Changes during Fermentation.

No entirely satisfactory theory of the changes in cacao due to fermentation has yet been established. It is known that the sugary pulp outside the beans ferments in a similar way to other fruit pulp, save that for a yeast fermentation the temperature rises unusually high (in three days to 47 degrees C.), and also that there are parallel and more important changes in the interior of the bean. The difficulty of establishing a complete theory of fermentation of cacao has not daunted the scientists, for they know that the roses of philosophy are gathered by just those who can grasp the thorniest problems. Success, however, is so far only partial, as can be seen by consulting the best introduction on the subject, the admirable collection of essays on The Fermentation of Cacao, edited by H. Hamel Smith. Here the reader will find the valuable contributions of Fickendey, Loew, Nicholls, Preyer, Schulte im Hofe, and Sack.

The obvious changes which occur in the breaking down of the fruity exterior of the bean should be carefully distinguished from the subtle changes in the bean itself. Let us consider them separately:—

(a) Changes in the Pulp.—Just as grape-pulp ferments and changes to wine, and just as weak wine if left exposed becomes sour; so the fruity sugary pulp outside the cacao bean on exposure gives off bubbles of carbon dioxide, becomes alcoholic, and later becomes acid. The acid produced is generally the pleasant vinegar acid (acetic acid), but under some circumstances it may be lactic acid, or the rancid-smelling butyric acid. Kismet! The planter trusts to nature to provide the right kind of fermentation. This fermentation is set up and carried on by the minute organisms (yeasts, bacteria, etc.), which chance to fall on the beans from the air or come from the sides of the receptacle. One yeast-cell does not make a fermentation, and as no yeast is added a day is wasted whilst any yeasts which happen to be present are multiplying to an army large enough to produce a visible effect on the pulp. Any organism which happens to be on the pod, in the air, or on the inside of the fermentary will multiply in the pulp, if the pulp contains suitable nourishment. Each kind of organism produces its own characteristic changes. It would thus appear a miracle if the same substances were always produced. Yet, just as grape-juice left exposed to every micro-organism of the air, generally changes in the direction of wine more or less good, so the pulp of cacao tends, broadly speaking, to ferment in one way. It would, however, be a serious error to assume that exactly the same kind of fermentation takes place in any two fermentaries in the world, and the maximum variation must be considerable. As the pulp ferments, it is destroyed; it gradually changes from white to brown, and a liquid ("sweatings") flows away from it. The "sweatings" taste like sweet cider. At present this is allowed to run away through holes in the bottom of the box, and no care is taken to preserve what may yet become a valuable by-product. I found by experiment that in the preparation of one cwt. of dry beans about 1-1/2 gallons of this unstable liquid are produced. In other words, some seven or eight million gallons of "sweatings" run to waste every year. In most cases only small quantities are produced in one place at one time. This, and the lack of knowledge of scientifically controlled fermentation, and the difficulty of bottling, prevent the starting of an industry producing either a new drink or a vinegar. The cacao juice or "sweatings" contains about fifteen per cent. of solids, about half of which consists of sugars. If the fermentation of the cacao were centralised in the various districts, and conducted on a large scale under a chemist's control, the sugars could be obtained, or an alcoholic liquid or a vinegar could easily be prepared.

The planter decides when the beans are fermented by simply looking at them; he judges their condition by the colour of the pulp. When they are ready to be removed from the fermentary they are plump, and brown without, and juicy within.

(b) Changes in the Interior of the Bean.—What is the relation between the comparatively simple fermentation of the pulp and the changes in the interior of the bean? This important question has not yet been answered, although a number of attempts have been made.

As far as is known, the living ferments (micro-organisms) do not penetrate the skin of the bean, so that any fermentation which takes place must be promoted by unorganised ferments (or enzymes). Mr. H.C. Brill[2] found raffinase, invertase, casease and protease in the pulp; oxidase, raffinase, casease and emulsinlike enzymes in the fresh bean; and all these six, together with diastase, in the fermented bean. Dr. 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."

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:

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.

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