Traditional European lager brewers, especially in Germany and Scandinavia, use starter tanks to add yeast to the cooled wort. The contents are then allowed to stand for up to 24 hours before racking. Traditionally, starter tanks were open vessels, but nowadays they are generally designed as closed fermenters.
Topping Up (Darauflassen)
If the brewer doesn’t have enough yeast or if the mash tun and kettle are smaller than the fermenter, a technique called topping up or darauflassen can be employed. Topping up is a common technique among German lager brewers, where wort is infused into a tank with strongly fermenting young beer (high kraeusen).
Traditional Lager Fermentation
While vertical cylindroconical fermenters are used for the majority of lager production worldwide, open square fermenters are still commonly used in traditional lager fermentation, especially in Eastern Europe. In recent years, some major brewers have started fermenting their lagers in open square fermenters for quality reasons.
Modern Lager Fermentation
Modern lager fermentation typically utilizes vertical cylindroconical fermenters to achieve similar flavor profiles compared to traditional systems. In modern systems, the yeast is pitched at higher temperatures between 7 and 8°C, and after a couple of days, the temperature is increased to 10 to 11°C. After 3 to 4 days, at peak fermentation, the temperature is allowed to ramp up to facilitate a rapid reduction in diacetyl.
Similar to lager brewers, some ale brewers initiate fermentation in starter tanks, with residence times ranging from as short as 3 hours to as long as 36 hours.
Traditional Ale Fermentation
Traditional cask ale is fermented in shallow vessels, which can be round, square, or rectangular, often referred to by the type of fermentation system.
Modern Ale Fermentation
Modern ale fermentation typically uses vertical cylindroconical fermenters to achieve similar flavor profiles compared to traditional systems. The yeast is usually pitched between 15 and 22°C, and the temperature is allowed to gently rise to 18 to 25°C, depending on the yeast strain. 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 contributes to the flavor profile.