Traditional European lager brewers, especially in Germany and Scandinavia, use starter tanks in which yeast is added to the cooled wort and the contents then allowed to stand for a period of up to 24 hours before racking (30). Traditionally, starter tanks were open vessels, but nowadays they are generally designed like regular closed-in fermenters.
Topping Up (Darauflassen)
If the brewer doesn't have enough yeast or if the brewer has a smaller mash tun and kettle than the fermenter, the brewer can employ a technique called topping up or darauflassen. Topping up, a technique common among German lager brewers, is the infusion of wort into a tank with strongly fermenting young beer (high kraeusen).
Traditional Lager Fermentation
While vertical cylindroconical fermenters are used to make the majority of the world's lager production, open square fermenters are still commonly used (especially in Eastern Europe) in traditional lager fermentation. In recent years, some major brewers have started fermenting their lagers in open square fermenters for quality reasons.
Modern Lager Fermentation
Today modern lager fermentation typically uses vertical cylindrodroconical fermenters achieving similar flavor profiles compared to traditional fermentation systems. In modern fermentation 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 (25). After 3 to 4 days, at peak fermentation, the fermentation temperature is allowed to ramp up in order to facilitate a rapid reduction in diacetyl. Some brewers use the same starting temperature for pitching but then increase the temperature between 14 and 15°C (24). Other breweries are known to pitch between 10 and 13°C and then increase the temperature to as high as 17°C, with a short diacetyl rest (28).
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