Casks are sulphured for the purpose of destroying the activity of the ferments contained in the lees which may remain in them, and thereby to prevent their moulding or souring, and must and wine are sulphured to prevent or to check fermentation, and white wine also to keep it from turning yellow.

Sulphurous Oxide, or Sulphur Dioxide, is produced by burning sulphur. It is a colorless gas, of a suffocating odor, and is composed of equal weights of sulphur and oxygen, or, one part of the former and two of the latter, SO₂, and with water becomes sulphurous acid. It arrests fermentation in two ways: first, it absorbs oxygen with avidity, and thereby removes what may be in the must or wine, or in the cask, thus taking away one of the conditions necessary to the life and activity of the ferment. (See Fermentation.) In the second place, by the absorption of oxygen, sulphuric acid is formed from the sulphurous acid, in a highly concentrated state, which is destructive of the life of the ferment.

The Sulphurer, or Sulphur Burner, the instrument used for the purpose indicated, consists of a wire with a hook at one end, and the other attached to the centre of a long, conical bung (fig. 13). It is convenient to have the upper end pass entirely through the bung, allowing the latter to move up and down on the wire, so that the hook can be raised or lowered, according to the position to be occupied in the cask. This is used by attaching the sulphur match to the hook and lowering it into the cask, after lighting it. The objection to this form of instrument is, that the coal or cinder left on the hook, after burning the match, may fall into the cask and give the wine an unpleasant flavor. To avoid this, Mr. Maumené invented a sulphurer, provided with a deep perforated porcelain cup, into which the match is placed and in which it burns, and which retains the carbonized linen (fig. 14). A piece of wire cloth bent into a cup of a similar form and attached to the lower end of the wire answers the purpose very well.

Sulphur Matches or Bands may be purchased, or they may be easily manufactured. To make them, melt roll brimstone (stick brimstone), or what is better, flowers of sulphur, over a slow fire (sulphur melts at 115° C. or 239° F.); tear linen or cotton cloth into strips an inch and a half wide and 10 or 12 inches long, and dip them into the melted sulphur, and lay them aside to cool. Then dip again, and repeat the process, dipping and cooling, till the coating of sulphur is of the required thickness, and they should be thickly coated, or it may be necessary to burn too much linen to get sufficient gas. If the sulphur is overheated, the match will be dark-colored.

Sweet scented powders are often added to the sulphur, whose essential oils are disengaged when the sulphur is burned, and the cask is perfumed by their vapors. The substances usually employed are ginger, cinnamon, the flowers of the stock gilly, iris, lavender, thyme, violet, etc., and the matches prepared with the addition of them is generally preferred.

Mr. Maumené says that the smallest amount of this volatile oil gives a perfume to the wine, which is generally advantageous, but Boireau is of opinion, however, that these substances check the combustion of the sulphur, and in a measure neutralize its action, and he prefers the sulphur pure.

To Sulphur a Cask, take a piece of the sulphur match and light it and lower it into the middle of the cask by means of the sulphur burner, and lightly put in the bung of the instrument. By applying the ear to the staves, it can be ascertained if the match is burning. If the air is foul in the cask, and the match will not burn, the noxious gas must be expelled as described under the head of Casks. When the fire is extinguished the burner is withdrawn, care being taken, if the hook is used, not to drop any of the carbonized linen into the cask. If that should happen, the cask must be washed again. As the burning sulphur fills the cask with gas, which exerts considerable pressure, care should be taken that the bung is not blown out into the face of the operator.

Sometimes a strip of the sulphured cloth is lighted at one end and lowered into the cask, the other end being secured by putting in the bung. This is objectionable, because it leaves the debris of the match sticking to the bung and the stave, which may give a disagreeable flavor to the wine. As already mentioned under the head of Casks, never burn a match in a cask containing alcohol.

