Acrity.—An acrid taste, with which certain wines are affected as they grow old, is a sign of degeneration. Mr. Boireau says that he has reason to believe that this disease is due to the presence of acetic acid, coupled with the precipitation of the mucilages which give the mellow flavor to wine. It is more often observed in old, dry wine, improperly cared for, and consequently deprived of its fruity flavor.
The Proper Treatment is to remove the acetic acid by using a gramme or two per litre (60 to 120 grains to a gallon) of carbonate of magnesium. (See [Sourness], [Pricked Wines].) If the acrity is not too great, wines may be fortified, or mixed with a strong, young, clean-tasting wine of the same nature, after which they should be fined.
Bitterness, which is often a natural defect (which has already been considered), becomes an accidental defect when developed in old wines which were previously sound. It is almost always a commencement of degeneration. This bitter taste comes principally from those combinations which are formed by the dissolution of the coloring matter, and by the precipitation of the mucilaginous substances, the pectines, which give the wine unctuosity and its fruity flavor.
Treatment.—The way to diminish this bitterness is to fortify and regenerate the bitter wine which has entered on its decline, by mixing it with wine of the same nature, but young, stout, and full-bodied, and which have not yet reached maturity. The mixture should be fined with albumen, and racked after resting a fortnight. The wine may be improved in this way, but the bitterness will reappear in a few months. It should, therefore, be used as soon as possible.
Machard recommends the following: Fine the wine with eggs, and let it rest till clear. Burn in a clean cask a quarter or a half of a sulphur match (for 60 gallons), and pour in the bitter wine at once with the smoke in the cask, after having added to each litre of the wine about one gramme of tartaric acid (say 60 grains to the gallon), dissolved in warm water. It must then be mixed with from a fourth to a half of old wine, firm and well preserved. He says that a new wine to mix with it is not suitable, not having sufficient affinity for the old.
Where there is such a difference of opinion as there is between these two authors, one recommending the mixture of new wine, and the other forbidding it, every one had better experiment for himself with a small quantity, and after the cut wines have become thoroughly amalgamated, a choice can be made.
And yet, Mr. Machard says that if the bitterness is not very great, it is better to give them no other treatment than simply mixing them with younger ones, but which have a tendency to become sour, or are already slightly pricked.
Mr. Maumene Distinguishes Two Kinds of Bitterness: 1. The nitrogenous matters, under certain circumstances not well understood, appear to be changed into a bitter product, and entirely spoil the best wine. This effect depends especially upon the elevation of the temperature and the old age of the wine. He says that he knows of but one way to remove this bitterness, and that is to add a small quantity of lime. For example, 25 to 50 centigrammes per litre (say 15 to 30 grains per gallon). The lime should be perfectly new and fresh. It is slacked in a little water or wine, and poured into the cask; after stirring well, it is left to rest for two or three days, and then racked and fined. Probably the lime combines with the nitrogenous matters, gives an insoluble compound, which separates from the wine, and restores to it its former flavor. The wine ought to remain acid after this treatment. He says that it has succeeded with him a great number of times. 2. Another cause of bitterness appears to him to be the formation of the brown resin of ammoniacal aldehyde, under the influence of oxygen. The ferment which adheres to the inside of the cask gives a little ammonia by decomposition.
We see how the wine, under the influence of the air, produces a little aldehyde, the ammoniacal aldehyde, and finally the very bitter brown resin, whose formation was made known by Liebig. It is under these circumstances that sulphuring may be employed as a remedy. The sulphurous acid destroys the resinous matter in taking its oxygen to become sulphuric. There is then made sulphate of ammonia and pure aldehyde. These two substances by no means communicate to the wine the disagreeable flavor of the brown resin from which they are derived.
Another origin of bitterness is given, that of the oxidation of the coloring matter, but there is no positive proof of this any more than there is of the two causes mentioned by him. Unfortunately, the whole matter is hypothetical.