The Roughness Disappears in Time, because the tannin is transformed into gallic acid, and besides is precipitated by other principles contained in the wine, and by finings.
An Excess of Tannin is Avoided in strong, dark-colored, full-bodied wines by removing all the stems, and by early drawing from the tank. If the wines are inclined to be soft, weak, and with but little spirit, no attempt should be made to avoid roughness.
When wines are put into new casks, their roughness is increased by the tannin derived from the oak wood of which they are made; but during insensible fermentation a good deal of the tannin is thrown down with the vegetable albumen contained in the new wine.
How Removed.—If the wines are of good body and color, the roughness may be removed by fining them with a strong dose of gelatine, two or three ounces to 100 gallons. As this removes a portion of the color, it should only be resorted to in the case of rough and dark-colored wines, to hasten their maturity.
Bitterness and Taste of the Stems—Causes.—Bitterness is a disagreeable taste which, in new wines attacked by it, comes from the dissolution of a bitter principle contained in the stems, a principle entirely different from tannin. Sometimes it is communicated by the skins of certain varieties of grapes.
This is Prevented by allowing the grapes to reach complete maturity, and above all by stemming them all, and by not leaving the wine too long in the fermenting vat.
The Treatment is the same as for the earthy flavor, and also afterwards pouring in a quart or more of old brandy.
The bitterness here mentioned is only that met with in new wines, and its cause is entirely different from that found in old wines, which is described further on.
The Taste of the Stems, which often accompanies bitterness, is due to a prolonged immersion of the stems in the wine. It is supposed that this defect, which gives the wine a wild and common flavor, comes from an aromatic principle contained in the stems. It is prevented by stemming, and like natural bitterness, diminishes with time. The treatment is the same.
An unreasonably long vatting is one of the principal causes of bitterness and stem flavor.