Part 5 (1/2)

Fickendey says: ”The object of fermentation is, in the main, to kill the germ of the bean in such a manner that the efficiency of the unorganised ferment is in no way impaired.”

[2] _Philippine Journal of Science_, 1917.

From my own observations I believe that forastero beans are killed at 47 degrees C. (which is commonly reached when they have been fermenting 60 hours), for a remarkable change takes place at this temperature and time. Whilst the micro-organisms remain outside, the juice of the pulp appears to penetrate not only the skin, but the flesh of the bean, and the brilliant violet in the isolated pigment cells becomes diffused more or less evenly throughout the entire bean, including the ”germ.” It is certain that the bean absorbs liquid from the outside, for it becomes so plump that its skin is stretched to the utmost. The following changes occur:

(1) _Taste._ An astringent colourless substance (a tannin or a body possessing many properties of a tannin) changes to a tasteless brown substance. The bean begins to taste less astringent as the ”tannin” is destroyed. With white (criollo) beans this change is sufficiently advanced in two days, but with purple (forastero) beans it may take seven days.

(2) _Colour._ The change in the tannin results in the white (criollo) beans becoming brown and the purple (forastero) beans becoming tinged with brown. The action resembles the browning of a freshly-cut apple, and has been shown to be due to oxygen (activated by an oxidase, a ferment encouraging combination with oxygen) acting on the astringent colourless substance, which, like the photographic developer, pyrogallic acid, becomes brown on oxidation.

(3) _Aroma._ A notable change is that substances are created within the bean, which _on roasting_ produce the fine aromatic odour characteristic of cocoa and chocolate, and which Messrs. Bainbridge and Davies have shown is due to a trace (0.001 per cent.) of an essential oil over half of which consists of linalool.[3]

(4) _Stimulating Effect._ It is commonly stated that during fermentation there is generated theobromine, the alkaloid which gives cacao its stimulating properties, but the estimation of theobromine in fermented and unfermented beans does not support this.

(5) _Consistency._ Fermented beans become crisp on drying.

This development may be due to the ”tannins” encountering, in their dispersion through the bean, proteins, which are thus converted into bodies which are brittle solids on drying (compare tanning of hides). The ”hide” of the bean may be similarly ”tanned”--the sh.e.l.l certainly becomes leathery (unless washed)--but a far more probable explanation, in both cases, is that the gummy bodies in bean and sh.e.l.l set hard on drying.

[3] _Journal of the Chemical Society_, 1912.

We see, then, that although fermentation was probably originally followed as the best method of getting rid of the pulp, it has other effects which are entirely good. It enables the planter to produce a drier bean, and one which has, when roasted, a finer flavour, colour, and aroma, than the unfermented. Fermentation is generally considered to produce so many desirable results that M. Perrot's suggestion[4] of removing the pulp by treatment with alkali, and thus avoiding fermentation, has not been enthusiastically received.

[4] _Comptes Rendus_, 1913.

Beans which have been dried direct and those which have been fermented may be distinguished as follows:

CACAO BEANS

DRIED DIRECT. FERMENTED AND DRIED.

_Shape of bean_ Flat Plumper _Sh.e.l.l_ Soft and close fitting Crisp and more or less free.

_Interior: colour_ Slate-blue or mud-brown Bright browns and purples ” _consistence_ Leather to cheese Crisp ” _appearance_ Solid Open-grained ” _taste_ More or less bitter Less astringent or astringent

Whilst several effects of fermentation have not been satisfactorily accounted for, I think all are agreed that to obtain one of the chief effects of fermentation, namely the brown colour, oxidation is necessary. All recognise that for this oxidation the presence of three substances is essential:

(1) The tannin to be oxidised.

(2) Oxygen.

(3) An enzyme which encourages the oxidation.

All these occur in the cacao bean as it comes from the pod, but why oxidation occurs so much better in a fermented bean than in a bean which is simply dried is not very clear. If you cut an apple it goes brown owing to the action of oxygen absorbed from the air, but as long as the apple is uncut and unbruised it remains white. If you take a cacao bean from the pod and cut it, the exposed surface goes brown, but if you ferment the bean the whole of it gradually goes brown without being cut.

My observations lead me to believe that the bean does not become oxidised until it is killed, that is, until it is no longer capable of germination. It can be killed by raising the temperature, by fermentation or otherwise, or as Dr. Fickendey has shown, by cooling to almost freezing temperatures. It may be that killing the bean makes its skin and cell walls more permeable to oxygen, but my theory is that when the bean is killed disintegration or weakening of the cell walls, etc., occurs, and, as a result, the enzyme and tannin, _hitherto separate_, become mixed, and hence able actively to absorb oxygen. The action of oxygen on the tannin also accounts for the loss of astringency on fermentation, and it may be well to point out that fermentation increases the internal surface of the bean exposed to air and oxygen.

The bean, during fermentation, actually sucks in liquid from the surrounding pulp and becomes plumper and fuller. On drying, however, the skin, which has been expanded to its utmost, wrinkles up as the interior contracts and no longer fits tightly to the bean, and the cotyledons having been thrust apart by the liquid, no longer hold together so closely. This accounts for the open appearance of a fermented bean. As on drying large inters.p.a.ces are produced, these allow the air to circulate more freely and expose a greater surface of the bean to the action of oxygen. Since the liquids in all living matter presumably contain some dissolved oxygen, the problem is to account for the fact that the tannin in the unfermented bean remains unoxidised, whilst that in the fermented bean is easily oxidised. The above affords a partial explanation, and seems fairly satisfactory when taken with my previous suggestion, namely, that during fermentation the bean is rendered pervious to water, which, on distributing itself throughout the bean, dissolves the isolated ma.s.ses of tannin and diffuses it evenly, so that it encounters and becomes mixed with the enzymes. From this it will be evident that the major part of the oxidation of the tannin occurs during drying, and hence the importance of this, both from the point of view of the keeping properties of the cacao, and its colour, taste and aroma.

It will be realised from the above that there is still a vast amount of work to be done before the chemist will be in a position to obtain the more desirable aromas and flavours. Having found the necessary conditions, scientifically trained overseers will be required to produce them, and for this they will need to have under their direction arrangements for fermentation designed on correct principles and allowing some degree of control. Whilst improvements are always possible in the approach to perfection, it must be admitted that, considering the means at their disposal, the planters produce a remarkably fine product.

[Ill.u.s.tration: FOR DRYING SMALL QUANt.i.tIES.