Bavarian brewers are of the opinion that larger surface area fermentation vessels deliver a finer product for their ales. Often these are open fermenters, i.e. not enclosed vessels and the head is regularly cropped off. Regular cropping indeed helps the fermentation a lot — and will yield a better tasting product. At 100 IBU the importance may be diminished, at 12 IBU the impact will be quite noticeable.
Using open fermenters requires the room temperature to be a little lower than pitching or fermentation temperature. Bavarian ale fermentations are conducted in a room temperature in the range of 12-15C (the actual temperature of the liquid will be higher due to the energy set free during the process). However in closed and temperature controlled fermenters, a range of 18-20C is perfectly adequate.
Pitching the yeast is done at slightly lower temperatures as well. For open vessels this is usually done in the 12-16C range. The traditional method is to subtract the room temperature of the fermentor from 30 in order to determine the pitching temperature. For e.g. at a cellar temperature of 18C the yeast is pitched at 12C. If Drauflassen is used, then this usually happens within 12 hours after fermentation begin [Narziss]. For higher fermentation temperatures, such as 23C, the pitching temperature sinks to 7C. Note that fermentation is an exothermic reaction and will heat up the liquid quite naturally. For smaller batches, I simply switch the heating element off for a couple of days and then back on so it can maintain the correct temperature until completion.
Skim, and skim plenty!
After fermentation begins, many by-products such as trub and resins are driven towards the surface (Hopfentrieb). It’s easy to detect the resinous excretion of the wort, which is now skimmed to achieve cleaner fermentation and a finer taste. This happens pretty much at high-kräusen.
Thereafter, the head is collapsing slightly and a creamy layer of yeast becomes visible. This is the best yeast to harvest, with the added benefit that it is now free of any resinous matter and won’t require washing. Again, another round of skimming begins. This time every 3-6 hours until fermentation is complete.
Once fermentation is complete, the beer is transferred to a lager tank and chilled for a couple of days (for larger vessels this will be weeks) at 4-7C to help the yeast drop out… some breweries may even go as far down as -2C.
Then the beer is bottled for final fermentation and conditioning using unfermented wort or Kräusen (i.e. wort at peak fermentation). Often this happens with injection of fresh yeast (0.1 %) for a better and more predictable result during the conditioning phase. This yeast is not necessary ale yeast. Many breweries use lager yeast for this purpose. I am a bit old-fashioned and use the same yeast all throughout. Another brewery famous for doing this is Schneider-Bräu in Kelheim.
To sum it all up, here is how I ferment pretty much all ales, such as Bavarian Wheat beers or English and Belgian styles:
- Decide on main fermentation temperature, subtract from 30 and cool the wort down to that temperature.
- Pitch yeast
- When working with a cyclonical fermenter, remove any trub via the bottom valve.
- 8-12 hours after pitching the “Hopfentrieb” occurs – it lasts 12-24 hours. This bitter and resinous layer is now skimmed.
- 24-36 hours after pitching the “Hefetrieb” occurs. This smeary cover of yeast is skimmed (and harvested) every 3-6 hours. Don’t let it go too thick!
- Once no gravity drop is registered for at least 36 hours, the beer is now transferred to a lager vessel and chilled to -2C for 2-3 days. This will really help it clear and allow the yeast to drop out even more proteins. Many british ale breweries also use this regime.
- You can re-use the yeast that dropped out at the bottom, but I found that the yeast harvested via the “Hefetrieb” is much fresher and more than enough for bottle conditioning and fermenting the next batch.