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.
COCOA AND CHOCOLATE.
Cocoa is prepared from the roasted seeds of the tree Theobroma cacao, of the order Byttneriaceæ. It sometimes appears in commerce as “cocoa-nibs” (i. e. partially ground), but it is more frequently sold in the powdered state, either pure or mixed with sugar and starch, and also often deprived of about one-half of its fat. Chocolate usually consists of cocoa-paste and sugar flavoured with vanilla, cinnamon, or cloves, and commonly mixed with flour or starch. According to Wanklyn, the average composition of cocoa is as follows:—
| Per cent. | |
| Cocoa butter | 50·00 |
| Theobromine | 1·50 |
| Starch | 10·00 |
| Albumin, fibrine and gluten | 18·00 |
| Gum | 8·00 |
| Colouring matter | 2·60 |
| Water | 6·00 |
| Ash | 3·60 |
| Loss, etc. | 0·30 |
R. Benzeman[14] has furnished the following averages of the results obtained by the analysis of cocoa and chocolate. The air-dried cocoa berries gave—husks, 13·00 per cent.; nibs, 87·00 per cent.:—