Coffee is the seed of the Caffea Arabica, indigenous to Abyssinia and southern Arabia, and since naturalised in the West Indies, Ceylon, Brazil, and other tropical countries. Its importance as an almost universal beverage is only equalled by that of tea. The ancient history of coffee is shrouded in great obscurity. It was unknown to the Romans and Greeks, but its use is said to have been prevalent in Abyssinia from the remotest time, and in Arabia it formed an article of general consumption during the fifteenth century. From its introduction, in 1575, into Constantinople by the Turks, it gradually made its way into all civilised countries. In 1690 it was carried by the Dutch from Mocha to Java, whence specimens of the tree were taken to Holland and France. Coffee houses were opened in London about the middle of the seventeenth century, and in 1809 the first cargo of coffee was shipped to the United States. As with many other articles of diet, the adulteration of coffee has kept well apace with its increased consumption. The bean is deprived of its external fleshy coatings before exportation, and is met with in commerce in a raw, roasted, or ground condition. Bell[9] gives the following analyses of two samples of coffee, both in the raw and roasted state:—

Other authorities have obtained the following results:—

It will be noticed from these analyses that the amount of sugar is greatly diminished by the process of roasting. According to some analysts, the proportion of fat experiences an increase, but it is more probable that this constituent is simply rendered more susceptible to the action of solvents by a mechanical alteration of the structure of the berry. Recent determinations of the ash in coffee place its average proportion at 4 per cent.; 3·24 being soluble in water, and 0·74 per cent. insoluble. The soluble extract in roasted coffee usually amounts to about 30 per cent.

An analysis made by Beckurts and Kauder[10] gives the general composition of roasted chicory, dried at 107°, as follows:—

The most common adulterations to which coffee is liable consist in the addition of chicory, caramel, and numerous roasted grains, such as corn, wheat, and rye, as well as such roots and seeds as dandelion, mangold wurzel, turnips, beans, peas, etc. The roasted and ground article is naturally most exposed to falsification, although letters patent have been issued for the fictitious manufacture of a pressed “coffee bean,” containing absolutely no coffee. The addition of chicory is by far the most prevalent adulteration of coffee. Of thirty-four samples examined by Hassall, thirty-one (91 per cent.) contained this root. In regard to the moral aspects of its use, it can safely be asserted that, while the addition of chicory to coffee is largely sanctioned, and indeed demanded by the existing tastes of many coffee-drinkers, its use constitutes a true adulteration, and should be condemned, unless its presence is prominently stated on the label of the package. In chicory the active principles of coffee, which exert valuable physiological effects on the system (viz. caffeine, the essential oil, etc.), are totally absent; moreover, its comparative cheapness is a constant temptation to employ a proportion largely in excess of the amount requisite to produce any alleged improvement in the flavour of the resulting admixture.

The sophistications of coffee may be detected, in a general way, by physical tests, by chemical analysis, and by microscopic examination, in which processes great aid is derived from the characteristic properties exhibited by the pure roasted and ground berry which distinguish it from its more usual adulterants.

(a) Physical Examination.—The following tests, while not always decisive in their results, are often of service.

A small portion of the suspected sample is gently placed upon the surface of a beaker filled with cold water, and allowed to remain at rest for about fifteen minutes. If pure, the sample does not imbibe the water, but floats upon the surface without communicating much colour to it; if chicory or caramel be present, these substances rapidly absorb moisture and sink, producing brownish-red streaks in their descent, which, by diffusion, impart a very decided tint to the entire liquid. A similar coloration is caused by many other roasted roots and berries, but not so quickly or to so great an extent. The test may be somewhat modified by shaking the sample with cold water, and then allowing the vessel to stand aside for a short time. Pure coffee rises to the surface, little or no colour being imparted to the water; chicory, etc., fall to the bottom as a sediment, and give a brownish colour to the liquid.

If a small quantity of the sample is placed upon a clean plate of glass, and moistened with a few drops of water, the pure coffee berries remain hard, and offer resistance when tested with a needle; most grains employed for their adulteration become softened in their texture.

