liquid is turned first to alcohol, and the alcohol then changes to acetic acid, which is the acid in vinegar.
In Great Britain, vinegar, until recently, has been manufactured almost entirely from malt—a wort, or sugary solution, weaker than is employed for beer, being first made. Of late years, glucose, cane-sugar, and molasses, have been largely used. British "proof-vinegar" contains 4.6 per cent of anhydrous acid, A notion formerly prevailed that sulphuric acid acted as a preservative to vinegar, and one tenth of one per cent was allowed to be added. Makers continued the practice after they knew that it had no such effect, as it increased the apparent strength of their vinegar at a slight cost. This addition is now an illegal adulteration.
In France, and elsewhere in Europe, the manufacturer starts with an alcoholic liquid, already partly acetified—light wines that have turned sour being generally employed. The French name, vinaigre, from which the English word vinegar is derived, means sour wine. Two sorts are produced—white-wine and red-wine vinegar—the former being generally preferred. These are fine-flavored and somewhat stronger than the malt-vinegar of Great Britain. Six and one half to seven per cent of acid have been found in French vinegars. Sour ale and beer do not yield good vinegar.
In the United States, cider vinegar has long held the preference, and, if the cider has been made from sound, sweet apples, the vinegar has a very agreeable flavor and color. The old-fashioned way which is followed by farmers in making vinegar is to set out-of-doors in the spring a barrel of cider which has become too "hard" and sour to drink, from the sugar partly turning to alcohol and acetic acid. The bung is taken out of the barrel, and the bung-hole is loosely stopped by sticking the neck of a large bottle into it. Such exposure to the air at a warm temperature effects the conversion of the cider to vinegar in three or four months. The change goes on very slowly, because the air can act only on the surface of the liquid, and fresh portions of alcohol are brought to the surface only as the newly formed acid sinks and mingles with the liquid below. The best cider-vinegar is made from new cider, and it is well to cause several fermentations to take place by adding a fresh quantity of cider every two weeks.
Vinegar is chemically a dilute solution of acetic acid, containing minute quantities of fragrant ethers, which give it its odor, and some brownish substance, to which is due its color. Other matters, derived from the liquid from which the vinegar is made, are sometimes accidentally present, as sugar, gum, starch, cream of tartar, and other salts, etc. It usually consists of between ninety-three and ninety-seven per cent of water, the rest being acid, except a fraction of a per cent of solids. The transformation of the sugar in fruit juices or sirups to acetic acid takes place according to the following chemical reactions:
