The idea of starchy foods is usually connected with such substances as laundry starch, cornstarch, arrow root, etc. These are, of course, more concentrated forms of starch than potatoes, rice, etc. Many starchy foods contain other ingredients, and some are especially rich in proteids.

The following table may help to make this clear (Atwater):—

It is estimated that starch composes one-half of peas, beans, wheat, oats and rye, three-fourths of corn and rice, one-fifth of potatoes. Vegetable proteids, as already stated, are less easily digested than those belonging to the animal kingdom, therefore it must be remembered that a purely vegetable diet, even though it may be so arranged as to provide the necessary protein, is apt to over-tax the digestive organs more than a mixed diet from both the animal and vegetable kingdoms. Much depends upon the cooking of the starchy foods in order to render them digestible. (Study chapter on Digestion in the Public School Physiology.)

The digestion of starch—which is insoluble in cold water—really begins with the cooking, which by softening the outer coating or fibre of the grains, causes them to swell and burst, thereby preparing them for the chemical change which is caused by the action of the saliva in converting the starch into a species of sugar before it enters the stomach. Substances which are insoluble in cold water cannot be absorbed into the blood, therefore are not of any value as food until they have become changed, and made soluble, which overtaxes the digestive organs and causes trouble. The temperature of the saliva is too low to dissolve the starch fibre unaided. Each of the digestive juices has its own work to do, and the saliva acts directly upon the starchy food; hence the importance of thoroughly masticating such food as bread, potatoes, rice, cereals, etc. The action of heat, in baking, which causes the vapor to rise, and forms the crust of starchy food, produces what is called dextrine, or partially digested starch. Dextrine is soluble in cold water, hence the ease with which crust and toast—when properly made—are digested. It is more important to thoroughly chew starchy food than meat, as it is mixed with another digestive juice, which acts upon it in the stomach.

Sugars.

There are many varieties of sugar in common use, viz.: cane sugar, grape sugar or glucose, and sugar of milk (lactose). As food, sugars have practically the same use as starch; sugar, owing to its solubility, taxes the digestive organs very little. Over-indulgence in sugar, however, tends to cause various disorders of assimilation and nutrition. Sugar is also very fattening, it is a force producer, and can be used with greater safety by those engaged in active muscular work. Cane sugar is the clarified and crystallized juice of the sugar cane. Nearly half the sugar used in the world comes from sugar cane, the other half from beet roots. The latter is not quite so sweet as the cane sugar. Sugar is also made from the sap of the maple tree, but this is considered more of a luxury; consequently, not generally used for cooking purposes.

Molasses and treacle are formed in the process of crystallizing and refining sugar. Treacle is the waste drained from moulds used in refining sugar, and usually contains more or less dirt.

Glucose, or grape sugar, is commonly manufactured from starch. It is found in almost all the sweeter varieties of fruit. It is not so desirable for general use as cane sugar.

Honey is a form of sugar gathered by bees from the nectar of flowering plants, and stored by them in cells. Honey contains water 16.13, fruit sugar 78.74, cane sugar 2.69, nitrogenous matter 1.29, mineral matter 0.12 per cent. (Konig.)

Grains.

While the grains contain less proteid than the legumes, they are more valuable on account of the variety of the nutrients contained in them, and are more easily adapted to the demands of the appetite. They, however, require long, slow cooking in order to soften the fibre and render the starch more soluble. Among the most important we may place:

A wheat kernel may be subdivided into three layers. The first or outer one contains the bran; second, the gluten, fats and salts; third, the starch. Some of the mineral matter for which wheat is so valuable is contained in the bran, hence the value of at least a portion of that part of the wheat being included in bread flour—not by the addition of coarse bran (which is indigestible) to the ordinary flour, but by the refining process employed in producing whole wheat flour. While wheat is used in other forms, its principal use as food is in the form of flour.

The following table, giving the composition of bread from wheat and maize, will be of interest (Stone):—

The most valuable food product manufactured from flour is bread.

