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:—

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.:—

Recent analysis of shelled cocoa-beans, made by Boussingault, gave the following results:—

Dr. Weigman[15] obtained the following results from an examination of several varieties of the shelled beans:—

The most important constituents of cocoa are the fat (cocoa-butter), and the alkaloid (theobromine).

Cocoa butter forms a whitish solid of 0·970 specific gravity, fusing at 30°, and soluble in ether and in alcohol.

Theobromine (C7H8N4O2) crystallises in minute rhombic prisms, which are insoluble in benzol, but dissolve readily in boiling water and alcohol. It sublimes at 170°. Theobromine is exceedingly rich in nitrogen, containing over 20 per cent. of the element. In this and many other respects it bears a great resemblance to theine.

The proportion of mineral ash in cocoa varies from 3·06 to 4·5 per cent.

James Bell[16] gives the following composition of the ash of Grenada cocoa nibs:—

The most characteristic features of the ash of genuine cocoa are its great solubility, the small amounts of chlorine, carbonates, and soda, and the constancy of the proportion of phosphoric acid contained. Bell has also analysed several samples of commercial cocoa. The following will serve to illustrate their general composition:—

The comparatively low percentage of ash contained in prepared cocoas and chocolate, is of use in indicating the amount of real cocoa present in such mixtures. A large proportion of the mineral constituents of cocoa are dissolved by directly treating it with cold water. Wanklyn obtained in this way from genuine cocoa-nibs 6·76 per cent. organic matter, and 2·16 per cent. ash, the latter chiefly consisting of phosphates; a commercial cocoa gave, extract, 46·04 per cent.; ash, 1·04 per cent. The most common admixtures of cocoa and chocolate, are sugar and the various starches. The addition of foreign fats, chicory, and iron ochres, is also sometimes practised. Since prepared cocoas are generally understood to contain the first-named diluents, their presence can hardly be considered an adulteration, if the fact is mentioned upon the packages. Many varieties of the cocoas of commerce will be found to be deficient in cocoa-butter, a considerable proportion of which has been removed in the process of manufacture. This practice is also claimed to be justifiable, the object being to produce an article unobjectionable to invalids, which is not always the case with pure cocoa. In the analysis of cocoa the following estimations are usually made:—

Theobromine.—10 grammes of the sample are first repeatedly exhausted with petroleum-naphtha. The insoluble residue is mixed with a small quantity of paste, prepared by triturating calcined magnesia with a little water, and the mixture evaporated to dryness at a gentle heat. The second residue is boiled with alcohol and the alcoholic solution of theobromine filtered and evaporated to dryness in a tared capsule. It is then purified by washing with petroleum-naphtha and weighed. Bell has verified the existence in cocoa of a second alkaloid, distinct from theobromine, which crystallises in silky needles very similar to theine.

Fat.—The proportion of fat is readily determined by evaporating to dryness the petroleum-naphtha used in the preceding estimation. As already stated, it is generally present in a proportion of 50 per cent. in pure cocoa; the amount contained in prepared soluble cocoas being often less than 25 per cent. The English minimum standard is 20 per cent.

Ash.—The ash is determined by the incineration of a weighed portion of the sample in a platinum dish. In prepared cocoas and chocolates, the proportion of ash is considerably lower than in pure cocoa. It is of importance to ascertain the amount of ash soluble in water (the proportion in genuine cocoa is about 50 per cent.), and especially the quantity of phosphoric acid contained. Assuming that prepared cocoa contains 1·5 per cent. of ash, of which 0·6 per cent. consists of phosphoric acid, and allowing that pure cocoa contains 0·9 per cent. of phosphoric acid, Blyth adopts the following formula for calculating the proportion of cocoa present in the article:—

·6 × 100 ·9 = 66·66 per cent.

Starch.—A convenient method for estimating the starch is to first remove the fatty matter of the cocoa by exhaustion with petroleum-naphtha, and then boil the residue with alcohol. The remaining insoluble matter is dried, and afterwards boiled until the starch becomes soluble. It is next again boiled for several hours with a little dilute sulphuric acid, after which the solution is purified by addition of basic plumbic acetate. The liquid is then treated with sulphuretted hydrogen, in order to remove the lead, and the sugar contained in the filtered solution is determined by means of Fehling’s solution, and calculated to terms of starch. The proportion of starch normally present in cocoa is to be deducted from the results thus afforded. The variety of starch contained in cocoa differs in its microscopic appearance from the starches most frequently added.

Sugar.—The sugar may be determined by evaporating the alcoholic solution obtained in the preceding process, and then subjecting the residue to the same method of procedure.

The proportion of woody fibre in cocoa can be approximately estimated by the method of Henneberg and Stohman,[17] which consists in extracting the fat with benzole, boiling the remaining substances for half an hour, first with 1·25 per cent. sulphuric acid, then with 1·25 per cent. solution of potassium hydroxide. The residue is washed with alcohol and with ether, and its weight determined. Unwashed cocoa-berries, when treated in this manner, gave from 2 to 3 per cent. of cellulose, while cocoa husks furnished from 10 to 16 per cent. The presence of chicory in soluble cocoa and chocolate is easily recognised by the dark colour of the extract obtained, upon digesting the suspected sample with cold water; ochres and other colouring matters are detected by the reddish colour of the ash as well as by its abnormal composition. The addition of foreign fats to chocolates is stated to be occasionally resorted to.

The melting point of pure cocoa-butter varies from 30° to 33°. The identification of foreign fats can sometimes be accomplished by means of their higher melting point, and by an examination of the separated fat, according to Koettstorfer’s method (see p. 71). The table following gives the melting points of various fats, and the number of milligrammes of K(OH) required for the saponification of one gramme of the same.

Other tests have also been suggested for the detection of foreign fats in cocoa-butter:—

(a) Treat the fat with two parts of cold ether; pure cocoa-butter dissolves, forming a clear solution, whereas in presence of tallow or wax a cloudy mixture is obtained.

(b) Dissolve 10 grammes of the suspected fat in benzole, and expose the solution to a temperature of 0°. By this treatment a separation of pure cocoa-butter in minute grains is produced. The liquid is now heated to 14°·4, when the cocoa-fat will re-dissolve to a transparent solution, while the presence of tallow will be recognised by the turbid appearance of the liquid.