The phrase "clean up your beer" gets parroted ad nauseum but I don't understand how yeast sitting in a cake at the bottom of a fermenter are "cleaning up" anything.
There's only 10,000 threads discussing this already and where we have provided information about it. The yeast isn't as dormant and sitting in the bottom of the fermenter like everyone thinks...
For the sake of beating this horse to death, here's SOME of the primary source material that started me down this path 5 years ago, and HAS been posted ad nausuem on here.
Even John Palmer talks about this in How To Bew;
How To Brew said:
Leaving an ale beer in the primary fermentor for a total of 2-3 weeks (instead of just the one week most canned kits recommend), will provide time for the conditioning reactions and improve the beer. This extra time will also let more sediment settle out before bottling, resulting in a clearer beer and easier pouring. And, three weeks in the primary fermentor is usually not enough time for off-flavors to occur.
Also....
how to brew said:
The fermentation of malt sugars into beer is a complicated biochemical process. It is more than just the conversion of sugar to alcohol, which can be regarded as the primary activity. Total fermentation is better defined as three phases, the Adaptation or Lagtime phase, the Primary or Attenuative phase and a Secondary or Conditioning phase. The yeast do not end Phase 2 before beginning Phase 3, the processes occur in parallel, but the conditioning processes occur more slowly. As the majority of simple sugars are consumed, more and more of the yeast will transition to eating the larger, more complex sugars and early yeast by-products. This is why beer (and wine) improves with age to a degree, as long as they are on the yeast.
One of the compounds that it clears up in this time is diacetyl. , along with the benefits of letting a beer sit on the yeast cake a bit longer.
I found this article;
"THE ROLE OF DIACETYL IN BEER
By Moritz Kallmeyer"
The Abstract begins...
Diacetyl as a product of fermentation is more characteristic of ales than lagers. Diacetyl is produced early in the fermentation, and then most of it is reabsorbed by the yeast and reduced to flavourless compounds later on. Yeast strains differ markedly in their diacetyl reduction ability. Some ales and a few lagers (such as the famous Pilsner Urquell) contain perceptible amounts of diacetyl, but as a rule modern brewers consider it as a fault. This is because certain bacterial infections and other errors in brewing technique will increase diacetyl levels resulting in unacceptable beer aroma and flavour profile. This parameter thus serves as a quality check. However, it is important to remember that diacetyl flavour is a natural by-product of yeast fermentation, and in some beer styles it is an optional or even required flavour component in low amounts.
From here....
Drayman's Brewery and Distillery
There's two methods of rests listed in the Kallmeyer article...one for ales and warmer beers....interesting.
Maturation of beer flavour requires the presence of yeast as a catalyst. There are many methods of finishing that have the sole objective of prolonging the contact of beer with yeast after primary fermentation is completed. I want to emphasize that a diacetyl rest with most of the yeast lying at the bottom of the tank and not enough in suspension is of no use. Most lager breweries, especially those that use Weinhenstephan 308 or similar “diacetyl producing yeast’s” employ a long diacetyl rest, in order to minimize diacetyl in the finished beer.
Method 1
If a very cold primary fermentation was used it involves allowing the beer temperature to rise from the controlled primary fermentation temperature of about 10°C to 15-18°C when the primary fermentation is coming to an end. Normally, the time is determined by the attenuation of the beer. If, for example the wort starting gravity was 1050 and the expected terminal gravity is 1010, then the diacetyl rest would be commenced when the beer has attenuated to about SG 1023 when two-thirds of the total fermentable material in the wort has been consumed. The diacetyl rest normally lasts for 48-72 hours, until primary fermentation is over and secondary fermentation is under way. At this time the temperature is lowered when the more traditional method is followed, probably 1°C per day until the lagering temperature of 0-1°C is reached.
Method 2
If a warmer primary fermentation temperature was used for ale or lager the diacetyl rest involves either lowering the beer temperature 2 or 3°C at the end of primary fermentation or keeping it constant for up to 6 days. In lager yeast strains with low diacetyl production it is common practise nowadays to employ a short diacetyl rest followed by centrifuging to remove excess yeast and then crash cooling to 0°C. When brewing ales, that should have very low diacetyl levels especially German Ales like Alt and Kölsch, the implications are to not use highly flocculent yeast and to allow an extended primary fermentation, ....
All of this and everything else that could and has been said about this is in this thread here
https://www.homebrewtalk.com/f163/s...mil-zainasheff-weigh-176837/?highlight=palmer
I do believe that the OP stated THIS in his initial post???
I have my reasons to doubt this but I have stated them and won't bother rehashing theories.
And yet, we're rehasing theories...or I should say
you all are.
OOOH I just found a new one...too bad it's not animated.....
Edit One more thing you need to realize, there's going to be more and more info written about this stuff in the years to come, but it hasn't really been studied, because everyone JUST TOOK AUTOLYSIS AND GETTING IT OFF THE YEAST FOR GRANTED.
That's all we've heard....and like palmer said, even HE took it for granted.
I used to recommend racking a beer to a secondary fermenter. My recommendation was based on the premise that (20 years ago) larger (higher gravity) beers took longer to ferment completely, and that getting the beer off the yeast reduced the risk of yeast autolysis (ie., meaty or rubbery off-flavors) and it allowed more time for flocculation and clarification, reducing the amount of yeast and trub carryover to the bottle. Twenty years ago, a homebrewed beer typically had better flavor, or perhaps less risk of off-flavors, if it was racked off the trub and clarified before bottling. Today that is not the case.
Until WE came along....
we are the ones here who broke ground on this....it is because of our discussions over the last 4-5 years which forced questions to be asked, of Palmer, of BYP magazine and of Basic brewing.
In fact Palmer's "backpedaling" almost reads verbatum what I wrote, and other's on here as well. So it's clear that WE had a lot to do with this. And many of us took a lot of crap from folks...go back and look at some of the nastiness I took when I first started questioning the "common wisdom."
But a lot of the 'quantifying data" has yet to be written. It's still ancecdoatal, BUT now folks will look at it, and they WILL be able to tell you all about what your yeast is doing, hopefully to give make you all happy. But until then we have only our experinces, and our BJCP scoring sheets to back it up.
Something happens that DOESN'T happen when all we do is rack to a secondary...What we don't know yet....but something is. So that's why all we really have now is "Don't knock it til you try it." But enough people try it and don't go back....
So
maybe the whys will just have to wait.......
*shrug*
