Yeast and lagering
There might already be a thread on this, but I haven't found it.
When you lager/cold-condition a beer, what are the yeast doing, assuming that you reduced diacetyl and acetaldehyde to acceptable levels before cooling the beer?
If I were to lager a beer for an extended period of time, would I want to filter it prior to lagering or post-lagering?
Whatever you do, you need to lager on a small amount of yeast. If you filter first, it would be the equivalent of storing beer in final package at low temperatures. It would change character, but ivariably not for the better.
If you believe some people, then long cold storage does not add anything to the flavour / quality of the beer. I, and many others beg to differ. The problem is that it costs a fortune to cold store for a long time, so a decision has to be made on economic grounds - getting the beer clear enough to filter, and clsoe enough to what you would really like it to taste like against teh sheer cost of tanks and refrigeration. Your call (it has to be yours - I doubt if a survy of you regular customers people would pay double or triple cost for subtle differences - but try it by all means
The yeast helps mop up oxygen, produces a few by products adding flavour and "absorbs" or changes a few flavours to less flavoursome products such as diacetyl to acetoin (I think I've got that reaction correct). Beware too much yeast as a large volume can start autolysing creating some spectacularly unpleasant flavours. But all of these reactions are at very slow rates at zero to minus 2 C. The most immediateely obvious aspect of cold storage is reduction in suspended yeast cell count and protein material, making filtration easier.
It's not just yeast lagering effects, you also have to think about all the trub, protein and chill haze material that you could potentially remove by lagering too.
Firstly it depends on the temperature you lager at. I believe lager yeast will still be able to ferment any residual sugars left in the wort at around 6 degrees, although it wont be a significant amount. At 0 degrees, this will be pretty much nil. Yeast left in suspension also helps to ad colour, a bit of flavour and can mop up any left over oxygen. In the flip side, dead yeast cells also can spoil the beer flavour and head retention.
Secondly, it does depend somewhat on fermenter shape and yeast strain but lagering for any length of time will help yeast fall out of suspension. When i start to lager (unitank operation) i crash the beer, let it sit for 24 hours then start yeasting off. After about a week the beer is pretty clear. I lagered a batch of beer for 6 months as a one off and i found it was really crisp, very clear but still had some yeast left in suspension - it's inevitable.
As for filtering, i'd do that as close as possible to packaging/dispense as possible. The longer you lager, the easier you'll find it to filter and you'll find that the beer will be more stable than if you did it vice-versa.
Hope this helps!
Thanks Dick -- That's the sort of info I'm looking for. Is there some resource/reference you know of that will explain in more geeky detail the reactions that are happening which create new flavors and remove old ones (I know about the diacetyl to acetoin, but not many others).
Originally Posted by dick murton
My understanding is that some of said reactions, such as conversion of alcohols into esters, have nothing to do with yeast and everything to do with time and temperature, thus they'll happen even in aging filtered beer.