To Sulphur Wine, if the cask is only partly full, operate the same as in sulphuring an empty cask, only care must be taken not to lower the match into the wine. Here the sulphur burner with a movable bung comes in play. If the cask is full, the gas may be drawn in by burning a match close to a hole bored in the head of the cask somewhat higher than the faucet, drawing from the latter at the same time. It is evident that while the wine runs from the lower hole, the gas will be drawn in at the vent. Where it is necessary to leave a cask with a vacancy in it for some time, flowers and souring may be prevented by burning in it a piece of sulphur match and bunging it up, and the process should be repeated every two weeks, and besides as often as the bung is removed for any purpose. It is better always to keep the cask full, for in time the sulphurous gas will communicate a disagreeable taste to the wine, which it takes a long time to remove.

Sulphuring should be Avoided in Certain Cases.—Ropy wines should not be sulphured, for the presence of oxygen is necessary in order to help their fermentation; nor should those wines be sulphured which it is desirable to keep in a state of effervescence. Sulphur should be very sparingly used in connection with red wines, as it causes them to lose a portion of their color by rendering insoluble the coloring matter, and precipitating it; and for the same reason it is used for bleaching white wines, and it prevents the latter from turning yellow. Liqueur wines which are slow of fermentation should not be sulphured, for they need all the natural aids to fermentation.

Fermentation is Arrested, sometimes, in the manufacture of white wines, by drawing them off into well sulphured casks, using two or three squares of the match, if the fermentation is not very tumultuous; but if it is very active, it may be treated as mentioned below for musts. And in most cases the proper practice is, where wine needs sulphuring, to draw it off into the sulphured cask, and in this way the oxygen contained in the wine is more thoroughly exposed to the action of the gas.

Unfermented Must.—By sulphuring the must, fermentation is prevented, and thereby is produced what the French call mute wine; and it is the must of white grapes as it comes from the press that is more generally subjected to the process. It is first allowed to settle as described in the chapter on white wine, but it must be drawn from the vat as soon as signs of fermentation appear, and bubbles of carbonic acid rise to the surface. And to have the must clear, it must be closely watched, for as soon as fermentation sets in, it becomes turbid. The must should be freed from all fragments of stems, skins, seeds, etc., and should therefore be strained as it runs from the press.

It is Prepared in Two Different Ways.—First, the cask must be scalded, rinsed, and drained in the usual way, and then as much sulphur must be burned in it as can be consumed, or until the match goes out for want of oxygen. Then the cask must be rapidly made half full of the must, and closely bunged. It should then be rolled and thoroughly shaken until the gas has been well absorbed by the juice. The must is then drawn off without allowing it to come in contact with the air (See Racking), and into another cask which has been sulphured in the same manner, and is treated as before. While the second cask is being agitated, sulphur is again burned in the one just emptied, until it goes out, and then the must is transferred back in the same manner, and is again shaken. It is subjected to this operation four times, and the cask is finally filled with must treated in the same way, and tightly bunged. The more successful will the operation be, the more the liquid is kept from contact with the air, and therefore this method is preferable to the next. The second method is as follows: burn in an empty cask matches representing a couple of ounces of sulphur; pour in about five gallons of must, bung it up and thoroughly shake; take out the bung and put in another lighted match; if it will not burn for want of oxygen, the air must be renewed by blowing in the cask with a bellows. Then burn the match in the cask, and afterwards pour in five gallons more of must, bung and shake as before. Continue the process till the cask lacks about five gallons of being full. Then five gallons must be sulphured in another cask, and the cask filled up with this and tightly bunged. Of course, the sulphur burner must be shortened as the cask fills up.

Must treated in this manner may be kept for a long time if well clarified, and the cask is well sulphured at each racking, or a portion sulphured when it commences to ferment.

If it is only necessary to keep the must a short time, a portion only, say one-third, need be sulphured. In that case there will be less odor of sulphur, and it will soon pass away.

Clarification and Care of Unfermented Must.—It should be kept in good, strong casks, well hooped and well bunged, in closed cellars of a constant temperature. The casks should be filled every few days with sulphured must; and they should be frequently racked to free them from ferments. They should not be exposed to the air when racking, and should be racked into well sulphured casks. Boireau says that the must may be completely clarified before sulphuring, by introducing about one ounce of tannin per 100 gallons of must, and pouring into the casks before completely filling about a quart of water in which has been dissolved about four tablets of gelatine, and which has become cold.

