Vinegar is made by the oxidation of alcohol, either directly or through the medium of a ferment, or by the distillation of wood; the latter is known as pyroligneous acid. Any substance capable of fermentation or any containing alcohol is suitable for making vinegar. It is made in the slow way from wine, cider, beer, sugar, or honey and water, whiskey and water juice of plants and vegetables; in the quick way from a spirit prepared for the purpose.
_Slow Method of Making Vinegar._
This is the process usually adopted in the small scale. The "wash," as any weak alcoholic liquor is called, should be weak, from 5 to 10 per cent. of alcohol is best; too strong a liquor will ferment very slowly; the strength is best judged by the taste. The temperature should be from 74 to 86 Fahr. Sour beer, wine, or cider are better than good liquors. Th e addition of sugar, honey, or other sweet matter with a view of strengthening the vinegar is not to be recommended, as it renders the vinegar liable to spoil. Ordinary fermented liquors are quite alcoholic enough.
The best ferment is vinegar, an old cask in which good vinegar has been kept is the best to ferment in. Other ferments are used, as bread soaked in brewer's yeast, sour dough, dough of wheat and rye flour soaked in cream of tartar and vinegar, all these are used in small quantity, a few ounces to a barrel of wash. Vinegar made with them is more apt to spoil. The more ferment present the quicker the process.
The wash is put into the cask, which is best painted black in order to absorb the sun's rays when the weather is cool; the bung is left out, the bung-hole covered with a piece of slate, and in about 4 weeks the acetification is complete. The lower the temperature the slower the change.
_To Purify Vinegar._
After all the mothers are deposited, draw it off into a vessel filled with beech-shavings, and let it stand in a cool place until clear. Vinegar is apt to be infested with flies (Musca cellaris), and eels (Vibrio aceti). These may be killed by passing it through a coiled tube dipped in boiling water.
Vinegar (especially when weak) if exposed to the air becomes thick or mothery, and deposits a mucilaginous substance; the vinegar becomes weak and mouldy as this change goes on.
When vinegar is barrelled, a pint of spirits should be added to each barrel to secure its keeping. It should be kept in a cool place.
_Varieties of Vinegar._
Wine Vinegar, made from wine, contains citric and tartaric acid, and a small portion of acetic ether, which communicates an agreeable flavor. It is imitated by adding acetic ether and coloring matter to vinegar made from whiskey.
Cider Vinegar (which includes all fruit vinegars) contains malic acid.
Malt, or Corn Vinegar, made from weak worts, contains phosphates of lime and magnesia, gum, and extractive matter.
Wood Vinegar or pyroligneous acid, when crude, contains tar and wood spirit.
_Adulterations of Vinegar._
Sulphuric, nitric and muriatic acids, are used to give a false strength; burned sugar and acetic ether to give color and flavor. The latter cannot be considered as injurious. One one-thousandth of mineral acid is allowable, and tends to preserve the vinegar. This would be about four measured ounces to the barrel, or two to the ordinary halfbarrel.
Sulphuric acid is detected by boiling with chloride of calcium; baryta is not admissible as a test for sulphuric acid in vinegar.
Muriatic acid gives a white, curdy precipitate, with a solution of nitrate of silver. This precipitate is soluble in ammonia, and blackens on exposure to light.
Nitric acid is detected by adding muriatic acid. If the solution will dissolve gold leaf, nitric acid is present.
_To Strengthen Vinegar._
Freeze it and remove the floe which forms on the surface. The water of the vinegar alone freezes leaving the acetic acid in solution in the remaining water.
_To Determine the Strength of Vinegar._
The hydrometer (see SPECIFIC GRAVITY) is not to be much relied on in testing the strength of vinegar. The simplest test is to take a fragment of fine marble, weigh it and suspend it by a thread in a known measure of vinegar until all action ceases and the liquid has no longer a sour taste. Take out the marble, wash and dry it, and note the loss of weight it has sustained. Five-sixths of this is real (hydrated) acetic acid. An ounce of good vinegar should saturate from 30 to 32 grs. of pure and dry carbonate of soda; such vinegar contains about 5 per cent. of anhydrous (absolute) acetic acid. Vinegar above 30 per cent. of real acid will dissolve the essential oils and camphor.
_Simple continuous Vinegar Process._
The following household vinegar method is to be recommended as simple, expeditious, and furnishing a constant supply of vinegar with scarcely any trouble, and at trifling cost: Two barrels are procured, one for making, the other for storing the vinegar. Those from which good vinegar has just been drawn are preferable. The storage barrel is kept always in the cellar, the generating one in the cellar or house, according to the season. In this latter barrel a small hole is bored, for the circulation of air, at the top of one of its heads. The barrels lie on their side, and contain each a wooden faucet. Of course their capacity is regulated by the yearly demand of vinegar.
We will suppose that the generator, filled to the level of the ventilating hole, contains 10 galls.; the manufacture will then be carried on in the following manner: Seven galls. of good vinegar are poured in it, and 3 galls. of a warm alcoholic mixture made in the following manner and added: If common whiskey (50 per cent.) be employed have a small measure of 3 pts. and a large one (a bucket) of 3 galls. If 86 per cent. spirits are used let the small measure be for 2 pts. Put a small measureful of the spirits in the large measure; fill quickly to the mark with boiling water, and pour by a funnel into the generator. Every 2 or 3 weeks 3 galls. of vinegar are withdrawn from the generator, added to the storage barrel, and 3 galls. of alcoholic mixture are placed in the generating barrel as before.