Bread contains so many of the ingredients required to nourish the body, viz.: fat, proteid, salts, sugar and starch, that it may well be termed the "staff of life." As it does not contain enough fat for a perfect food the addition of butter to it renders it more valuable as an article of diet. Mrs. Ellen H. Richards gives the following explanation of what constitutes ideal bread: "(1) It should retain as much as possible of the nutritive principles of the grain from which it is made; (2) it should be prepared in such a manner as to secure the complete assimilation of these nutritive principles; (3) it should be light and porous, so as to allow the digestive juices to penetrate it quickly and thoroughly; (4) it should be nearly or quite free from coarse bran, which causes too rapid muscular action to allow of complete digestion. This effect is also produced when the bread is sour." Bread is made from a combination of flour, liquid (either milk or water), and a vegetable ferment called yeast (see yeast recipes). The yeast acts slowly or rapidly according to the temperature to which it is exposed. The starch has to be changed by the ferment called diastase (diastase is a vegetable ferment which converts starchy foods into a soluble material called maltose) into sugar, and the sugar into alcohol and carbonic acid gas (carbon dioxide), when it makes itself known by the bubbles which appear and the gradual swelling of the whole mass. It is the effect of the carbonic acid gas upon the gluten, which, when checked at the proper time before the ferment becomes acetic (sour) by baking, produces the sweet, wholesome bread which is the pride of all good housekeepers. The kneading of bread is to break up the gas bubbles into small portions in order that there may be no large holes and the fermentation be equal throughout. The loaf is baked in order to kill the ferment, to render the starch soluble, to expand the carbonic acid gas and drive off the alcohol, to stiffen the gluten and to form a crust which shall have a pleasant flavor. Much of the indigestibility of bread is owing to the imperfect baking; unless the interior of the loaf has reached the sterilizing point, 212° F., the bacteria contained in the yeast will not be killed, and some of the gas will remain in the centre of the loaf. The scientific method of baking bread is to fix the air cells as quickly as possible at first. This can be done better by baking the bread in small loaves in separate pans, thereby securing a uniform heat and more crust, which is considered to be the most easily digested part of the bread. Some cooks consider that long, slow baking produces a more desirable flavor and renders bread more digestible. One hundred pounds of flour will make an average of one hundred and thirty-five pounds of bread. This increase of weight is due to the addition of water.

Macaroni is a flour preparation of great food value. It contains about six per cent. more gluten than bread, and is regarded by Sir Henry Thompson as equal to meat for flesh-forming purposes. Dieticians say that macaroni, spaghetti and vermicelli are not used so extensively as their value deserves.

Buckwheat is the least important of the cereals.

Rye is almost equal to wheat in nutritive value. Its treatment in regard to bread making is similar to that of wheat.

Corn contains fat, proteid and starch, and produces heat and energy. It is very fattening, and when eaten as a vegetable is considered difficult of digestion. Cornmeal is a wholesome food; it contains more fat than wheat flour, and less mineral matter.

Rice constitutes a staple food of a great many of the world's inhabitants. It contains more starch than any other cereal, but when properly cooked is very easily digested. It should be combined with some animal food, as it contains too little nitrogen to satisfy the demands of the system. It forms a wholesome combination with fruit, such as apples, peaches, prunes, berries, etc.

Barley is almost equal to wheat in nutritive value. It contains more fat, mineral matter and cellulose (cellulose is often called indigestible fibre, as it resists the solvent action of the digestive juices, and is of no value as a nutrient), and less proteid and digestible carbohydrates.

Oatmeal is one of the most valuable foods. Oats contain fat, proteid, salts and cellulose, in addition to a large percentage of starch. The nutritive value of oatmeal is great, but much depends upon the manner of cooking. (See recipes.) People who eat much oatmeal should lead a vigorous outdoor life. The following analysis of oatmeal is given (Letheby):—

Vegetables.

Legumes—peas, beans and lentils—have an exceedingly leathery envelope when old; and unless soaked for a long time in cold water—in order to soften the woody fibre—and are then cooked slowly for some hours, are very indigestible. Pea and bean soups are considered very nutritious. Lentils grow in France; they are dried and split, in which form they are used in soups.

Potatoes are the most popular of all the tubers. As an article of diet they possess little nutritive value, being about three-fourths water. They contain some mineral matter, hence the reason why they are better boiled and baked in their skins, so as to prevent the escape of the salts into the water. Potatoes are more easily digested when baked than cooked in any other form.

Beets contain between 85 and 90 per cent. of starch and sugar, some salts, and a little over one per cent. of proteid matter. Young beets, either in the form of a vegetable or a salad, are considered to be very wholesome.

Carrots, turnips, parsnips and oyster plant, although containing a large percentage of water, are considered valuable as nutrients, the turnip being the least nutritious.

Green vegetables do not contain much nutriment, and are chiefly valuable as affording a pleasing variety in diet; also for supplying mineral matter and some acids. In this class we may include cabbage, cauliflower, spinach, lettuce and celery.

Tomatoes are wholesome vegetables; on account of the oxalic acid they contain they do not always agree with people of delicate digestion.

Cucumbers are neither wholesome nor digestible.

Asparagus is a much prized vegetable. The substance called asparagin which it contains is supposed to possess some value.

Rhubarb is a wholesome vegetable.

Onions, garlic, and shallots are valuable both as condiments and eaten separately. They contain more nutrients than the last vegetables considered.