A very high temperature, as we have shown, kills the germs of disease in wine and beer. Extreme cold has the effect of indefinitely suspending the action of the ferment. A moderate temperature seems most favourable to the action of the organisms which work the wondrous changes in the wort. In England beer is usually fermented at a temperature of between 60° and 70° Fahr., and the process only lasts a day or two. In Germany the general practice is to ferment at about 40°, a temperature maintained by means of vessels containing ice, which are thrown into the fermenting tuns. This lower temperature checks the action of the ferment and the process lasts for fifteen or even twenty days.

The only other point to be noticed here in connection with fermentation is the peculiar fact discovered by Pasteur, that the organisms causing the ferment can live without air. When the wort is in the fermenting tun, the sides of the tun, together with the heavy carbonic acid gas hanging over the surface of the wort, exclude all air from the organisms, which can only obtain a small amount of oxygen from the liquid. There is, in fact, life without air. Pasteur made some interesting experiments which showed that there was a great difference in the action of the organisms according as they were placed in deep vats, cut off from the air by the carbonic acid gas, or in flat-bottomed {444} wooden troughs with sides a few inches high. In this latter situation the life of the ferment seemed enhanced, but the amount of sugar decomposed by the organisms was proportionately different from that decomposed in the vats. In the vats one ounce of ferment decomposed from seventy to a hundred and fifty ounces of sugar, while in the troughs the same quantity of ferment decomposed only five or six ounces of sugar. The experiment showed that the more the yeast was exposed to the air, the less was its power as a ferment, and that there is a remarkable relation between fermentation and life without air.

Dumas once said to Pasteur before the Academy of Sciences: “You have discovered a third kingdom—the kingdom to which those organisms belong which, with all the prerogatives of animal life, do not require air for their existence, and which find the heat that is necessary for them in the chemical decompositions which they set up around them.”

INDEX.

TRANSCRIBER’S NOTE.

Original spelling and grammar have been generally retained, with some exceptions noted below. Original printed page numbers are shown like this: {52}. Footnotes have been relabeled 1–75, and moved from within paragraphs to nearby locations between paragraphs. The transcriber produced the cover image and hereby assigns it to the public domain. Original page images are available from archive.org—search for “cu31924029894759”.

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