This section is from the book "Alcohol, Its Production, Properties, Chemistry, And Industrial Applications", by Charles Simmonds. Also available from Amazon: Alcohol: Its Production, Properties, Chemistry, And Industrial Applications.
In this country very little alcohol is used for vinegar making. On the Continent, however, a large quantity is employed for the purpose, more than three millions of gallons being used yearly in Germany alone. The product is largely employed for ordinary domestic and preserving requirements; the quantity used industrially is mainly devoted to the making of white lead and pharmaceutical lead acetate. To some extent also it is used as a source of pure acetic acid, but it here competes with the acid derived from distillation of wood, and success or failure depends upon the price of the alcohol.
The process of manufacture is that of " acetification," or oxidation of the alcohol by means of Bacterium aceti and allied organisms. The most suitable of these are used as pure cultures. Pure aqueous alcohol alone, however, does not suffice as a medium in which acetic fermentation can take place, since nitrogenous substances and salts are necessary for the growth of the organisms. Cane sugar or glucose syrup (capillaire) is usually added, in the proportion of 1 to 3 kilos. per 100 litres of pure alcohol present in the "goods ' or mash, to supply the carbon requirements of the acetic bacteria; while the nitrogenous needs are met with the requisite salts. Most of the modern spirit-vinegar factories use inorganic salts, chiefly acid phosphate of ammonium, sodium, and potassium, and also ammonium and magnesium sulphates. These salts are arranged so as to correct any deficiency of mineral matter in the water supply. About 50 to 150 grams are used per 100 litres of pure alcohol. Beer and malt extracts are also employed as nutrients instead of the salts and syrups.
1 Tischtschenko, Chem. Zentr., 190G, 2, 1309, 1552.
The acetification vessels are generally of cylindrical form, from 1 to 2 metres in diameter, and 2 to 3 metres high. They usually contain beech wood shavings, resting on a perforated false bottom, and covered with a similar perforated disc. In the sides are holes for access of air, a supply of which is necessary for the oxidation.
The alcohol is diluted to a strength of 6 to 10 per cent., mixed with the requisite nutrient materials, and delivered on the top of the shavings by means of a rotating sparger. Where the latter is not provided, the liquid is simply poured upon the upper perforated plate, and led into the interior by means of short pieces of twine passing through the holes. When starting with a newly-packed vessel, the pure culture of the bacterium is mixed with the first charge of alcohol; subsequently some of the acetified product is used for mixing with the charges.
The diluted alcohol trickles downwards through the shavings, on which the ferment secures a lodgment, and is gradually oxidised as it passes down. The temperature of the acetifying room is kept at 20-25°; and that of the vessel, in which heat is developed by the action of the ferment, is maintained at 25-35° by controlling the admission of air and of the alcoholic charge. The resulting vinegar collects in the bottom of the vessel and passes out through a swan-neck tube. It should still contain a few tenths per cent. of alcohol, since if the latter is completely converted, the acetic bacteria are liable further to attack the acid itself and diminish the yield.
Ordinarily, the product obtained by this process contains from 4 to 6 per cent. of acetic acid; a much stronger acid is liable to weaken or destroy the acetic bacteria. "Double "or 'triple ' strength products can, however, be produced by mixing the ordinary vinegar with fresh alcohol and treatment in other vessels containing suitable organisms. Up to 12 per cent. of acid can thus be obtained in the liquid.
Spirit vinegar naturally contains more or less extractive matter, arising from the sugar and nitrogenous substances used as nutriments. The yield is about 80 per cent. of the theoretical; much loss occurs through escape of alcoholic and acid vapours, though in some of the factories apparatus is installed to recover these.