Food Adulteration and Its Detection. Jesse P. Battershall
acid
Blyth gives the annexed table, showing the characteristic differences between coffee and chicory ash:[13]—
| Coffee Ash. | Chicory Ash. | |
| per cent. | per cent. | |
| Silica and sand | none | 10·69 to 35·88 |
| Carbonic acid | 14·92 | 1·78 „ 3·19 |
| Ferric oxide | 0·44 to 0·98 | 3·13 „ 5·32 |
| Chlorine | 0·26 „ 1·11 | 3·28 „ 4·93 |
| Phosphoric acid | 10·00 „ 11·00 | 5·00 „ 6·00 |
| Total soluble ash | 75·00 „ 85·00 | 21·00 „ 35·00 |
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:—
| Chicory. | Figs. | Acorns. | Rye. | |
| per cent. | per cent. | per cent. | per cent. | |
| Water | 12·16 | 18·98 | 12·85 | 15·22 |
| Nitrogenous substances | 6·09 | 4·25 | 6·13 | 11·84 |
| Fat | 2·05 | 2·83 | 4·61 | 3·46 |
| Sugar | 15·87 | 34·19 | 8·05 | 3·92 |
| Other non-nitrogenous substances. | 46·71 | 29·15 | 62· | 55·37 |
| Cellulose | 11·0 | 7·16 | 4·98 | 5·35 |
| Ash | 6·12 | 3·44 | 2·12 | 4·81 |
| Substances soluble in water | 63·05 | 73·8 | .. | 45·11 |
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:—
| Substances Soluble in Water. | Ready- formed Sugar. | Sugar after Inversion. | |
| per cent. | per cent. | per cent. | |
| Roasted coffee | 23·81 | 0·20 | 24·59 |
| „chicory | 65·42 | 23·40 | 22·14 |
| „rye | 31·92 | .. | 75·37 |
| „coffee + 10 per cent. chicory | 30·63 | 2·30 | 23·15 |
| „coffee + 10 per cent. rye | 25·98 | 0·19 | 29·60 |
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).