A Sulphur Flavor is sometimes communicated to must treated as above, and is also sometimes acquired by wines which are put into casks which have been sulphured for some time, without first washing them, and also by allowing the debris of the sulphur match to fall into the cask; this flavor is apt to pass away with time if not very pronounced, or in that case may be removed by racking into a clean cask. But if the wine has a very decided sulphur flavor, it must be disinfected by wood charcoal. Several large pieces[3] of coal well cleaned and well dried are introduced into the cask and soaked in the wine, from which they can be withdrawn by strings attached before putting them in the cask. Forty-eight hours are generally sufficient to remove the flavor; but if necessary, the process may be repeated, by changing the charcoal. In operating on white wines, a large amount of charcoal may be used without inconvenience, but in the case of red wine, there seems to be some danger of depriving it of a portion of its color. Mr. Maumené says, however, that the charcoal is liable to deprive the wine of the carbonic acid dissolved in it, it being an absorbent of that gas, and thereby rendering the wine more subject to the action of oxygen.

Other Substances have been recommended to Prevent Fermentation in a Must, but notwithstanding the disagreeable flavor which is communicated by an excessive use of sulphur, no other agent has been found which is as satisfactory, on the whole.

By Burning Alcohol in the Cask, the oxygen may be removed, but the ferments are not destroyed. Care must be taken to avoid an explosion. Therefore, the spirit must not be poured into the cask and lighted, but must be placed in a small vessel and lowered in through the bung, as in the case of sulphuring.

The Concentrated Aqueous Solution of Sulphurous Acid has been recommended, but Maumené says that not only is its preservation very difficult, but its management is more difficult than the sulphur match, and the chances of its being mixed with dangerous substances are considerable; and therefore no one should think of using it.

The Bisulphite of Lime has been used to prevent fermentation in wine and cider, but it does not always give satisfactory results, and the salt is difficult to keep, and the use for wine, at least, has generally been abandoned. In the experiments of Proust, given by Maumené, the smallest quantity used was 15 grammes to 100 kilogrammes of must, or about one-half ounce to 23 gallons.

Salicylic Acid has been much recommended within the past few years, but like everything else, it affects the flavor, if sufficient is used to prevent fermentation. The quantity necessary depends upon the amount of alcohol, ferments, etc., contained in the wine. Prof. Neubauer, quoted by H. Endemann in American Chemist, says that wine which is yet fermenting should not receive any salicylic acid, since too large quantities of the substance are required for effective use, but that it may be used in wine when made to prevent after-fermentation; that it will prevent disease, but will not cure wine when diseased. Though infallible rules as to quantity cannot be given, experiments should be made with from .02 to .06 gramme per litre, or say from 1.165 to 3.5 grains per gallon. A solution of 2 grammes (30.864 grains) of salicylic acid to 100 c.c. (3.38 fluid ounces) of alcohol of 80° is employed; 1 c.c. = 0.02 grammes; 3 c.c. = 0.06 grammes; 61.44 minims or a little more than one fluidram = 1.165 grains, and 3.7 fluidrams = 3.5 grains. Salicylic acid being but sparingly soluble in water, it is preferable to dissolve in strong alcohol, and these are convenient proportions.

It is said that 100 grammes (3½ Ap. ounces) will stop the fermentation of 1000 litres (about 264 gals.) of must, when nearly completed; 800 grammes are necessary when in active fermentation; and 400 will preserve the wine when made.

But now the intelligence comes that salicylic acid has an injurious effect upon the teeth and bones, it having an affinity for calcareous salts (Boston Journal of Chemistry, Vol. XI, 143), and the French Minister of Agriculture and Commerce, on the report of the Committee of Public Hygiene, recommends that the sale of articles of food adulterated with it be prohibited as injurious to the public health. (Ib. Vol. XV., 45.)