According to the brewing institute at UC Davis and Jamil Zainachef, autolysis takes 4-8 months to take place. Autolysis is yeast cannibalizing as well as creating a hard cell wall and releasing unpleasant flavors into solution. The definition comes from both zymergy and "The Practical Brewer" which is a mediatory text book if you wish to get a brewing/microbiology degree from MBAA.
It used to be thought and taught that autolysis would take place within a month, so it was important to get the beer off the yeast cake as soon as primary fermentation was complete. That theory has been debunked by the UC Davis Brewer's guild as well as experts such as John Palmer, Zainachef, and Gordon Strong.
For prolonged aging of beer, racking to an aging vessel is still recommended, but it's not a secondary fermenter being that no fermentation will take place. The yeast has dropped out of suspension, and no more sugars will be consumed. Unless you add a second yeast strain, there will be no C02 build up in the conditioning vessel, so when moving from primary to secondary it's wise to purge the conditioning vessel with C02, and push the beer from primary to aging using C02. If a secondary fermentation is actually taking place, whereby a yeast strain is consuming additional sugars such as fruit or a lacto or pedio strain is being added then O2 must be present in the secondary fermenter. The sacchramyces will be either filtered out or dropped out using a cold room and gelatin. This is secondary, not conditioning. Conditioning is aging the beer to let more complex flavors meld, dry hops release beta acids for aroma, or a lagering process for clarity. The beer is racked off the yeast, but 80% of the yeast still makes into the conditioning vessel if you are not filtering prior to transferring. Whether you have minimal headspace or not in the conditioning vessel unless you push via C02 from the fermenter to the brite tank you are introducing O2. This is why the experts say to just leave the beer alone unless it's going to be aged for 6 months or more.
If aging and the use of a brite tank is being used, stainless conicals are recommended. They can be pressurized and the yeast run off without disturbing the beer.
It's important to note that one reason autolysis was debunked was because by racking your beer to secondary or removing the yeast slurry from a conical, you remove 20-30% of the dead yeast cells in the beer. 80% are still floating in solution, and won't be removed without the use of a .5 micron filter. 45% can be removed by cold crashing and gelatin, so when grad students and experts realized that they were leaving 45% of these so called harmful yeast in solution with no adverse affects, with the exception of oxidation, they furthered their studies perform research only on the autolysis myth. The same is being done with the hot side aeration theory.
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