Here we have an explanation of the term “_high_ fermentation,” which has been applied to the foregoing process. This process is conducted at a high temperature, which, commencing at 19° C. or 20° C. (66° F. or 68° F.), is raised to 20° C. or 21° C. (68° or 70° F.) by the action of fermentation, which is always accompanied by an increase of heat.[6]
This is not, however, the only reason for the use of the term “_high_ fermentation.” We have just seen that the fermenting casks were so arranged that most of the yeast produced during the process of fermentation would rise to the upper part of the casks and work out of the bung-holes. In this practical fact we have the actual origin of the expressions “_high fermentation_” and “_high beer_,” which are used to distinguish this peculiar fermentation and the quality of beer derived from it.
As we have already observed, all beer was formerly produced by this mode of fermentation, which even at the present time is still practised in the breweries of Great Britain, where beer fermented at a low temperature is absolutely unknown.
“Low fermentation” is a slow process, effected at a low temperature, during which the yeast sinks to the bottom of the vats or casks. The wort, after cooling, is run into open wooden vats. In cooling, the wort is brought to as low a temperature as 8° C. (47° F.), or even 6° C. (43° F.), at which point it is maintained by cones or cylinders (styled _nageurs_, i.e., floats, by the French) floating in the fermenting vats. These floats may be filled with ice if the outside temperature requires it, as is invariably the case in summer.
The duration of this fermentation is ten, fifteen, or even twenty days. The yeast, which is produced less abundantly than in the case of beer fermented at a high temperature, is gathered after the beer has been drawn off, and is partly used in subsequent fermentations.
The term “_low_ fermentation” is derived partly from the lowness of the temperature during the fermenting process, and partly from the fact that the yeast is gathered at the bottom, and not at the upper part of the fermenting vessels.[7]
Beer fermented at a low temperature, of which there are several varieties, differing in colour and quality, is of Bavarian origin.[8] The preference of the public for this kind of beer, and the increased facilities that such a beer affords the trade, are the two reasons why its manufacture has so greatly increased. In Austria, Bavaria, Prussia, and other Continental countries this new method of brewing is almost exclusively adopted.