Fermentation and Taste of the Lees—Yeasty Flavor.—By the term fermentation in this connection we mean the malady which is known in different parts of France by various names, such as la pousse, vins montés, tournés, tarés, à l’échaud. It generally attacks those wines which are grown in low places, which come from poor varieties of grapes, or are produced in bad seasons, are weak, full of ferments, and thereby liable to work.
Mr. Boireau gives it the name of goût de travail, working taste, or fermentation flavor. He says that the taste is due to the presence of carbonic acid, disengaged during secondary alcoholic fermentation, by reason of saccharine matter contained in the wine, or of mucilaginous matters which give them their mellowness. The principal cause of fermentation is the presence of these matters joined with ferments, and takes place in an elevated temperature.
The yeasty flavor comes from the mixture in the wine of the lees and deposits already precipitated, and which are again brought into suspension by the movement of fermentation.
How Prevented.—Fermentation and the consequent taste of the lees are prevented by making and fermenting the wines under proper conditions, keeping them in an even temperature, and by separating them from their lees by well-timed rackings, as detailed in the chapters on General Treatment, Racking, etc.
Treatment.—The working is stopped by racking the wines into sulphured casks, and placing them in cellars of a cool and even temperature. (See [Sulphuring], etc.) If they have become turbid, they must be fined, and they must be left on the finings only as long as is strictly necessary for their clarification.
Machard recommends that about a quart of alcohol for 100 gallons of wine, or its equivalent of old brandy, be introduced into the sulphured cask before drawing the wine into it, and that it be fined in all cases.
Degeneration—Putrid Fermentation.—We are warned of degeneration in wines a long time in advance, in divers manners: by the loss of their fruity flavor, by bitterness, acrity, etc.; but the true symptoms in old wine are, the more abundant precipitation of their blue coloring matter, a heavy and tawny aspect, with a slightly putrid flavor. The principal causes are the same as those mentioned in speaking of the putrid decomposition in new wines, that is, feebleness in alcohol, and lack of tannin.
We know that by the time the tannin is transformed into gallic acid, the alcohol is diminished by slow evaporation, and it follows that wines which are too old have lost a part of those principles which give them their keeping qualities, alcohol and tannin.
The Duration of Different Wines is exceedingly unequal, and, like animate beings, they display marked differences in constitution. There are very feeble wines, as we have already seen, which are in the way of degeneration the first year, while others, firm and full-bodied, gain in quality for four, six, ten, and more years. As soon as it is seen that a wine, by its taste and appearance, has commenced to degenerate, it is important to arrest the degeneration at once.
Treatment.—Degeneration may be retarded by adding tannin, but it is preferable, in most cases, to mix the wine with younger wines of the same nature, firm, full-bodied, which are improving, and consequently possess an excess of those qualities which are wanting in the degenerating wine. (See [Wine in Bottles].)