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A few cubic centimetres of sweetened yeast-water are put in it and boiled, so that the steam may destroy any germs adhering to the sides; and when cold the liquid is impregnated by means of a trace of pure yeast, introduced through the glass- stoppered tube.
The fermentable liquid was composed of yeast-water sweetened with 5 per cent, of sugar candy; the ferment employed was sacchormyces pastorianus. The impregnation took place on January 20th. January 21st. Fermentation commenced; a little frothy liquid issued from the escape tube and covered the mercury. The following days, fermentation was active.
If the yeast sown in the non-aerated fermentable liquid is in the least degree impure, especially if we use sweetened yeast-water, we may be sure that alcoholic fermentation will soon cease, if, indeed, it ever commences, and that accessory fermentations will go on. The vibrios of butyric fermentation, for instance, will propagate with remarkable facility under these circumstances.
The author has found, moreover, that the yeast of beer sown in an albuminous liquid, such as yeast-water, still multiplies, even when there is not a trace of sugar in the liquid, provided always that atmospheric oxygen is present in large quantities. When deprived of air, under these conditions, yeast does not germinate at all.
The three litres of yeast- water in the flask, supposing it to have been saturated, contains less than 16.5 cc. We shall better understand the significance of this result later on. Let us repeat the foregoing experiment, but under altered conditions. Let us fill, as before, our flask with sweetened yeast-water, but let this first be boiled, so as to expel all the air it contains.
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