After settling, the wort is again drawn off and the residue sparged. The hot wort is then cooled by passing over a large Baudelot cooler, or "beer fall," consisting of a series of copper pipes through which cold water or a solution from a refrigerating machine passes. The cooling is accompanied by aeration, which is very desirable ; but great care should be taken at this point to prevent infection by bacteria and other microorganisms from the air. Special devices to prevent this are in use in the most scientific breweries.
(3) Fermentation.
After proper cooling and aerating, the fresh wort is ready to pass to the fermenting tuns, and is inoculated with yeast or "pitched." In case pure cultures of yeast are not maintained for ferment ing, the yeast is frequently added to the wort in the pan at the base of the Baudelot cooler, and the whole mixed mass run through pipes to the fer menting room. When special pure cultures are employed, a "pure culture apparatus" is necessary. In this the yeast is developed, starting from a single cell, until sufficient has been prepared to "pitch" the whole volume of wort.
As has already been stated, the top fermentation is employed for ale, stout, porter, and Weiss beer, and the bottom fermentation for lager and Ameri can steam beer. Bottom fermentation proceeds at temperatures ranging from 42° to 51° Fahr., top fermentation at to Fahr. The control of temperatures in the fermenting cellar is therefore a matter of importance. The bottom fermentation proceeds somewhat the more slowly, requiring eight to fifteen or sixteen days, while top fermen tation is finished in a few days.
Fermentation may be regarded as occurring in two distinct stages: (1) The "primary" or "principal" fermentation, in which the maltose is especially acted on at tem peratures of to Fahr., for bottom yeasts, and 57' to Fahr., for top yeasts.
(2) The " secondary" or " after-fermentation," in which the malto-dextrin is transformed by bot tom yeasts at 34° to 37° Fahr., and by top yeasts at about Fahr. The yeasts used should in either case he freshly developed, free from contaminating organisms, and in actively growing condition. The amount added depends on a number of conditions, so that the experienced brewer uses his judgment rather than a definite rule.
The fermenting tuns are generally large wooden tanks (50-barrel capacity) in the form of a truncated cone, open at the top, and provided with a coil of pipe in the bottom to regulate temperature.
Bett,»11-fermentation beers.—In lager-beer mak ing, after the tanks are tilled with the freshly aerated, pitched wort, the fermentation sets in slowly at first. Within fifteen to twenty-four hours, small bubbles of gas appear around the the walls of the tank, and the whole surface is soon after covered with a fine white foam or froth. This gradually increases in amount, but remains thickest at the walls of the tank. When the foam becomes a certain depth, owing to the active fer mentation, a breaking up into rounded masses is seen, and a general movement from the walls toward the middle of the tank. This is known as the " Kraiisen " or "cauliflower" stage, from the resemblance of the masses of foam to heads of cauliflower. Two stages of " Kraiisen" are recog nized —" young Kraiisen" and "high Kraiisen." As a large amount of heat is developed by fer mentation, it is necessary to keep the solution dur ing this period down to about 50° Fahr. by means of the attemperators, and, as soon as the fermenta tion slackens in activity, the temperature is brought to 39' to 40° Fahr.
The whole period of fermentation is of eight to sixteen days' duration. During this time, the color of the beer deepens, and the suspended yeast and other materials should collect in little flecks, leav ing the beer perfectly clear. A large amount of yeast is developed during fermentation, as the sugar is transformed to alcohol and carbon dioxid. The carbon dioxid escapes as gas, displacing the air over the fermenting liquid in the vats. About one-fifth of one per cent remains in solution.
The amount of solids in solution is determined by an instrument known as a saccharometer. As fermentation proceeds the readings become less and less, showing the "attenuation" of the beer.
When the principal fermentation is at an end, the beer is practically ready for the storage vats, where it undergoes the secondary fermentation. During the primary fermentation the sugar is not all destroyed, and this residue of maltose and some of the malto-dextrin are now slowly acted on by the yeast, and eventually become very clear. The dura tion of storage depends on the destiny of the beer ; if for present use, a quick treatment with clarifica tion is employed ; if for export, a storage period varying from six weeks to three months follows.