Another method of working the casks consists in half filling the generator with vinegar and adding every week so much of the alcoholic mixture that it fills the barrel in from 8 to 16 weeks, according to the season. Half the vinegar is then added to the storage cask, and the process recommenced in the generator. The warfer the season the more rapid may be the manufacture.--Wetherill on the Manufacture of Vinegar.
Vinegar without a Ferment (Dobereiner's Process), The ferment used in the manufacture of vinegar is not necessary. Alcohol may be oxidized directly by the agency of finely divided platinum (platinum black); 10 per cent. alcohol placed in a close vessel with platinum black is rapidly converted into acetic acid. dr. Ure estimates that with a box of 12 ft. cube and 6 to 8 oz. of strong platinum, 1 lb. of alcohol daily can be converted into acetic acid, and with from 20 to 30 lbs. we may obtain 300 lbs. of vinegar from the proportionate quantity of spirits. The same platinum black will last for an indefinite time, requiring only to be heated to redness from time to time, to restore it. This method is undoubtedly the most elegant one known of vinegar manufacture, and has been tried on a large scale in Germany. The objection to it is, however, the high cost of the platinum in which a large amount of capital must necessarily be kept looked up.
_The continuous Quick Vinegar Process._
This is the method almost universally adopted for manufacturing vinegar on the large scale. Common new whiskey makes excellent vinegar; the fusel oil becoming oxidized during the process, is converted in harmless, agreeable ether. It is diluted so as to form a wash of about 6 per cent. alcohol. Two tubs, or upright casks, are prepared as follows: A false top and bottom are inserted. In the false top are bored numerous holes one tenth of an inch in diameter and 1 1/2 in. apart, the top is fixed water-tight about 6 to 8 in. from the top of the barrel. At from 8 to 14 in. above the bottom of the tube are bored 1/2 in. air-holes, inclining downwards so that the liquid may not flow out. About 2 in. above the air-holes is placed the false bottom pierced with 1/2 in. or inch holes. The space between the false top and bottom is filled with closely-curled beech-shavings, or charcoal in lumps of the size of a walnut, sifted, washed and dried. The holes in the false top are filled with lamp-wick, and the space below the false bottom provided with a stopcook, or gooseneck. There is also an inclined hole 6 in. below the false top for the insertion of a thermometer and hour-glass, or wood tubes are inserted into the false top, reaching nearly to the cover of the tub; these act as chimneys. The beech shavings are boiled in vinegar and pressed into their place until within 6 in. of the false top or sieve. Before starting the process the room and tubs are to be kept a day at a temperature of 75 to 80 Fahr.
The shavings at the thermometer hole, and at the lower ventilating holes, are then loosened by means of a stick thrust therein. A wash is now prepared which contains 1-5 vinegar and 4-5 of a 3 per cent. solution of alcohol; this heated to from 75 to 80, is gradually poured through the hole in the cover of the generator, at the rate of 1 barrel in 24 hours. At the expiration of this time, warm the resulting vinegar if necessary, and having alcohol enough to make the whole quantity taken thus far of 5 per cent. alcoholic strength, pour this through the generators as before. Repeat this operation on the third, and even on the fourth day if necessary. Investigate the temperature of the air escaping from the generator, and when it exceeds that of the wash which is running, it is a sign that the acetification has commenced. When it rises to a point between 98 and 104, the generators are in a proper condition to commence the regular business of the manufacture; the fermentation has been properly established. We then daily pour through generator No. 1 a wah consisting of a certain quantity of spirits, vinegar, and water heated to a temperature between 75 and 80 Fahr.; and through No. 2 the wash has passed through No. 1, to which has been added more spirits. We draw manufactured vinegar daily from generator No. 2. The vinegar resulting from setting the generators in action, though not prejudicial to health, is of inferior quality and bad flavor, from extractive matter from the shavings and tubs and from the iron cauldron. It may be added in very smell quantity to the subsequent vinegar, if it be not thrown away. - Wetherill on the manufacture of Vinegar.
_To make Quass._
Mix rye flour and warm water together, and leave it till it has turned sour. This vinegar is much drunk in Russia; it looks thick and unpleasant at first, but becomes agreeable by use.
This is obtained from vinegar by distillation, rejecting the fourth or eighth part that comes over first, and avoid its aquiring a burnt flavor.
Distilled vinegar is weaker than the common but is used sometimes in pickles, where its want of color is an advantage.
_To Deprive Vinegar and other vegetable Liquids of their Color._
To take away the color of vinegar, a litre of red wine vinegar, cold, is mixed with 45 grammes of bone-charcoal, in a glass vessel. Shake this mixture from time to time, and in 2 or 3 days the color completely disappears. When the process is to be performed in the large way, throw the charcoal into a cask of vinegar, which must be stirred from time to time. The highest colored red wines treated in the same manner become perfectly limpid. Ivory-black possesses the same property as bone-black.
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