I’ve been thinking a lot lately about what goes on during the aging/conditioning of ales, specifically the period between the end of complete primary fermentation (as defined by SG stability) and final packaging (either in a bottle or sealed, chilled and carbonated keg).
Correct the following if I have it wrong, please, and add anything you think relevant to improve my understanding.
An advantage of conditioning would be diacetyl reduction by the yeast that are still alive although metabolizing at a greatly reduced rate, “scrubbing” the beer of any remaining compounds they can digest. Cellaring temperatures (50’s) are preferred over serving temperatures (30-40’s) because yeast metabolism rates will be greater at the higher temperatures and so the conditioning process will proceed more quickly.
The vessel in which the beer is conditioned (glass carboy or steel keg) does not need an airlock to benefit the yeast. A steel keg could be purged with CO2 and sealed. A glass carboy needs an airlock to release the slow CO2 pressure build-up from the very slow yeast respiration, but this release of gas is not a necessary component of the environment the yeast need. The yeast don’t need to “breath”, rather the airlock just keeps the bung from being expelled from the carboy.
By extension, the same concepts apply to lagers. More time is required for conditioning because the lager yeast are working more slowly at colder temperatures.
Am I getting close to understanding this?