Human Foods and Their Nutritive Value, Harry Snyder [free e books to read TXT] 📗
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214. Composition of Tea.—Black and green teas are produced from the same species of plant, but owe their difference in color as well as flavor and odor to methods of preparation. The same plant may yield several grades of both green and black tea. To produce black tea, the leaves are bruised to liberate the juices, allowed to ferment a short time, which develops the color, and then dried.[73] For green tea the fresh leaves are roasted or steamed, then rolled and dried as quickly as possible to prevent fermentation. The smaller leaves and the first picking produce the finest quality of tea. The characteristic flavor and odor of tea are imparted by a volatile oil, although the odor is sometimes altered by the tea being brought in contact with orange flowers, jessamine, or the fragrant olive. There are also present in tea an alkaloid, theine, which gives the peculiar physiological properties, and tannin, upon which depends largely the strength of the tea infusion. The composition of tea is as follows:
Tea Green
Tea Black
Tea Tannin, per cent 12.91 10.64 4.89 Theine, per cent 3.30 3.20 3.30 Ash, per cent 4.97 4.92 4.93 Fiber, per cent 10.44 10.06 10.07 Protein, per cent (all insoluble) 37.33 37.43 38.90
It will be noticed that green tea contains twice as much tannin as black tea; during the fermentation which the black tea undergoes, some of the tannin is decomposed. There is a large amount of protein in tea, but it is of no food value, because of its insolubility. About half of the ash is soluble. The tannin is readily soluble, and for this reason green tea especially should be infused for a very short time and never boiled. Tannin in foods in large amounts may interfere with the normal digestion of the protein compounds, because it coagulates the albumin and peptones after they have become soluble, and thus makes additional work for the digestive organs.
215. Judging Teas.—Teas are judged according to: (1) the tea as it appears prepared for market, (2) the infusion, and (3) the out-turn after infusion. The color should be uniform; if a black tea, it should be grayish black, not a dead black. The leaves should be uniform in size or grade. The quality and grade are dependent upon flavor, and, with the strength of the infusion, are determined by tasting. This work is rapidly done by the trained tea taster. The out-turn should be of one color; no bright green leaves should be present; evenness of make is judged by the out-turn. The flavor of a tea is largely a matter of personal judgment, but from a physiological point of view black teas are given the preference.
216. Adulteration of Tea.—A few years ago tea was quite extensively adulterated, but the strict regulation of the government regarding imported tea has greatly lessened adulteration. The most common form was the use of spent leaves, i.e. leaves which had been infused. Leaves of the willow and other plants which resemble tea were also used, as well as large quantities of tea stems. Facing or coloring is also an adulteration, since it is done to give poor or damaged tea a brighter appearance. "Facing consists in treating leaves damaged in manufacture or which from age are inferior, with a mixture containing Prussian blue, turmeric, indigo, or plumbago to impart color or gloss, and with a fraudulent intent. There is no evidence that the facing agents are deleterious to health in the small quantities used, but as they are used for purposes of deception, they should be discouraged."[73] Facing and the addition of stems are the chief adulterations practiced at present.
217. Food Value and Physiological Properties of Tea.—Tea infusion does not contain sufficient nutrients to entitle it to be classed as a food. It is with some persons a stimulant. The caffein or theine in tea is an alkaloid that has characteristic physiological properties. In doses of from three to five grains, according to the United States Dispensatory, "it produces peculiar wakefulness." Larger doses produce intense physical restlessness, mental anxiety, and obstinate sleeplessness. "It has no effect upon the motor nerves, but is believed to have a visible effect upon the sensatory nerves." (United States Dispensatory.) Experiments with animals show that it causes elevation of the arterial pressure. It is used as a cardiac stimulant. The quantity of theine consumed in a cup of tea is about 4/5 of a grain, or ¼ of a medicinal dose.
Fig. 54.—Coffee Berries. 1, Mocha; 2, Java; 3, Rio.
218. Composition of Coffee.—The coffee tree is an evergreen cultivated in the tropics. It grows to a height of 30 feet, but when cultivated is kept pruned to from 6 to 10 feet. The fruit, which resembles a small cherry, with two seeds or coffee grains embedded in the pulp, is dried and the seeds removed, cleaned, and graded. Coffee has an entirely different composition from tea; it is characterized by a high per cent of fat and soluble carbohydrates, and also contains an essential oil and caffein, an alkaloid identical with theine. Tannic acid, not as free acid, is combined with caffein as a tannate.
