Although cold Fermentation is deemed better for the quality of the beer, warm fermentation was often used in the production of dark lagers such as the infamous Bavarian Dunkel.

Warm Fermentation differs from the classic cold fermentation in that the target temperature is only held briefly before cooling begins.  The aim is to end the fermentation at cellar temperature for lagering so that some residual extract is left for secondary fermentation.  It’s important to avoid introducing yeast shocks due to temperature swings and it is, therefore, safer to begin cooling earlier rather than increase the cooling temperature. Temperature shocks are undesirable since they lead to low yeast concentration which negatively impacts secondary fermentation and conditioning. Again, the end temperature is very close to the same cellar temperature than in cold fermentation.

Here are the generally used temperature steps used in Warm Fermentation.

Step Temperature/°C
Pitch 7 – 8
Target 10 – 11
End 5 – 6

Here is a graph showing the primary warm fermentation cycle.

Once the end temperature is reached, we Germans say that the beer has attained “Schlauchreife” (don’t ask me to translate this).  This simply means it’s now ready to be transferred to the secondary Lager tank where fermentation and conditioning continue the same as for cold fermentation.

In the next section, it’s time to look at classic secondary fermentation — which is the same for cold and warm fermentation.