A considerable portion of the mixture is treated with boiling water and allowed to settle. Genuine coffee affords a clear and limpid infusion; many foreign grains yield a thick gummy liquor, resulting from the starchy and saccharine matters contained. An infusion of pure coffee, if treated with solution of cupric acetate and filtered, will show a greenish-yellow colour; if chicory be present, the filtrate will be reddish-brown. As a rule, samples of ground coffee which are much adulterated, pack together when subjected to a moderate pressure.

Owing to the low density of a coffee infusion (due to its almost entire freedom from sugar), as compared with that of the infusions of most roots and grains, it has been suggested by Messrs. Graham, Stenhouse and Campbell, to apply the specific gravity determination of the infusion obtained from the suspected sample as a means for detecting adulteration. The results afforded are fairly approximate. The solution is prepared by boiling one part of the sample with ten parts of water and filtering. The following table gives the densities, at 15°·5, of various infusions made in this manner:—

Assuming the gravity of the pure coffee infusion to be 1·0086, and that of chicory to be 1·0206, the approximate percentage of coffee, C, in a mixture, can be obtained by means of the following equation, in which D represents the density of the infusion:—

C = 1·00(1·020 - D) 12.

This was tested by mixing equal parts of coffee and chicory, and taking the specific gravity of the infusion; it was 1·01408, indicating the presence of 49 per cent. of coffee. Some idea of the amount of foreign admixture (especially chicory) in ground roasted coffee may be formed from the tinctorial power of the sample. It has already been mentioned that coffee imparts much less colour to water than do most roasted grains and roots. The table below shows the weights of various roasted substances which must be dissolved in 2·000 parts of water in order to produce an equal degree of colour:[11]—

The comparative colour test may also be applied as follows:[12]—One gramme each of the sample under examination, and of a sample prepared by mixing equal parts of pure coffee and chicory, are completely exhausted with water, and the infusions made up to 100 c.c. or more; 50 c.c. of the filtered extract from the suspected sample are then placed in a Nessler cylinder, and it is determined by trial how many c.c. of the extract from the standard mixture, together with enough distilled water to make up the 50 c.c., will produce the same colour. In calculating the chicory present, it is assumed that this substance possesses three times the tinctorial power of coffee.

(b) Chemical Examination.—Some of the chemical properties of roasted coffee afford fairly reliable means for the detection of an admixture of chicory. Coffee ash dissolves in water to the extent of about 80 per cent.; of the ash of roasted chicory only about 35 per cent. is soluble. Coffee ash is almost free from silica and sand, which substances form a notable proportion of the constituents of the ash of chicory.

The following (see p. 36) are the results obtained by the writer from the analysis of the ash of coffee and chicory.

It will be observed from these analyses, that the most distinctive features presented by coffee ash are the absence of soda, and the small amounts of chlorine, ferric oxide and silica present. In these respects, it is very different from the ash of chicory. The proportion of phosphoric acid found in the latter is in excess of that given by some authorities. Several analyses of chicory ash have been made by the author, and, in every instance, the amount of phosphoric acid was over 8 per cent.; in one sample of the ash of commercial chicory it approximated 13 per cent.

Blyth gives the annexed table, showing the characteristic differences between coffee and chicory ash:[13]—

The following formula has been suggested for determining the percentage of pure coffee, in mixtures:—

C = 2 (100S - 174)3

where S represents the percentage of soluble ash.

Another noteworthy difference between roasted coffee and chicory, is the amount of sugar contained. As a rule, in roasted coffee, it ranges from 0·0 to 1·2 per cent.; in roasted chicory, it varies from 12· to 18· per cent. The quantity of sugar in a sample can be determined by Fehling’s method as follows:—