Coffee Roasted
Coffee Per Cent Per Cent Water 11.23 1.15 Ash 3.92 4.75 Fat 12.27 14.48 Sugar, etc. 0.66 8.55 Protein 12.07 13.98 Caffein 1.21 1.24
The high per cent of sugar and other soluble carbohydrates in roasted coffee is caused by the action of heat upon the non-nitrogenous compounds. Coffee cannot be considered a food, because only a comparatively small amount of the nutrients are soluble and available. It is a mildly stimulating beverage. With some individuals it appears to promote the digestive process, while with others its effect is not beneficial. Coffee is more extensively used in this country than tea, and is subject to greater adulteration. It is adulterated by facing and glazing; i.e. coloring the berries to resemble different grades and coating them with caramel and dextrine. Spent coffee grains and coffee that has been extracted without grinding are also used as adulterants. Imitation berries made of rye, corn, or wheat paste, molded, colored with caramel, and baked have been found mixed with genuine coffee berries. Roasted cereals and chicory are used extensively to adulterate ground coffee. Chicory is prepared from the root of the chicory plant, which belongs to the same family as the dandelion. It is claimed by some that a small amount of chicory improves the flavor of coffee. However, when chicory is added to coffee, it should be so stated on the label and the amount used given. The dextrine and sugar used in glazing are browned or caramelized during roasting and impart a darker color to the infusion, making it appear better than it really is. The glazing also makes the coffee retain moisture which would otherwise be driven off during roasting. Coffee contains such a large per cent of oil that the berries generally float when thrown on water, while the imitation berries sink. Chicory also sinks rapidly and colors the water brown, while the coffee remains floating for some time.
There are three kinds of coffee in general use: Java, Mocha, and Rio or Brazil. The Brazil coffee has the largest berry and is usually styled by dealers as "low" or "low middlings." The Java coffee berries are smaller and paler in color, the better grades being brown. Mocha usually commands the highest price in commerce. The seeds are small and dark yellow before roasting.
219. Cereal Coffee Substitutes.
"A few of these preparations contain a little true coffee, but for the most part they appear to be made of parched grains of barley, wheat, etc., or of grain mixed with pea hulls, ground corncobs, or wheat middlings. It is said that barley or wheat parched, with a little molasses, in an ordinary oven, makes something indistinguishable in flavor from some of the cereal coffees on the market. If no coffee is used in the cereal preparations, the claim that they are not stimulating is probably true. As for the nutritive value, parching the cereals undoubtedly renders some of the carbohydrates soluble, and a part of this soluble matter passes into the decoction, but the nutritive value of the infusion is hardly worth considering in the dietary."[56]
220. Cocoa and Chocolate Preparations.—Cocoa and chocolate are manufactured from the "cocoa bean," the seed of a tree native to tropical America. The beans are inclosed in a lemon-yellow, fleshy pod. They are removed from the pulp, allowed to undergo fermentation, and dried by exposure to the air and light, which hardens them and gives them a red color. This method produces what is known as the "fermented cocoa." For the "unfermented cocoa," the beans are dried without undergoing fermentation. Fermentation removes much of the acidity and bitterness characteristic to the unfermented bean, and when properly regulated develops flavor. The original bean contains about 50 per cent fat, part of which is removed in preparing the cocoa. This fat is sold as cocoa butter. In the preparation of some brands of cocoa, alkalies, such as soda and potash, are used to form a combination with the fat to prevent its separating in oily globules. This treatment improves the appearance of the cocoa, but experiments show the albumin to be somewhat less digestible and the soap-like product resulting not as valuable a food as the fat. Such preparations have a high per cent of ash. There is no objection from a nutritive point of view to a cocoa in which the fat separates in oily globules.
221. Composition of Cocoa.—The cocoa bean, when dried or roasted and freed from its husk and ground, is sold as cracked cocoa, or cocoa nibs. From cocoa nibs the various cocoa and chocolate preparations are made. Cocoas vary in composition according to the extent to which the fat is removed during the process of manufacture and the nature and extent to which other ingredients are added. An average cocoa contains about 20 per cent of proteids, and 30 per cent fat, also starch, sugar, gums, fiber, and ash, as well as theobromine, a material very similar to theine and caffein in tea and coffee, but not such an active stimulant. Cocoa is not easily soluble, but it may be ground so fine that a long time is required for its sedimentation; or sugar or other soluble material may be added during the process of manufacture to increase the specific gravity of the liquid to such an extent that the same object is attained without such fine grinding. The first method is to be preferred. Cocoa and its preparations are richer in nutritive substances than tea and coffee and have this added advantage that both the soluble and insoluble portions become a part of the beverage. Owing to the small amount used for a cup of cocoa, independent of the milk it does not add much in the way of nutrients to the ration.
222. Chocolate.—Plain chocolate is prepared from cocoa nibs without "removal of the fat or other constituents except the germ." It differs in chemical composition from cocoa by containing more fat and less protein; it has nearly the same chemical composition as the cocoa nibs. It is officially defined as containing "not more than 3 per cent of ash insoluble in water, 3½ per cent of
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