There's a lot of confusion and "mystique" around the subject of brewing lager-style beers. The process may vary from brewer to brewer but the principles are not all that complex when you break it down:
- Cooler fermentation generally yields less ester production, but in many yeast strains yields higher diacetyl production.
- Ester production happens early in the fermentation as a by-product of reproduction.
- Pitching a much higher yeast cell count limits reproduction and further inhibits ester production.
- Diacetyl produced at lower temps can be metabolized by yeast when sugar molecules as a food source become more scarce.
- Raising the temp to encourage yeast metabolism helps to remove diacetyl compounds from the finished beer.
- Lowering temp after full fermentation forces yeast activity to stop and inactive yeast drops to the bottom of the vessel.
- As yeast, proteins and other molecules and particulates drop out of suspension, they strip the beer of most remaining flavor compounds.
- In several weeks time in the low 30s, the beer has cleared about as much as it's going to and improvement is relatively minimal after that.
- Clearing and settling can happen in the bottle after carbing...there's just a little more yeast sediment at the bottom.
- Clearing of the beer can be accomplished or assisted by adding floculent or by filtering,
- All this assumes good sanitation, temperature control and minimal oxygen exposure at all stages of fermentation.
- Enjoy.
