Aging by Heat.—On the other hand, if we wish to hasten the maturity of our wines, we can do so by keeping them in a warm place rather than in a cool cellar. The younger the wines, and the more sugar and alcohol they contain, the more they will gain, and the less risk will they run if subjected to a temperature of from 60° to 86° F. For example, sweet wines which are only ripe at thirty or forty years will mature in fifteen or twenty years, at 68° of heat, and in five or ten years, at 86°; a Bordeaux or a Hermitage wine which at 50° would be made in eight or ten years, would certainly be made in four or five years at from 59° to 68°, and in two or three years at 77° or 86° of heat. He says that a temperature between 40° and 90° C. (104° and 194° F.) will disorganize many kinds of wine, particularly red wines and those which have remained long in the fermenting vat, though it will not have that effect upon all wines.
It is well known that the inhabitants of many southern countries are accustomed to expose their wines to a considerable degree of heat to hasten their maturity, and different methods are employed for the purpose, and it is important to know what kind of wine will be improved and what injured by the practice. On this subject Boireau says, that after many experiments, he can affirm that if the heat exceeds 30° C. (86° F.), it is injurious to the grand mellow wines of the Gironde; also to wines of a delicate bouquet whose alcoholic strength does not exceed 12 per cent. Fine wines which possess both an aromatic taste and bouquet, a fruity flavor, and a pronounced mellowness, by heat take on a certain tawny flavor of worn out wine; but they become dry, lose their mellowness, and coolness, and acquire a cooked flavor, which changes their nature and gives them an analogy with the wines of the south of France. This taste covers their natural flavor and renders them common.
He goes on to say that wines subjected to the action of heat in direct contact with the air, loss by evaporation a part of their alcohol; the oxygen deprives them of a part of their color, and if the influence is prolonged, they become weak and greatly deteriorated. Exposed to heat in imperfectly closed vessels, they deposit, and take the tawny flavor (goût de rancio) if their alcoholic strength exceeds 16 per cent.; but if feeble in spirit, and they remain long in this condition, the oxygen transforms a part of their alcohol into vinegar. In receptacles kept full and well stopped, they undergo but few constitutional changes, if the heat does not exceed 158° F.; but, nevertheless, a small part of their coloring matter is precipitated, and their taste is sensibly changed. A flavor of cooked wine is found, and a slight odor of the lees, no matter how quick the heating.
Whatever the kind of wine operated upon, care must be taken not to carry the heat too high, for it will decompose and precipitate certain principles in dissolution in the wine, and change its natural flavor. After cooling, voluminous deposits will be found, and the cooking will give the wine a disagreeable flavor and an odor of the residue of a still. The extreme limits of from 113° to 158° F. should not be exceeded, and the greater the heat the shorter should be the exposure to it.
Generally speaking, the wines which gain the most by heating, either by artificial means or by leaving them in casks well bunged, but in ullage, in warm store rooms, are strongly fortified liqueur wines. And in order that they be not injured under those conditions, they should contain at least 18 per cent. of pure alcohol. And as they will gradually lose a little of their spirit by evaporation, their alcoholic strength should be taken from time to time, and they should be kept up to the indicated degree by fortifying.
Preserving Wine by Heat.—Aside from the question of aging wine by the effect of heat, Pasteur has attempted to show that wines can be kept without change, if the temperature is raised for a short time to 130° or 140° F. This is on the theory that wines become flat, pricked, turned, or rotten, owing to secondary fermentations, and that each change is due to the action of a particular ferment, as stated in the chapter on fermentation; and that this degree of heat destroys the action of these ferments—in fact, kills them. It is owing to the presence of the alcohol, that they are destroyed by this degree of heat, for a must which has been raised to the boiling point still ferments according to the experience of Boireau and of Pellicot. The first named gives the results of his experiments in heating wines according to Pasteur’s plan. The wine was in bottles, and the heat was gradually raised to 52° C. (125.6° F.) In comparing the wines treated with unheated wines kept under the same conditions, he found that the wine which had been heated could support contact with the air with less injury than the unheated, but that nevertheless it became flat, covered with flowers, and acidified even in closed vessels which were not completely full; also that fine wines generally are injured by the process. The wines experimented upon had from 10 to 10½ per cent. of alcohol.
It is a costly process to subject wine to a high artificial heat, and owing to the doubt which yet seems to attend the matter, but few are likely to go to the expense.
Influence of Cold.—Most authors have something to say on the subject of congealed wines, and undoubtedly the liquid may be concentrated by freezing a portion of the water, and drawing off the remaining liquid. Those living in cold countries can try the experiment, but it will certainly not be practiced in California.
Mr. Boireau says that the liquid remaining acquires a flavor similar to that possessed by wines which have been heated; that fine wines of a delicate bouquet and flavor acquire a commoner flavor than those in their normal state.
Treatment of Frozen Wines.—It may not be amiss to indicate what treatment a wine should receive in case it has been frozen and has thawed again. It becomes turbid, loses part of its color, and several matters are precipitated, or remain in suspension, and it is liable to ferment when the temperature rises. The last named author says that it should be put in a place of even temperature, and if necessary, it should be fined; in which case it should be fortified with a strong wine of the same nature, or a small amount of brandy.