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.

Gum Arabic, about 10 ounces to 100 gallons, is also used, but it is not readily precipitated, and is apt to remain in dissolution in the wine.

Salt is often added to the different finings, by first dissolving a small handful in water. It renders them heavier, and as it is insoluble in alcohol, it becomes precipitated, and thus acts in two ways. Many authors recommend its use, but Boireau says it should only be employed in clarifying common or very turbid wines.

Alcohol is added with great advantage if the wines are so weak in spirit that the finings do not act.

Tannin, however, more frequently requires to be added, for upon it and the alcohol depends the action of the substances employed. If the wine is not lacking in alcohol, and the finings do not act, sufficient tannin must be added to produce the desired effect. If the ordinary tannic acid of commerce is employed, one-half to one ounce for 100 gallons may be used. Dissolve ½ lb. in a quart of the strongest alcohol, 95°, by thoroughly shaking in a bottle of double the size. After standing twenty-four hours it is filtered, and one gill of the solution contains one ounce of tannic acid. This preparation of tannin, which is prepared from nutgalls, is used for tannifying sparkling wines, because it does not adhere to the inside of the bottle. It is preferable, however, in general to employ the tannin derived from the vine itself. For this purpose a strong decoction is made by steeping grape seeds, which have not undergone fermentation, in water. They should be coarsely broken, or bruised, and boiled for several hours. By adding from one-fourth to one-fifth of its volume of strong alcohol of 85 per cent., it can be kept for future use. The liquor may be filtered before adding the alcohol. Instead of the seeds, sometimes a handful of stems are steeped, and the liquid is used. Tannified wine may be prepared by soaking 50 or 60 lbs. of the bruised seeds in 100 gallons of white wine, for one or two months. It is cared for as white wine. If only one cask is to be treated, say 100 gallons, one-half pound of grape seed may be reduced to powder and put in.

It is difficult to lay down a definite rule as to the amount of either preparation to use, for the reason that the amount of tannin contained in the wine itself varies. Three or four gallons of the tannified wine are recommended for 100 gallons, and a much smaller quantity of the first mentioned decoction would be equivalent in its effects, on account of its additional strength. If, however, it is found that sufficient has not been used, the wine must be clarified anew, and tannin added again. By experimenting on a small quantity of the wine, the proper quantity may be ascertained.

Method of Operation.—After preparing the finings as described under the head of each of the substances already mentioned, two or three gallons of wine are drawn from the bung by the aid of a siphon, pump, or other suitable implement, the finings are poured in, and the wine is stirred until thoroughly mixed with them. This may be done with a stick split at the end into three or four prongs (fig. 24), or by a sort of brush consisting of several small bundles of bristles inserted in a stick and at right angles to each other (fig. 25), or with a sort of bent paddle, pierced with holes, called a whip (fig. 26). The wine drawn out should then be replaced in the cask, which should be completely filled, and left to rest till the wine is bright. In filling a cask which has recently been agitated, or into which finings have been put, a good deal of froth is frequently found which will run out at the bung before the cask is full, and will prevent the operator from filling it. A few smart blows on the bung stave with a bung starter will break the bubbles and remove the foam. The time required to clarify a cask of wine depends somewhat upon the quality of the wine itself, and also upon the kind of finings used. The usual time is from two weeks to a month. In no case, however, should it be allowed to remain on the finings after it has cleared and has ceased to deposit, for the sediment may work up again and cloud the wine, and if left too long in contact with the deposit, the wine may acquire a disagreeable flavor.

If, after leaving the wine a suitable time, it still remains turbid and continues to deposit, it should be racked into a clean cask and fined again, adding tannin, if necessary.