Composition

Coffee consists of the berries or seeds of Coffea arabica, which are dried, roasted, ground, and subjected to infusion. The coffee drunk in the United States is mainly imported from South and Central America, Mexico, and Java, 63 per cent being imported from Brazil. The Rio berry is smaller than that from Java. The composition of coffee beans varies somewhat, but an approximate idea of it is obtained from the following table from Konig, which gives the percentage of the important ingredients:

Water..................................................... 1.15

Fat....................................................... 14 48

Crude fibre................................................ 19.89

Ash....................................................... 4.75

Caffeine................................................... 1.24

Albuminoids............................................... 13.98

Other nitrogenous matter.................................... 45.09

Sugar, gum, and dextrin..................................... 1.66

The exhilarating effect of coffee is said to be caused by the ingredients caffeine, caffeotannic and caffeic acids, and a volatile oil developed during roasting.

The coffee berry contains no starch, and Wiley has shown that its principal carbohydrate is cane sugar or sucrose. There are present also a substance allied to dextrin and a reducing sugar. The well-known stimulant effect of coffee upon the nervous system is mainly due to the alkaloid caffeine, which is chemically identical with theine and possesses the same physiological properties, its action being chiefly upon the nerves and kidneys. Coffee also contains a little aromatic oil which is moderately stimulating to the nervous system. It has less oil than tea.

Method Of Preparation

The preparation which the coffee beans require consists of drying them by roasting at a temperature of fully 2000 C, after which they are ground into small fragments to facilitate the solution of their ingredients by hot water. The heat converts the sugar of the beans into caramel and develops volatile and aromatic substances to which the agreeable aroma of the coffee is due. These substances being volatile, the aroma soon forsakes the beans, and they should not be roasted or ground long before they are to be used. The roasting also liberates gases in the beans, which cause them to increase in bulk while losing in weight.

The methods of preparing coffee as a beverage are three - namely, (1) filtration, (2) infusion, and (3) decoction or boiling.

(1) In filtration boiling water is allowed to percolate slowly through finely ground coffee. Air should be excluded as much as possible during the process; otherwise the oxygen alters the aroma. According to von Liebig, filtration only dissolves from 11 to 15 per cent of the coffee instead of 20 or 21 per cent, which is obtainable by other means.

(2) Infusion is the common mode of preparation of coffee employed in this country and in Europe. It is said to reduce the exciting influence of strong coffee without destroying its aroma or otherwise altering it. In conducting this process the finely ground coffee is put into water previously boiled, but removed from the fire, and allowed to stand for about ten minutes at a temperature of 1800 or 1900 F.

(3) Decoction is the method principally used in Turkey and elsewhere in the East. The coffee beans are ground to powder and placed in cold water, which is then heated to boiling. The beverage is drunk without straining. If boiled but a few minutes some aroma still remains, but it is soon driven off, and continued boiling extracts more caffeine than is obtainable by infusion.

Coffee long boiled or left standing in the coffee pot over the fire, as in the case of tea, becomes more and more indigestible from extraction of tannin.

Soft water extracts more coffee from the berries than hard, as it does from tea leaves.

Coffee should always be made from newly roasted and ground beans; and when economy is to be considered, or when strength and aroma are both desired, a larger proportion of the soluble ingredients may be obtained by combining the second and third processes, as described by Yeo: "After first preparing an infusion by passing boiling water over the coffee, the grounds left should be boiled in more water, and the boiling decoction thus obtained should be poured over another portion of freshly ground coffee; this, in turn, is also boiled with more water, to be used again with fresh coffee in the same manner, and so on. By this method all the soluble matters in the coffee are extracted and none of the aroma is needlessly dissipated." Ready-made coffee is sometimes preserved with condensed milk and sugar in tin cans. This preparation merely requires to be put into a cup of hot water to be fit for drinking.

Physiological Action

Good Effects

Coffee, when taken as a beverage, has well-marked physiological effects, chiefly upon the muscular, vascular, and nervous systems. It removes the sensation of fatigue in the muscles and increases their functional activity; it allays hunger to a limited extent; it strengthens the heart action, and constitutes a valuable cardiac stimulant in some forms of collapse by its moderate quickening effect upon the pulse and influence upon the vascular tone; it acts as a diuretic, and increases the excretion of urea; it has a mildly sudorific influence; it counteracts nervous exhaustion and stimulates nerve centres. It is used sometimes as a nervine in cases of migraine, and there are many persons who can sustain prolonged mental fatigue and strain from anxiety and worry much better by the use of strong black coffee. In low delirium, or when the nervous system is overcome by the use of narcotics as in the case of opium poisoning, or by alcohol, or by excessive haemorrhage, strong black coffee is serviceable to keep the patient from falling into the drowsiness which soon merges into coma.

In such cases as much as half a pint of strong black coffee may be injected into the rectum.

Drunk in moderation, coffee is a mild stimulant to gastric digestion. In the bowels coffee has an opposite effect to that of tea, for it stimulates peristalsis, and for many people, when drunk early in the morning, it possesses a distinctly laxative effect. It thus indirectly benefits the liver. Strong coffee with a little lemon juice or brandy is often useful in overcoming a malarial chill or a paroxysm of asthma. It is the universal testimony of army officers that coffee is indispensable for troops in service to relieve fatigue and improve their spirits.

The stimulating and diuretic effect of coffee is more decided when it is taken into an empty stomach.

The nutrient value of coffee alone is too slight to be considered, but the addition of sugar and milk, as in the case of tea, makes it a valuable food. It does, however, possess some effect in diminishing tissue waste. The very general fondness which exists for the taste of coffee makes it a useful means of flavouring many kinds of foods for invalids, such as jellies, custards, etc. When the taste of milk is objected to, the addition of a very little coffee will often overcome the dislike for it.

Coffee is a useful temporary cardiac stimulant for children suffering collapse, but should not be given them as a daily beverage.