When the saccharified wort obtained in the manner described has been cooled to about 15-20° and run into the fermenting vessels or " wash-backs," it is "pitched" with yeast to start the fermentation. Brewery yeast (top fermentation) is often used, but the best results are given with special distillery yeasts - that is, selected culture-yeasts adapted to distillery conditions. If pressed yeast is added, about 2 lb. are employed for every 100 gallons of wort. The usual practice, however, is to make what in this country is called "bub" - a small-scale preliminary fermentation in a good malt or malt and grain wort. This is "seeded" with the yeast and set to ferment a few hours before the main wort is ready for pitching; it provides a culture of vigorous young yeast-cells, and is added to the main wort in the proportion of 4 to 5 per cent.

It is important to check the growth of harmful bacteria in the early stages, as these organisms, by the subsidiary fermentations which they set up, both diminish the yield of alcohol and lower its quality. Generally, in the past, lactic acid has been used for this purpose, since a slightly acid wort tends to inhibit the bacterial development, whilst favouring the growth of the distillery yeast. The acid is produced in the separate small mash or "bub" by inoculating this, before adding yeast, with a pure culture of the lactic acid bacillus at a temperature of 50°. The acid itself eventually checks the growth and activity of the bacilli which produce it. The growing organism, however, should not be introduced into the main wort, there to rejuvenate itself and produce unnecessary acid. Hence its destruction is usually made certain by heating the bub to about 74°, after a sufficient acidity has been produced. When cooled, the mixture is seeded with yeast and fermented as already described.

Latterly, hotatier, the method most in favour for eliminating undesirable micro-organisms is the employment of antiseptics to which the selected yeast has been acclimatised. Thus small proportions of bismuth nitrate or calcium bisulphite have been used, but hydrofluoric acid or ammonium fluoride is now almost always chosen. The proportion of the acid employed is in general such as to give 0 005 per cent, of HF in the wort. This is reasonably effective against harmful bacteria, whereas yeasts can be accustomed to withstand forty times the amount. When such acclimatised yeasts and the fluorides are used, the previous saccharifica-tion of the starch by diastase can be carried out at the temperature, 55°, most favourable for the production of maltose (Effront's method).

In the early stage of the fermentation process there is a rapid development of the yeast, for which the best temperature is about 17-21°. The temperature rises as the operation proceeds, and the main fermentation occurs, in which the maltose and dextrose are transformed into alcohol; this goes on best at 26-30°. A secondary fermentation also ensues as the wort becomes warm, the diastase acting on any dextrins which remain, and gradually converting them more or less completely into fermentable sugars, to be promptly attacked by the yeast. During the early hours of the process, the ' wash " (as it is now termed) is roused to aerate it and expel the carbon dioxide formed, and the temperature of the wash is preferably not allowed to rise above 30°, at any stage. After about forty to forty-eight hours, the chief fermentation is over, and the wash has become "attenuated" down to a specific gravity approximating to that of water. It is kept for another day at 25-26°, by the end of which time the process is complete. The wash, when ready for distillation, contains usually about 12 per cent, or more of alcohol where the system of using concentrated worts is in practice, or from 4 1/2 to 7 1/2 per cent, where, as in most distilleries in this country, the wort before fermentation has a specific gravity of 1.030 to 1.055.

The fermentation of beet mashes, or of mixed beet and potato mashes, is carried out in Austria-Hungary as follows.1 With beet-mashes alone, beer yeast is sometimes used, the proportion being 15 to 20 litres of fresh yeast to each 1000 litres of the mash. After twenty-four hours, during which time about two-thirds of the sugar is fermented, a further quantity of fresh beet-mash is added, and fermentation continued to completion in another twenty-four hours. Culture-yeasts are, however, preferable to beer-yeasts, and the best results have been obtained with a pure culture wine-yeast capable of fermenting both sucr and raffinose sugars. This yeast is grown for twenty-four harscs in a portion of the beet-mash which has been acidified with sulphuric acid, sufficient to bring its total acidity to 07°, the temperature being kept below 30°. The partially fermented product is then mixed with fresh beet-mash, a portion of the latter, however, being reserved for growing the yeast to be used in the next day's mash. The temperature of the main mash is maintained at 29° for eight to ten hours, after which the temperature shows no tendency to rise. Fermentation is complete in twenty-four hours after mixing. It is immaterial whether the fermenting vats are closed or open, since there is little danger of infection. Working with the culture-yeast, the quantity of alcohol produced per 100 kilos, of sugar present is about 60.4 litres, whereas when beer-yeast is employed the yield is only 54 to 55 litres.

When both beets and potatoes (or maize) are used, the potato-(or maize-) mash is first fermented for twenty-four hours at a temperature not above 25°. At the end of this period, the beet-mash is well stirred in, and the fermentation allowed to proceed for another twenty-four hours, by which time it is complete.