A standard solution of pure cupric sulphate is first prepared by dissolving 34·64 grammes of the crystals (previously ground and dried by pressing between bibulous paper) in about 200 c.c. of distilled water; 173 grammes of pure Rochelle salt are separately dissolved in 480 c.c. of a solution of sodium hydroxide of sp. gr. 1·14. The solutions are then mixed and diluted with distilled water to one litre. Each c.c. of the above solution represents 0·05 gramme of grape sugar. The test is applied by taking 10 c.c. of the copper solution, adding about four times its volume of water, and bringing it to the boiling point. The coffee infusion is then gradually added from a burette, until the copper salt is completely reduced to the red sub-oxide, which point is recognised by the disappearance of its blue colour, and can be more accurately determined by acidulating the filtered fluid with acetic acid and testing it (while still hot) for any remaining trace of copper with potassium ferrocyanide. In preparing the coffee solution for the foregoing test, it is advisable to exhaust a weighed quantity of the sample with hot water. The infusion is treated with basic plumbic acetate so long as a precipitate forms; it is then filtered, the precipitate being well washed, and the lead contained is removed by conducting sulphuretted hydrogen gas through the fluid which is subsequently again filtered and boiled until the dissolved gas is expelled. The sugar determination is now made. Wanklyn employs the following equation to estimate the amount of chicory in an adulterated sample:—

E = (S - 1)100 14,

where E is the percentage of chicory, and S the percentage of sugar.

According to the analysis of KÖnig, the proportions of sugar and other constituents in some of the adulterants of coffee, are as follows:—

Estimations of the amount of sugar obtained upon boiling the suspected coffee with water containing a little sulphuric acid (see p. 37), and the proportion of the sample which is soluble in hot water should be made. The presence of chicory is shown by a decided increase in the amount of soluble substances; that of rye, by the notable quantity of sugar produced by the inversion with acid, due to the starch contained in the grain.

In this connection, the following determinations of Krausch are of interest:—

The presence of roasted rye, corn, and other grains in coffee, may be qualitatively recognised by testing the cold infusion of the sample with iodine solution for starch, which is not contained in a ready formed state in coffee. Caffeine is absent in chicory and the other usual adulterants of coffee, and the estimation of this alkaloid is of decided service (see p. 21). Roasted coffee contains about 1 per cent. of caffeine.

A popular brand of ground coffee received by the author for examination, and labelled “Prepared Java Coffee,” had the following approximate composition:—Coffee, 38; peas, 52; rye, 2; and chicory, 7 per cent.

A sample of “acorn” coffee, analysed by KÖnig, gave the following results:—

The non-nitrogenous constituents contained from 20 to 30 per cent. of starch, and from 6 to 8 per cent. of tannic acid.

The composition of the well-known German coffee-substitutes, prepared by Behr Bros., is stated to be as follows:—

“Rye Coffee-substitutes.”

“Malt Coffee-substitute.”

The raw coffee bean is sometimes subjected to a process termed “sweating,” which consists in treating it with moist steam, the object being to artificially reproduce the conditions present in the holds of vessels, by means of which the bean is increased in size, and also somewhat improved in colour and flavour. Another form of manipulation, analogous to the facing of tea, is to moisten the raw bean with water containing a little gum, and agitate it with various pigments, such as indigo, Prussian blue, Persian berries, turmeric, alkanet, Venetian red, soap-stone, chrome-yellow, and iron ochre. Mexican coffees are sometimes made to resemble the more expensive Java in appearance. The chemist of the New York City Board of Health has found in the quantity of such treated coffee commonly taken to make a cup of the beverage 0·0014 gramme of cupric arsenite. Indigo may be detected in the artificially coloured product by treating a considerable portion of the sample with dilute nitric acid, filtering and saturating the filtrate with sulphuretted hydrogen. If indigo be present, it can now be extracted upon agitating the solution with chloroform. Alkanet root and Prussian blue are separated by warming the coffee with solution of potassium carbonate, from which these pigments are precipitated upon addition of hydrochloric acid.

(c) Microscopic Examination.—Great aid to the chemical investigation is afforded by the microscopic examination of ground coffee. It is necessary to first become familiar with the appearance of the genuine article—low magnifying powers being employed—and then make comparative examinations of the adulterant suspected to be present.

The coffee bean mainly consists of irregular cells inclosed in very thick walls which are distinguished by uneven projections. The cells contain globules of oil. Most of the roots added to coffee exhibit a conglomeration of cells (provided with thin walls) and groups of jointed tubes, often quite similar to one another in structure. The microscopic appearance of some of the starch granules, occasionally met with in coffee mixtures, is represented on p. 100.

Of 151 samples of ground coffee recently purchased at random and tested by various American chemists, 69 (45·7 per cent.) were found to be adulterated.