The Theory and Practice of Brewing

by Michael Combrune

Most grapes contain juices, which, when fermented, become in time as light and pellucid as water, and are possessed of fine spiritous parts, sufficient to cherish, comfort, and even inebriate. But these properties of vinosity are observed not to be equally perfect in the fruits of all vines; some of them are found less, others not at all proper for this purpose. It is therefore necessary to examine the circumstances which attend the forming and ripening of those grapes, whose juices produce the finest liquors of the kind.

All grapes, when they first bud forth, are austere and sour, therefore of a middle nature. And this can be no other than the effect of the autumnal remaining sap, mixed with the new raised vernal one, the consequence of which mixture will be found greatly to merit our inquiry. As far as our senses can judge, at first, it appears that the juice, in this state, consists of somewhat more than an acid combined with a tasteless water. When the fruit is ripe, it becomes full of a rich, sweet, and highly flavoured juice. The color, consistency, and taste of which shew, that, by the power of heat, a considerable quantity of oil has been raised, and, sheathing the salts, is the reason of its saccharine taste and saccharine properties.

In England, grapes are probably produced under the least heat they can be raised by. They discover themselves in their first shape, about June, when the medium heat of the twenty-four hour’s shade is 57,60. This, with what more should be added for the effect of the sun’s beams, are the degrees of heat which first introduce the juices into this fruit.

The highest degrees of heat, in the countries where grapes come to perfect maturity, have been observed to be, in various parts of Italy, Spain, and Greece 100, and at Montpelier 88, in the shade; to which, according to Dr. Lining’s observations, 20 degrees must be added for the effect of the sun’s beams. The greatest heat in Italy will then amount to 120 degrees, and in the south of France to 108. These approach nearly to the strongest heats observed in the hottest climates, which, in Astracan, Syria, Senegal, and Carolina, were from 124 to 126 degrees.

Those countries, where the heat is greatest, in general produce the richest fruits, that is, the most impregnated with sweet, thick and oily juices. We are told, among the Tockay wine-hills, there is one which, directly fronting the south, and being the most exposed to the sun, yields the sweetest and richest grapes. It is called the sugar-hill, and the delicious wines extracted from this particular spot, are all deposited in the cellars of the imperial family. Those grapes, some in the Canaries, some in other places, being suffered to remain the longest on the tree, with their stems half cut through, by this means procure their juices to be highly concentrated, and produce that species of sweet, oily, balmy wines, which, from this operation, are called sack, a derivation of the French word sec or dry.

In all distillations of unfermented vegetables, water and acid salts rise first. A more considerable degree of fire is required for the elevation of oils, and a still greater one for the lixivial salts, which render those oils miscible with water.

A plant, exposed to a very gentle heat, at first yields a water which contains the perfect smell of the vegetable blended with a subtile oil; if more heat be added, an heavier oil will come over: from some a volatile alkali, from others a phlegm will rise, which gradually grows acid; and, last of all, with the farther assistance of fire, the black, thick, empyreumatic sulphur. Nature, in a less degree, may be said to place a like series of events before our eyes, in the forming and maturating of grapes, and it is by imitating what she does, that the inhabitants of different countries may improve the advantages of their soil and of their air.

In order to illustrate the doctrine, that grapes are endued with various properties, in proportion to the heat of the air they have been exposed to, let us remember what Boerhaave has observed, that, in very hot weather, the oleous corpuscles of the earth are carried up into the air, and, descending again, cause the showers and dews in summer to be very different from the pure snow of winter. The first are acrid, and disposed to froth, the last is transparent and insipid. Hence summer rain, or rain falling in hot seasons, is always fruitful, whereas in cold weather it is scarcely so at all. In winter the air abounds with acid parts, neither smoothed by oils nor rarified by heat: cold is the condensing power, as heat is the opener of nature. In summer, the air, dilating itself, penetrates every where, and gives to the rain a disposition to froth, occasioned by the admixture of oleous and aërial particles. Thus the acid salts, either previously existing, or by the vernal heat introduced into the grapes, and necessary to their preservation, are neutralized by coming in contact with the juices the foregoing autumn produced; after which a hotter sun, covering or blending these juices with oils, changes the whole into a saccharine form. In proportion as these acids are more or less sharp, and counterbalanced by a greater or lesser quantity of oils, the juices of grapes approach more or less to the state of perfection, which fermentation requires.

There are many places, as Jamaica, Barbadoes, &c. in which experience shews the vine cannot be cultivated to advantage. By comparing the heat of these places with those in Italy and Montpelier, it appears this defect is not owing to excessive heats, but to their constancy and uniformity; the temperature of the air of these countries seldom being so low as the degree necessary for the first production of the fruit. Whenever the cultivation of the vine is attempted in these parts of the West Indies, the grapes, on their first appearance, are shaded and skreened from the beams of the sun, which, in their infancy, they are not able to bear.

Hence we learn, though nature employs both the autumnal and vernal seasons, yet there are lesser heats with which she prepares the first juice of grapes, a stronger power of the sun she requires to form the fruit, and a greater than either to ripen it. We have investigated the lowest degrees of heat, in which grapes are produced, and nearly the highest they ever receive to ripen them. Let us call the first the germinating degrees, and the last those of maturation. If nearly 58 be the lowest of the one, and 126 the highest of the other, and if a certain power of acids is necessary for the germination of the grapes, which must be counterbalanced by an equal power of oils raised by the heat of the sun for their maturation, then the medium of these two numbers, or 92, maybe said to be a degree at which this fruit cannot possibly be produced, and inferior to that by which it should be maturated. At Panama the lowest degree of heat in the shade is 72, to which 20 being added, for the sun’s beams, the sum will be 92, and consequently no grapes can grow there, except the vines be placed in the shade.