When Necessary.—Wines do not always acquire the desirable state of brightness and limpidity by repose and racking, and it becomes necessary to clarify them. They may become cloudy through secondary fermentations, which cause the lees once deposited to rise and become again mixed with the liquid, or through changes of temperature, by transportation, by careless racking, etc., and by mixing different kinds together; or they may fail to clear naturally, because not possessed of sufficient tannin or albumen to precipitate the different matters held in suspension. Weak wines of poor years may contain ferments in excess of their sugar, which may be removed by clarification, and so fermentation be checked or retarded. Wines, however, which are well made and properly cared for, ought to become bright without recourse to clarification, and such will be found preferable to, and will possess more fruitness, unctuosity, and color, than those which have been clarified by several finings. And for these reasons—although it may be necessary to fine such wines as do not naturally clear themselves—care must be observed not to carry the process too far, and deprive them of the tannin necessary to their preservation, as well as of too much of their color, fruity flavor, and mellowness.
The Different Substances Employed for Clarifying act either chemically and mechanically, or simply mechanically. Among the latter are blotting paper, either in sheets or in pulp, fine sand, and powdered stone, which are placed in the cask, and which in falling, carry down with them the matters which are held in suspension. Wine is sometimes clarified by filtering it through woolen bags. Those substances which act both chemically and mechanically are albumen and gelatine, and similar substances.
Of Gelatinous Substances, two kinds are used, gelatine, so-called, and isinglass, or fish glue, and they act in two ways. They are not entirely dissolved in water; thin, transparent pellicles remain in suspension, which form a sort of network in the wine, and in settling they carry with them other insoluble matters. Thus, their action is mechanical. The portion which is fully dissolved is pure gelatine, and acts chemically. It combines with the tannin of the wine and forms an insoluble substance, tannate of gelatine, which is readily precipitated.
Gelatine, so-called, is prepared from the bones, skin, and tendons of animals, and is sold in tablets or sheets, and is sometimes chipped or broken into small fragments. It is one of the most powerful of finings, and causes a loss by precipitation of a considerable portion of the tannin and of the coloring matter of the wine. It should not, therefore, be used in clarifying red wines, except when it is desirable to deprive them of a portion of their roughness caused by an excess of tannin, or of a portion of their color; and it should always be employed with caution. It produces more sediment than the two substances next named, and leaves a bad taste in the wine, unless perfectly fresh matters have been used in its preparation. For the latter reason, wine clarified with it should be racked from the finings as soon as cleared. It may be profitably used to clarify common white wines; and if they are difficult to clarify, tannin should be added as described below.
Preparation.—Take about two tablets, or one ounce, for one hundred gallons, or double the quantity, if the greatest possible effect is desired. Dissolve it in a dish over the fire with a little water, constantly stirring, and do not allow the water to boil. If previously soaked a few hours in water, it will dissolve all the more easily. Use as directed below.
Isinglass, Fish Glue, or Ichthyocol (Ichthyocolla of the pharmacists), is prepared from the swimming bladder of the sturgeon, and usually comes from Russia. It acts in the same way as gelatine, mechanically, and also by combining with the tannin. This is preëminently the fining for white wine. One ounce or more maybe used for 100 gallons. It should be broken up by pounding it with a hammer on a block of wood, and should be chopped into small fragments, so that it may be easily dissolved. Put it in a vessel of crockery, and pour over it of the wine to be clarified sufficient to cover it. Add another glass or two of the wine in a few hours, when the first has been absorbed. After about twenty-four hours it forms a jelly. This should be thinned by adding more wine or warm water, and it should be thoroughly worked with the hand until completely dissolved, and then be strained through a piece of linen, using sufficient pressure to squeeze out the mucilage. It should be thoroughly whipped or beaten, and more wine is added if too thick. After being prepared, it may be kept for some time in bottles, by adding a little brandy. In clarifying sweet white wines, it is recommended that an ounce or two of cream of tartar be added, which must first be dissolved in warm water.
Albuminous Substances.—Among these are mentioned the blood of animals, dried or fresh, and it is a powerful clarifier. About two quarts to 100 gallons are used, beaten up with an equal quantity of wine. It is liable to deprive the wine of a portion of its color, and sometimes conveys a disagreeable flavor, particularly unless used when quite fresh. It should not be used to clarify old or fine wines, but may be employed for new and common ones. It is of use in clarifying white wines which have turned yellow, for it effectually removes this color. It should be used sparingly, if at all, for red wines, and the wine should be drawn from the finings as promptly as possible.
Milk is also used in the same way and in the same quantity as blood. It is liable to sour, and a small quantity is apt to remain in the wine. By its use sugar of milk is introduced, which is liable to undergo lactic and butyric fermentations, and the flavor of sour milk and rancid butter may be communicated to the wine. This may also be used to decolor white wine which has become yellow.
The White of Eggs is the best of the albuminous substances used for clarifying. It is coagulated by the alcohol and tannin, and forms a precipitate heavier than the liquid, and as it falls, carries with it the matters remaining in suspension. If the eggs are fresh, as they always must be, there is no danger of communicating any foreign flavor to the wine by their use; but it is not advisable to use the yolks, for they injure the wine by decoloring it, and the sulphur contained in them may communicate the odor of sulphuretted hydrogen. This is preëminently the fining for red wine. It is also used for the clarification of white wine, but Machard says that it is subject to be condensed in the form of splinters (esquilles), which obscure rather than clarify the liquid. The whites of ten or a dozen eggs are used for 100 gallons. They are beaten up in a small quantity of wine or water before using.
Clarifying Powders.—In addition to the substances mentioned, there are special preparations in the form of powders, sold for the purpose, which are highly recommended by some authors. They are supposed to consist mainly of dried blood; directions for using are given on the package.