I am sensible these facts had been represented in a more natural light, had I observed the degrees of heat impressed on the vine in every season of the year; the difference of the sun’s heat, in every hour of the day, a variety exceeding that in the shade; that between night and day; the aspect of the plant; the heat of the earth at its surface, as well as at the roots of the vine; all these would have increased the circumstances to a prodigious extent; which, though perhaps requisite to satisfy philosophic investigation, might, from their number and variety, have been the means rather to induce us to error, than to discover the general rules by which nature acts.
From the above-related process we are taught, that nature, in forming wines, is not confined to a certain fixed number of degrees, but admits, for this act, of a considerable latitude, according to the extent of which the wines vary in taste and properties; and that she affects an equality of heat in each period of vegetation; from whence the brewer is taught, if he form his malt-liquors with four mashes, as in the autumn and spring the vine is impressed with heats nearly uniform, so ought his two first mashes to be; the third, in imitation of the high heat of summer, should be much hotter, and the heat of his last mash the same with this; and this general rule has been found universally true, for beers expected to preserve themselves sound a sufficient time; and admits but of a proportional variation, when fewer or more mashes are employed, as the degrees of heat denominating the constituent parts of the grain, must be applied in proportion to the quantity of water used to each mash; but in malt liquors speedily to be drank, or when we deviate greatly from the more perfect productions of nature, we are then compelled to swerve from her rules; a practice never profitable, and which nothing but necessity can justify.
The nature of the soil proper for the vine, might, in another work, be a very useful enquiry. It will be sufficient here, barely to hint at the effect, which lixivial soils produce in musts. The Portugueze, when they discovered the Island of Madeira in 1420, set fire to the forests, with which it was totally covered. It continued to burn for the space of seven years, after which the land was found extremely fruitful, and yielding such wines, as, at present, we have from thence, though in greater plenty. It is very difficult to fine these wines, and, though the climate of this island is more temperate than that of the Canaries, the wines are obliged to be carried to the Indies and the warmer parts of the globe, to be purged, shook, and attenuated, before they can arrive to an equal degree of fineness with other wines; were the Portugueze acquainted with what may be termed the artificial method of exciting periodical fermentation, much or the whole of this trouble might be avoided. Hence we see, that soils impregnated with alkaline salts will produce musts able to support themselves longer, and to resist acidity more, than other soils, under the same degree of heat.
Grapes have the same constituent parts as other vegetables. The difference between them, as to their tastes and properties, consists in the parts being mixed in different proportions. This arises, either from their absorbent vessels more readily attracting some juices than others, or from their preparing them otherwise, under different heats and in different soils.
We find, says Dr. Hales, by the chymical analysis of vegetables, that their substance is composed of sulphur, volatile salts, water, and earth, which principles are endued with mutual attracting powers. There enters likewise in the composition, a large portion of air, which has a wonderful property of attracting in a fixed, or of repelling in an elastic state, with a power superior to vast compressing forces. It is by the infinite combinations, actions, and reactions of these principles, that all the operations in animal and vegetable bodies are effected.—Boerhaave, who is somewhat more particular with regard to the constituent parts of vegetables, says, that they contain an oil mixed with a salt in form of a sapo, and that a saponaceous juice arises from the mixture of water with the former.
Thus we see, from the composition of grapes, that they have all the necessary principles to form a most exquisite liquor, capable, by a gentle heat, to be greatly attenuated. They abound with elastic air, water, oils, acid, and neutral salts, and even saponaceous juices.—The air contained in the interstices of fluids is more in quantity than is commonly apprehended. Sir Isaac Newton has proved that water has forty times more pores than solid parts; and the proportion, likely, is not very different in vegetable juices. When the fruit is in its natural entire state, the viscidity of the juices, and their being enveloped by an outward skin, prevent the expansion of the inclosed air; it lies as it were inactive. In this forced state, it causes no visible motion, nor are the principles, thus confined, either subjected to any apparent impressions of the external atmosphere, or so intimately blended as when they are expressed. A free communication of the external air, with that contained in the interstices of the liquor, is required to form a perfect mixture. By what means this is effected, what alterations it produces, or, in general, in what manner the juice of the grape becomes wines, must be the subject of our next inquiry.
The process of a perfect fermentation is undoubtedly the same (where the due proportions of the constituent parts, forming the must, are exactly kept) whatever vegetable juices it is excited in. For this reason, we will observe the progress of this act in beers and ales, these being subjects we are more accustomed to, and where the characters appear more distinct, in order to apply what may be learned from thence to our chief object, the business of the brewer.