The general principles of the first three of the preceding operations are noticed in the articles Brewing, Fermentation, &c. It will there be seen that the amylaceous or starchy matter of the grain is first ‘saccharified,’ and afterwards converted into alcohol, and that certain precautions are necessary to render the process successful and economical. In many of the distilleries of Great Britain molasses and analogous saccharine substances are employed, in which case the vegetable principle (sugar) essential to the formation of alcohol is already present, and merely requires simple solution in water of a proper temperature, to be ready to be subjected to immediate fermentation. In general, however, the sources of spirit in England are the various kinds of grain; barley, rye, maize, and rice are those commonly employed. These are ground and mixed with bruised malt, in various proportions, and are mashed in a similar manner to malted grain. The fermentation is carried on until the density of the liquor ceases to lessen or ‘attenuate,’ which is determined by an instrument called a saccharometer. When this point is arrived at, the ‘wash’ is submitted to distillation, to prevent the access of the acetous fermentation, which would lessen its alcoholic value.
During the process of distilling off the spirit of the fermented ‘wash’ or ‘wort’ a hydrometer is employed to ascertain the ‘strength’ of the liquor that passes over. As soon as this has fallen to a certain point, the operation is stopped, and the ‘spent wash’ removed. The spirits obtained by the first distillation are generally called ‘low wines,’ and have a specific gravity of about ·975. By rectification or ‘doubling,’ a crude milky spirit, abounding in oil, at first comes over, followed by clear spirit, which is received in a separate vessel. The process is continued until the alcoholic content of the distilled liquor has considerably diminished, when the remaining weak spirit that distils over, called ‘faints,’ is caught separately, and mixed with the low wines preparatory to another distillation. The strongest spirit passes over first, and the condensed liquor gradually becomes weaker, until it ceases to contain alcohol. By receiving in separate vessels any given portion of the product, spirit of any required strength, within certain limits, may be obtained. The same object is more conveniently effected by surrounding the top
of the capital of the still with a water bath, of a temperature corresponding to that of alcoholic vapour of the strength it is desired to obtain. Thus, if we keep the temperature of the water at about 198° Fahr., we shall obtain proof spirit; if at 192°, a spirit 20 o. p.; and so on for other strengths.
It is found from experience, and is readily accounted for by theory, that the lower the temperature at which the distillation is conducted, the stronger will be the product, and the less quantity of oil or other volatile matter will come over along with it. To promote this, it has been proposed to carry on the process in vacuo, but on the large scale this has never been adopted. The distillation of the wash is usually performed in a separate set of stills to those employed for the rectification of the low wines. For very strong and tasteless spirit, a third and even a fourth rectification is employed, conjointly with other methods, to abstract the water and to remove any foreign matter that vitiates its odour or flavour. A portion of soap is generally put into the still with the wash, to prevent excessive frothing.
We have said that the processes of mashing, &c., in the distillery are similar to those adopted in brewing beer. We may add that, as richness in alcohol, and not flavour, is the object aimed at in the distiller’s wash, not only is a large quantity of unmalted grain employed, but the process of boiling the wort with hops is omitted altogether. The wort is commonly ‘set’ at 70° Fahr., and the fermentation and attenuation of the liquor pushed as far as possible by large and repeated doses of the best ‘top-yeast’ of the porter brewers.
It often happens that raw spirit prepared from damaged grain is contaminated with a highly acrid and volatile fatty substance, which is powerfully intoxicating and irritating to the eyes and nostrils, and possesses an odour very similar to that of an alcoholic solution of cyanogen. This may be got rid of by dilution with water and skilful rectification, when most of it passes over with the first and last ‘runnings,’ the intermediate portion being less loaded with it. Another plan is to filter the spirit successively through 6 or 7 separate vessels containing pine or willow charcoal before rectifying it. In some distilleries the contaminated spirit is well agitated with a considerable quantity of olive oil, and after repose decanted, diluted with water, and rectified as before. The ordinary corn oil or fusel oil of raw spirit is generally, for the most part, intercepted by a self-regulating bath arranged between the still-head and the refrigeratory.
The quantity of spirit obtained from various substances, and even from pure sugar, depends upon the skill with which the several operations are conducted. By theory, pure sugar should yield 51% of alcohol; but in practice 11·925 galls. of proof spirit is the largest quantity which has yet been obtained from 112 lbs. of sugar. By the revenue authorities this weight of sugar is estimated to afford 111⁄2 galls. of proof spirit. The average product is, perhaps, about 1 gall. of spirit of this strength for every 10 lbs. of sugar. According to Harmstädt, 100 lbs. of starch yield 35 lbs. of alcohol, or 7·8 galls. of proof spirit; and 100 lbs. of the following grains produce the accompanying quantities by weight of spirit of sp. gr. ·9427, or containing 45% of pure alcohol:—wheat, 40 to 45%; rye, 36 to 42%; barley, 40%; oats, 36%; buckwheat, 40%; maize, 40%; the mean being 3·47 galls. of proof spirit. It is found that a bushel of good malt yields 2 galls. of proof spirit, and that the largest quantity of proof spirit obtained from raw grain, mashed with 1⁄5 or 1⁄6 of malt, does not exceed 22 galls. per quarter.
The distiller is allowed to produce worts from any substance, and at any specific gravity, provided such gravity can be correctly ascertained by the saccharometer approved of by the Board of Inland Revenue. He is not, however, allowed to mash and distil at the same time. See Alcohol, Brandy, Fermentation, Fusel Oil, Gin, Still, &c.
DISTOMATA. A genus of fluke-like parasites infesting men and the higher vertebrate animals. The egg is about the 1⁄280th of an inch long and 1⁄270th inch wide.
