Fermentation is the all important step of brewing. It involves pitching the yeast to the wort and letting the yeast do all the work under ideal conditions. The wort is allowed to cool and is transferred to the fermenters. The correct amount and type of yeast is added to the wort. Within the first twenty-four hours, foam (called kraeusen) will be produced as the yeast vigorously attacks the sugar. The yeast begins to multiply rapidly as it consumes the sugars and converts them into alcohol and carbon dioxide, which is used for carbonating the beer. The total length of fermentation should last for almost a week. During that time, the foam will diminish as the yeast depletes the sugar. Due to the expense of good quality yeast, the yeast from the fermenter can be collected for later reuse. If top-fermentation yeast was employed, then yeast can be removed from the top by a skimmer. If bottom-fermentation yeast was put to use, then the yeast can be found at the bottom of the fermenter and drained. However, repetition of this practice degrades the yeast until a new stock must be used.
Depiicted below is a heat exchanger used to cool the hot wort from the boiler enroute to the fermenter.
Below is a picture of a 14 barrel fermenter with a small heat exchanger nearby. The cooled wort and yeast are introduced from the top of the fermenter. Valves at the bottom of the fermenter allow for the separate collection of bottom-fermenting yeast and the beer.
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