Like lager brewers, some ale brewers initiate fermentation in starter tanks in which the residence time may be as short as 3 hours or as long as 36 hours (22).
Traditional Ale Fermentation
The brewing of traditional cask ale is fermented in shallow vessels that could be round, square or rectangular often referred by the type of fermentation system (e.g., Yorkshire square, the Burton Union, the ale top-skimming system, and the ale dropping system). The Burton Union system is now confined to a single brewery in Burton-on-Trent, and the Yorkshire square system is found in Yorkshire and Midland breweries.
Modern Ale Fermentation
Today modern ale fermentation typically uses vertical cylindrodroconical fermenters achieving similar flavor profiles compared to traditional fermentation systems. Typically, the yeast is pitched between 15 and 22°C, and the temperature is allowed to rise gently to 18 to 25°C, depending on the yeast strain (7). At the end of fermentation a diacetyl rest may be incorporated, although some popular ales (e.g., Irish stouts) have a perceptible diacetyl character that is are part of the flavor profile.
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