Temperature.—The temperature most favorable to fermentation—that is, at which it commences most promptly, and goes on the most rapidly—is between 77° and 95° F., and it does not cease until the temperature descends below 49°, or rises above 140°. If the temperature is favorable, fermentation ought to commence in ten or twelve hours from the time the pomace is put into the vat, or the juice into the barrel. In countries where the weather is cold at the wine making season, it is necessary that the grapes should be gathered in the heat of the day, or fermentation will be long in commencing; and if the weather continues unfavorable, so that the grapes do not become warmed by the sun, it is even necessary to heat a portion of the must artificially, and pour it into the vats or casks, or to raise the temperature of the fermenting house.
Mr. Maumené also recommends that the vats be surrounded with mats of loose straw, four or five inches thick, to be kept in place by a covering of linen cloth; and in this way the temperature produced by the fermentation may be maintained in cool weather, without resorting to fires in the fermenting house.
It is not necessary, however, that the temperature of the surrounding atmosphere should be as high as that indicated as most favorable to fermentation; for it commences readily in a temperature of about 70°, and the liquid will soon rise to 85° or 95°, by the heat developed during the process; and unless the surrounding temperature descends below 65°, this heat will be maintained, and the fermentation will not be checked. Dr. Guyot says, however, that, to make fine wines, it should be maintained at 68°, at least; and that, in other cases, it should not be allowed to fall below 60°.
Fermenting Houses.—It is important not only that fermentation should commence promptly, but that it should be maintained regularly; and although a great amount of heat is developed by fermentation, yet the must is liable to cool during the night and cold days, unless the vats and casks are protected from the change of temperature, whereby the fermentation may be checked, to the injury of the wine. The natural conclusion is that the must ought to be fermented in closed places. In California, however, it is not necessary to construct the fermenting house with the same care required in colder climates, where it is deemed desirable to furnish them with double windows and doors. It cannot be denied that good wine is made in this State, in places where the vats remain out of doors, shaded only by trees; but the practice is not to be encouraged, for the fermentation will be checked if the temperature of the surrounding atmosphere goes to 60° and below. In constructing a fermenting house, it ought to be so arranged, when practicable, as to be on a lower level than that of the stemmer and crusher, and higher than the cellar; for then the pomace and must can be run immediately into the vats and casks, and, after the first fermentation, the wine can be drawn off through a hose into the casks in the cellar, thereby saving time and labor.
CHAPTER VI.
RED WINE.
Red wines are made from colored grapes, and the color is extracted from the skins during fermentation. The coloring matter is blue, but is changed to red by the action of the acids in the must. (See [Coloring Matter]—[Oenocyanine].) In order to develop this color, the grapes are fermented, skins and juice together, and the press is only brought into requisition after the first fermentation is completed.
Fermenting Tanks or Vats.—The tanks or vats in which red wine is fermented, in France are generally made of oak, sometimes of masonry, but in this State redwood has been almost universally adopted, and I am not aware of any serious inconveniences from its use. It is advisable before using them the first time, to steam them for several hours, or thoroughly soak them to extract the coloring matter of the wood.
The capacity depends upon the quantity of wine to be made in a season, varying from 1000 gallons to 2500 gallons and more, and a sufficient number should be provided that when wine making has commenced, it can be carried on without interruption till the crop is worked up. The number of workmen must be considered as well as the amount of grapes, and everything ought to be so arranged that the fermentation will be finished in the first tank filled, by the time the last one is full, so that the first can be emptied and filled again, and then the second, and so on. A hole must be bored in each vat two or three inches from the bottom by which to draw the wine through a faucet. And some kind of a strainer must be put over this hole inside to keep back the marc—a piece of perforated tin, a grating of small sticks, or a bundle of straw or vine cuttings kept in place by a stone.
Filling the Tanks.—In order that the whole mass in one tank may be equally fermented, it should receive its full complement of grapes in one day. By putting in part of the grapes one day and part another, not only will some of them complete their fermentation before the others, but the addition of fresh grapes to the fermenting mass will interrupt the fermentation, and prove injurious to the wine. The vats must not be filled to their full capacity, for during violent fermentation the marc, consisting of skins and seeds, or those with the stems, rises to the top, brought up by the bubbles of carbonic acid which are constantly rising, and a portion of the boiling and foaming mass may be carried over the top, and much wine thereby be lost. They should only be filled to within a foot or a foot and a half of the top, and a little experience will show the proper practice. Guyot says that they should only be filled to five-sixths of their capacity at most. Another reason for not filling the tank is that a layer of carbonic acid gas will occupy the space left vacant by the pomace, and prevent the contact of the air and the consequent souring of the wine, by the changing of a portion of the alcohol into acetic acid—vinegar.
Red wine is fermented in open vats, vats loosely covered, or in vats hermetically sealed, and good wine is made in each way.