Chapter I

. It may be questioned whether the spontaneous yeast employed in the first brewery, or that which a wort left to itself in the present day would yield, would be of the “high” or “low” type. It may be concluded from what we have said on the subject of spontaneous fermentations in wort, that wort, left to itself, would furnish ferments more or less resembling those of wine. We have never obtained in spontaneous fermentations of wort either a distinctly “high” ferment, or a distinctly “low” one, properly so called; nor, further, have we ever obtained either one of these distinct kinds, with its industrial characteristics, in experiments on the ferments of fruits. What, then, was the origin of the “high” and “low” ferments now used by brewers? What was the nature of their original germs? These are questions which we are unable to answer, but we are very much inclined to think that we have here another example of the modifications which plants as well as races of animals undergo, and which become hereditary in the course of prolonged domestication. We know nothing of corn in its wild state, we cannot tell what its first grain was like. We know nothing of the silk-worm in its original state, and we are ignorant of the characters of the race that furnished the first egg.

These reflections may seem to favour the supposition that there is a real difference between “high” yeast and “low” yeast, and that both of these differ from spontaneous ferments and the ferments of domestic fruits. These are propositions demanding most careful consideration, for it is generally admitted that these ferments become intermixed, that their morphological differences are merely a question of medium, and that the transition of one to the other is a simple matter. The following facts seem to contradict such statements.

[Illustration: Fig. 39.]

“High” Ferment.—Fig. 39 represents some “high” yeast taken from a deposit after fermentation, and Fig. 40 the same yeast in course of propagation in some aerated wort. In comparing “high” yeast with other alcoholic ferments at the same stage of development, there are three points which are especially striking: the diameter of its cells is relatively large, their general aspect is rounder, and when they are undergoing propagation their mode of budding produces a markedly ramified appearance, so that the cells always occur in clusters and branches. Fig. 40 gives a very exact idea of these characters. To investigate satisfactorily the branching habit of growth peculiar to this ferment we should examine it during the first few hours of its propagation, when, under the influence of the oxygen dissolved in the fermentable liquid, its vital activity is greatest. Later on, often on the day following the sowing, the groups become disconnected, and at the end of the fermentation the cells have quite separated from each other, not more than 2 or 3 per cent. remaining united, and even these in groups of not more than two cells together. This is represented in Fig. 39.

To give an idea of the rapidity with which this ferment multiplies, we may state that our sketch (Fig. 40) was made under the following conditions:—On April 28th, 1874, we caused a flask of wort to ferment by means of a trace of “high” yeast. On the morning of the next day, that is fourteen hours afterwards, an appreciable deposit of yeast had formed, and some frothy patches appeared on the surface of the liquid, showing that fermentation had set in. On May 1st we decanted the beer, substituting for it water sweetened with 10 per cent. of sugar. On May 2nd we decanted the sweetened water, and substituted a fresh quantity containing the same percentage of sugar. On May 3rd, at mid-day, we took some of the fermenting liquid from this flask and put it into a flask of wort; five hours after the introduction of the ferment we made the sketch in question. The field is covered with branching clusters, the groups being sketched exactly as they occurred in the field. Their

## activity was due to the condition of the ferment, and to the perfect

fitness of the nutritive medium for its vegetation. In sweetened water the budding of the cells was considerably less active; no branching groups of cells are to be found. Budding, nevertheless, occurs to a considerable extent, but it is limited to one bud, or two at the most, to each cell. Fermentation in pure sweetened water is mostly correlative with the duration of vital activity in the globules already formed.

[Illustration: Fig. 40.]

Let us next suffer our yeast to exhaust itself by keeping it in a great excess of sweetened water for a very long time; we shall then be able to observe its process of revival, and see if we can find any facts analogous to those presented by _saccharomyces pastorianus_ (