Very little is known about the origin of these substances. Their presence might be due to secondary fermentations, which are pro duced by fission fungi, schizomycetes, but the yeast itself may also have a certain Influence, as certain yeast species are capable of produc ing fermentation products of a definite aroma and taste. For example: Saccharomyces ellipsoideus produces a peculiar fruit bouquet. It is well known that aging or yeast furnishes a product with more impurities than a sound and vigorous yeast. The raw material used in the distillery must also be considered. The corn, rye and potato fusel oil differ in com position, so that through experience one is enabled to detect the materials used, by the odor of the raw spirit. The fusel oil of the rye spirit contains, besides amylic alcohol, aromatic cenanthic ether; the molasses spirit contains the ethers of caproic acid, capric acid, caprilic acid, etc., which are very similar to the so-called oil of wine. Finally, the construction of the dis tillatory apparatus also influences the quality of the product. High pressure and too long a sojourn of the alcoholic vapors in the rectifi-, cator or dephlegmator are also said to be detrimental.
As it is necessary for some industries to use pure alcohol, these impurities are generally re moved by either of two processes : (1) Filtra tion of the raw spirit through charcoal; (2) re fining, by fractional distillation, or, in some cases, a combination of both.
In the manufacture of brandies, the former method is generally and successfully used, as a trace of impurity gives the brandy its charac teristic aroma and taste. Finely powdered char coal made from soft wood or bark serves as the filtering medium. It is well known that charcoal, by virtue of its absorbing capacity, acts as a decolorizer and deodorant, but in order to effect thorough absorption, the spirit must be diluted to about 40 per cent by volume (80 proof). In smaller plants the filter consists of a vat packed with charcoal. The larger dis tilleries and refineries use a battery of iron cylinders packed with granular or powdered charcoal. Steam is conducted into the battery until the charcoal is thoroughly saturated; then the spirits flow in, displacing the steam and fill ing the pores of the charcoal. The larger part of the impurities is absorbed in the lower cylinder, while the remaining impurities are removed dur ing the passage. through the remaining cylinders. If a filter is ineffective, it is cut out, the spirit is drawn off, steam is introduced, which forces the distillate into the condenser. This distillate
constitutes the so-called ((feints?) The feints is a dilute spirit, which is milky in appearance on account of the presence of fusel oil in emulsion. After standing, the fusel separates and can then be utilized, while the alcoholic liquid is worked up anew. The emptied filter ing cylinder is repacked with charcoal and used as the last filter. The used charcoal is either ignited in a special furnace, or else purified by means of superheated steam.
Refining of Spirits.— In order to produce an entirely fusel-free and highly concentrated alco hol, which is used for blending wine, cognac, etc., as well for scientific and certain techni cal purposes, the filtered alcohol must undergo a, fractional distillation. It is essential that the alcohol, whether filtered or not, be diluted to about 40 to 50 per cent by volume (80 to 100 proof ).
The rectificator for refining in general is the same as the distilling apparatus, but, inasmuch as the operation is a fractional one, it is an intermittent one. The columns are equipped with caps, bells or sieves.
Through distillation we receive: 1. The first runnings or fore-shot. This is the first distillate which contains those impurities of the alcohol which vaporize at a tem perature below the boiling point of the latter. Among these impurities acetic aldehyde is especially predominant.
2. Rectified fine spirit, which is divided into several distinct products, of which the first still contains some substances vaporizable at a low temperature and the intermediate products are pure alcohol, while the last portions already contain substances which volatilize at tempera tures above the. boiling point of alcohol. All of these products are separately collected at different intervals and furnish: (a) Wine spirit, commercially known as Cologne spirit. It contains 96 per cent of alco hol by volume (192 proof).
(b) Prime spirit, which is technically abso lute alcohol. For medicinal purposes it meets the requirements of the alcohol deodoratum of the United States Pharmacopoeia. It contains 94 to 95 per cent alcohol by volume (188 to 190 proof).
(c) Common spirit or high wine, commer cially called °rectified It is used for blending wine and cognac for medicinal and all other purposes when a pure, fusel-free, less con centrated alcohol than the foregoing is neces sary. It contains about 90 per cent by volume (180 proof).
(d) Alcohol of about 88 per cent by volume (176 proof), which can be used for blending brandies as well as for preparing dilute alcohol (97 to 100 proof).