SECTION IX.
OF ARTIFICIAL FERMENTATION.
By what has been said, it appears, that, though fermentation is brought on by uniform causes, and productive of similar effects, it is subject to many varieties, both in respect to its circumstances and to its perfection. One difference is obvious, and seems to deserve our attention, as it furnishes a useful division between natural and artificial fermentation. The first rises spontaneously, and requires nothing to answer all the necessary purposes, but the perfection of the juices, and the advantage of a proper heat. The other, at first sight less perfect, wants the assistance of ferments, or substitutes, without which the act could, either not at all, or very imperfectly, be excited.
There are undoubtedly liquors, which, though they have of themselves a tendency to fermentation, and are naturally brought to it, yet, from some defect in the proportions of their constituent parts, either do not acquire a proper transparency, or cannot maintain themselves in a sound state for a sufficient time. These disadvantages, inbred with them, can hardly ever be entirely removed; they gain very little, especially the latter, from age, and therefore are really inferior to liquors, which require the assistance of substituted ferments, to become real wines. In some artificial fermentations, the ferments are so duly and properly supplied, and so intimately blended with the liquor, that in the end they approach very near to, and even vie with, the most perfect natural wines. Were I to enter into a more minute detail, it might be shewn, that wines, when transported from a hot climate to a cold one, are often hurt and checked in the progress of the repeated frettings they require; from whence they become or remain imperfect, unless racked off from their grosser lees, or precipitated with strong menstruums; whereas beers may be so brewed, as to be adapted either to a hot or a cold region, not only without any disadvantage, but with considerable improvements.
Hitherto I have considered grapes as a most pulpous fruit, sufficient to furnish the quantity of water necessary for extracting its other parts; but the natives of the countries where this fruit abounds, in order to preserve them, as near as possible in their primitive state, after they are gathered, suspend them in barns, or place them in ovens, to dry. Thus, being in great measure divested of their aqueous parts, these grapes remain almost inactive, and without juices sufficient to form wines.
In all bodies, the various proportions of their constituent parts produce different effects; hence they remain more or less in a durable state, and tend either to inaction, fermentation, or putrefaction. Now, by a judicious substitution of such parts as shall be wanting, they are nearly, if not wholly, restored to their pristine nature, as may be proved by the observations and experiments communicated to the public by Dr. Pringle. Thus grapes, though dried and exported from their natural climate to another, by the addition of water only, ferment spontaneously, and form wines very near alike to such as they would have produced before. It may, with confidence, be said, that, when any considerable difference appears, it arises from the injudicious manner in which the water is administered, from the fruit not being duly macerated, or from want of such heat being conveyed to the water and fruit, as the juices would have had, if they had been expressed out of the grapes when just gathered; often from the whimsical mixture of other bodies therewith, and perhaps too from the quantity of brandy, which is always put to wines abroad, to prevent their fretting on board a ship. Upon the whole, though, from what just now has been observed, some small difference must take place, it rather proves than contradicts the fact, that, a due quantity of water being applied to dry raisins, an extract may be formed, which will be impregnated with all the necessary constituent parts the grapes had in them when ripe upon the vine, consequently will spontaneously ferment, and make a vinous liquor. Water then, in this case, becomes a substitute, and the liquors produced in this manner may be accounted of the first class of artificial wines.
Vegetables, in their original state, are divisible into the pulpous and farinaceous kinds, both possessing the same constituent parts, though in different proportions. If from the farinaceous such parts be taken away as they superabound in, and others be added, of which they are defective, these vegetables may, by such means, be brought to resemble, in the proportion of their parts, more especially in their musts, the natural wines I have before been treating of: and these being universally acknowledged to be the standard of wines, the nearer any fermented liquor approaches thereto, by its lightness, transparency, and taste, the greater must its perfection be.
To enquire which of the pulpous or which of the farinaceous kinds of vegetables are fittest for the purpose of wine-making, would here be an unnecessary digression. Experience, the best guide, hath, on the one side, given the preference to the fruit of the vine, and on the other to barley. To make a vinous liquor from barley, having all the properties of that produced from the grape, is a task, which can only be compassed by rendering the wort of these, similar to the must of the other.
As malt liquors require the addition of other substitutes, besides water, to, become perfect wines, they can only be ranked in the second class of artificial fermentation. These substitutes are properly called ferments, and merit the brewer’s closest attention.
Ferments, in general, such as yeast, flowers or lees of wine, honey, the expressed juices of ripe fruits, are subjects more or less replete with elastic air, and convey the same to musts, which stand in need thereof. Boerhaave has ranged these, and several others, in different classes, according to their different powers, or rather in proportion to the quantity of air they contain for this purpose.
The juice of the grape, when fermented, forms more lees than the extracts of malt. May we not, from thence, infer that, in the fruit, the elastic air is both more abundant, and contained in a greater number of stronger, though smaller, vesicles, than it is in the malt? The barley, being first saturated with water, germinated only, and then dried with a heat far exceeding that which ripened it, or that which fermentation admits of, has its air in part driven out. The expulsion of air from the worts of beers and ales is still farther effected by the long boiling they undergo. Hence the necessity of replacing the lost elastic air, in order that these extracts may become fermentable. This is effected by means of the yeast, which, consisting of a collection of small bubbles, filled with air, and ready to burst by a sufficient heat, becomes the ferment, which facilitates the change of the wort into a vinous liquor.