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Upon examining the wash after the termination ofthe fermenting action, it was found that 4'34 parts ofthe sugar had been decomposed, and that 1 partremained intact; thus showing that when worts areeven purposely diluted, nearly a fifth part of the sac-charine matter will escape decomposition; and whereworts are much stronger, or more concentrated, ofcourse the loss will be much greater. On the largescale, the attenuation cannot often bo carried below1'0012. Some rare instances may occur, in whichthe specific gravity maybe reduced to 1-000, or even0998 ; but in these instances the worts must be ina proper state of dilution, and the ferment, or yeast,of the first quality.
UiiE mentions the works of a Scotch distiller, wherethe wash when let into the tun had a specific gravityof 1-0G5 to LOGO . The contents of the fermentingtun were 3000 gallons of wash, and the temperatureat the time of its introduction 64° to 74° Fahr. (17°-7to 23°-3 C.). Two gallons per cent, of barm wereadded, and the liquid agitated. When the attenua-tion had reached 1-04, another gallon per cent, ofbarm was added.
When the fermenting tuns are small, the tempera-ture of the worts should be higher than when thereverse is the case. Fermentation is proceedingfavourably if the bubbles of carbonic acid mount inrapid succession. Should the fermentation flag, itis almost a hopeless task to restore vigorous action.Some distillers try the addition of bubs — i.e., wortbrought into a rapid state of fermentation in a tubby a large portion of yeast; but this plan is seldomsuccessful. The law prohibits the addition of anywort after the expiration of twenty-four hours fromthe time the fermenting tun is charged, and if it beknown that after that time any has been added, thedistiller incurs a penalty.
With concentrated worts fermentation goes onbriskly for a short time, but after the alcohol hasaccumulated it lags, and no further addition of yeastwill revive it. The saccharine matter in such fer-mented worts possesses a highly disagreeable tasteand smell: hence the necessity of having themproperly diluted, as well as to avoid waste ofsaccharine matter. The worts, however, must not betoo dilute, as then fermentation ceases sooner, andthe diluted alcohol is more apt to run into the acetousfermentation. The attenuation is therefore urgedno longer than until the head of yeast falls, the dis-tiller thinking it more advantageous to neglect thematter remaining undecomposed, than to risk lossfrom the formation of vinegar. To prevent theheavy loss often incurred from this source, immediatedistillation of the fermented wort is generallyresorted to. Formation of vinegar is detected bythe increasing specific gravity of the worts, and thepeculiar aroma of acetic acid. It is, however, easilyguarded against; since if atmospheric air be excludedfrom the fermented liquor, no acetic acid is pro-duced. For this purpose the tuns are renderedair-tight by means of a well-fitting cover, throughwhich a large tube passes, and enters the bottom ofan open tub placed over the fermenting tun, which
in this instance is filled quite full; the rising barmand froth are forced through the pipe into the opentub, and when the fermentation slackens thesematters return into the tun. Many distillers usebutter to keep the wash from overflowing the tun.In general, the fermenting tuns are conical vessels ofmuch larger capacity than is required to hold thewash when first introduced, and thus serve thedouble purpose of containing the froth, and pre-venting the escape of the heat generated duringthe process.
At present, in the larger distilleries, the fermentingtuns are of iron, with an outer casing of wood.These are found to be much more easily managed thanthe wooden ones, the iron having a greater conductingpower. Should the heat of the wort get too high,cold water is introduced into the space between theenvelope and tun; and if it be too cold, it is readilybrought to the proper temperature by supplying thejacket with hot water.
Good attenuation is the desideratum, to the attain-ment of which the distiller’s attention is most parti-cularly directed.
In chemistry, by the term alcoholic fermentation isunderstood that change which sugar undergoes underthe influence of the yeast plant, and which pro-duces wine and all other alcoholic drinks. It servesas a type of a number of other analogous phenomenaknown by the generic term fermentation, but spe-cially designated by the name of the essential productof the particularplienomenon, as the panary, the lactic,the acetic fermentation, &c. The term alcoholic doesnot include all the phenomena of fermentation inwhich alcohol is produced, for many kinds have thatcommon character; but the words are used in thesense in which they have been applied by Lavoisier,Gay Lussac , Tiienard, and others, viz.: to designatethe fermentation of sugar with yeast.
The ordinary proposition, which is to be foundat the beginning of this article, that cane sugar(C 12 H 22 O n ) after being modified intogrape sugar(C 6 II 12 0 6 ) by absorption of water, splits up intoalcohol and carbonic acid, is according to Pas-teur really only a rough approximation to thetruth, although the sum of the weights of the alcoholand carbonic acid represents very nearly the weightof the sugar.
Pasteur’s researches prove that glycerine andsuccinic acid are also products of the alcoholic fer-mentation. Many methods may be used to provethe formation of succinic acid (C^IIgO^. One ofthe simplest is to evaporate the fermented liquidafter having filtered it to separate the yeast, andthen to heat the residue several times with ether,which is afterwards allowed to evaporate spon-taneously. In the course of a day or two the sidesof the glass are seen to be covered with crystals ofsuccinic acid. At the bottom is a syrupy liquid fullof the same crystals : this consists almost entirely ofglycerine saturated with succinic acid. This processis not admissible for extracting and estimating succinicacid,butwill serve to prove its presence in all fermentedliquors, whatever may be their nature and origin.