The determination of what is termed the " spirit indication " does not present great difficulty Graham, Hofmann, and Redwood have ascertained that a knowledge of the extract gravity and epirit indication of beer is sufficient to enable the original gravity to be determined with certainty.
The following tables were compiled to enable the original gravity of a beer to be determined from an observation of its spirit indication. These tables show the number of degrees of gravity lost by an ordinary malt wort corresponding to the different degrees of spirit indication, the first table being intended tbr use when this indication is obtained by the distillation process, and the second when it is obtained by the more practical process of evaporation. When the distillation process is used, a convenient quantity of beer is carefully measured in a glass flask, and then placed in a retort fitted with a tubular condenser.
Distillation is carried on until the whole of the alcohol is brought over, the alcohOl being r eceived in the flask in which the beer was originally measured. The alcohol collected is next ade up to the original bulk of the beer by the addition of water, and the ap. gr. of the liquid is then carefully observed at a temperature of 60° by the aid of the weighing bottle or a delicate hy drometer.
The number of degrees by which this specific gravity is less than that of water is the apirit indication.
The epirit indication may be more readily obtained by simply subtracting the beer gravity from the extract gravity, a radhod uaed by the German brewers. This is a more convenient method than the former, aince, to obtain the extract gravity, the beer Inas merely to be evaporated in an open flask, without collecting the apirit. In came where the spirit indication has been determined by the latter method, the sec,ond of the foregoing tablet) has to be used to ascertain the original gravity. Thus, if the spirit indication is 9° 6, and the extract gravity 1044.7, the original gravity will have been 1014'7 + 43 = 1087°7, for 43° is according to this table the loss of gravity corre sponding to a spirit indication of 9°6. It will be noticed that the tables do not exactly agree, for the spirit indication obtained from any given beer by the distillation process is always somewhat greater than that obtained by the other procesa. The reaeon of this is that when alcohol is added to pure water, the density of the mixture is lower than that of the water. An additioh of 8 per
cent., by weight, of alcohol, gives a mixture having a deneity of 586.7, which is a loss of gravity of 13°3 ; but 8 per cent. of alcohol in the same volume of water containing 10 per cent. of cane sugar, occasiona a loss of gravity of only 12° 92, or a reduction from 1036°47 to 1023°55. The degrees of epirit indication obtained are therefore less from the same abaolute quantity of spirit in the eugar solution than in pure water. The sugar solution containing alcohol represents the beer, and gives the loss of gravity which the beer austains by evaporation. On the other hand, the firat mixture of pure water and alcohol represents the dilute spirits obtained from the same beer by diatillation. The results are : Degrees of spirit indication .. 13.30 by distillation.
17 51 .. 12 -92 by evaporation.
Difference .. 0 . 38 Thus the addition of a certain proportion of akohol leaves the epecific gravity of the mixture a little higher when the water contains sugar in solution.
Fermentation demands the grcateat care of any atage in the brewing. process. Errors in malting or even in mashing, may be rectified; but a alight error in the fermentation process is attended with very serious results.
It was at one time the practice amongst the Scotch brewera to employ fermenting rounds only, and to cleanae from thew directly into the casks. The fermentation was completed in the rounds. Under this system the process of fermentation required from one to three weeks. The wort was usually pitched at a low temperature, 10° or 1I° (51° or 52° F.), and no more yeast was used than staictly necessary ; if the quantity first introduced failed to produce sufficiently active fermentation, the contents of the rounds were agitated twice daily, or a further quantity of yeast was added aud NMI stirred in whilst the fermentation was going on. The yeast formed was not skimmed off, and the fermentation was allowed to proceed until the ale waa reduced to about one-fourth of the original gravity. The attenuation proceeded so slowly at the completion of fermentation as not to eweed half a pound a day. For some days previous to the drawing off, the head of yeaat was not disturbed, and it floated on the surface as the ale was drawn off from below.