE PUBLIC HEALTH

Disease germs multiply in the dark and damp of the basement. The clothing hanging up in this bakery is a very probable source of infection.

Bran or Brown Bread. Flour made by grinding the wheat-berry without sifting the husks, or bran, out of it is called "whole-wheat" meal; and bread made from it is the brown "bran bread" or "Graham bread." It was at one time supposed that because brown bread contained more nitrogen than white bread, it was more wholesome and nutritious, but this has been found to be a mistake, because the extra nitrogen in the brown bread is in the form of husks and fibres, which the stomach is quite unable to digest. Weight for weight, white bread is more nutritious than brown. The husks and fibres, however, which will not digest, pass on through the bowels unchanged and stir up the walls of the intestines to contract; hence they are useful in small quantities in helping to keep the bowels regular. But, like any other stimulus, too much of it will irritate and disturb the digestion, and cause diarrhea; so that it is not best to eat more than one-fifth of our total bread in the form of brown bread. Dyspeptics who live on brown bread, or on so-called "health foods," are simply feeding their dyspepsia.

"Breakfast Foods." The same defect exists in most of the breakfast cereals which flood our tables and decorate our bill-boards. Some of these are made of the waste of flouring mills, known as "middlings," "shorts," or bran, which were formerly used for cow-feed. The claims of many of them are greatly exaggerated, for they contain no more nourishment, or in no more digestible form, than the same weight of bread; and they cost from two to five times as much. As they come on our tables, they are nearly seven-eighths water; and the cream and sugar taken with them are of higher food value than they are. They should never be relied upon as the main part of a meal.

Corn Meal. Corn meal is one of the richest meals in nutritive value for its price, as it has an abundance of starch and a small amount of fat. It is, however, poor in nitrogen, and like the other grains, in countries where wheat will grow, it is chiefly valuable for furnishing cakes, fritters, and mushes to give variety to the diet, and help to regulate the bowels.

Oatmeal. Oatmeal comes the nearest to wheat in the amount of nitrogen or protein, but the digestible part of this is much smaller than in wheat, and the indigestible portion is decidedly irritating to the bowels, so that if used in excess of about one-fifth of our total starch-food required, it is likely to upset the digestion.

Rye. Rye also contains a considerable amount of gluten, but is much poorer in starch than wheat is; and the bread made out of its flour—the so-called "black bread" of France and Germany—is dark, sticky, and inclined to sour readily. Most of the "rye" bread sold in the shops, or served on our tables, is made of wheat flour with a moderate mixture of rye to give the sour taste.

Rice. Rice consists chiefly of starch, and makes nutritious puddings or cakes, and may be used as a vegetable, in the place of potatoes, with meat and fish. It is, however, lacking in flavor, and when properly cooked, contains so much water that it has to be eaten in very large amounts to furnish much nutrition.

Potatoes. The only important starchy food outside of the grains is potatoes. These contain considerable amounts of starch, but mixed with a good deal of cellulose, or vegetable fibre, and water, so that, like rice, large amounts of them must be eaten in order to furnish a good fuel supply. They, however, make a very necessary article of diet in connection with meats, fish, and other vegetables.

As a rough illustration of the fuel value of the different starch foods, it may be said that in order to get the amount of nourishment contained in an ordinary pound loaf of wheat or white bread, it would be necessary to eat about seven pounds of cooked rice, as it comes on the table; about twelve pounds of boiled potatoes; or a bowl of oatmeal porridge about the size of a wash-basin.