What is happening during lagering?

[pietro]

I posted this awhile back on Stackexchange and did not get an answer. An answer that surpassed the vague nonsense of "it rounds the beer out" or "it helps to bring the flavors together", or "it mellows out".

I do understand that it can help to clear flocculated yeast, further it drops out polyphenols, including tannins. Though reading through some of kai's site, it sounds as though there is an actual fermentation happening during this step?

I know wort and more so beer are REALLY complicated soups of sugars, carbs, alcohol, proteins, and a bunch of other compounds that I forgot from sophomore year chem class. I thought I would put this question out to my favorite underground German brewing fundamentalists.

[Bryan R]

Traditionally yes, we call that the slow fermentation. Pretty much all that is used now-a-days is the accelerated fermentation. But a good number of "fest" beers are still produced the old way, involving krausening and yeast whispering.

Its all about trub, yeast and polyphenals dropping out, and of course when that happens flavors meld, and whatnot. Cold temperatures help precipitate those particles, and when you couple that with time, as with any beer (hopefully) the flavors meld, hops soften, and beers get great. Of course as you say there is a crazy amount of science behind that!

[Techbrau]

Like Bryan mentioned, broadly speaking there are two kinds of lager fermentations: traditional and modern.

Modern fermentation schedules rarely last more than 21 days including cold conditioning, and the primary ferment is over within 8-10 days. Typically the beer is fermented between 9C and 12C (depending on the strain), and yeast is pitched 2-3C lower than the intended fermentation temp. You can carry the whole fermentation through at one temperature, but commonly once the beer hits 50% EVG the temperature is raised to anywhere between 14 and 20 C to let the beer finish. Once final gravity is reached and the beer has matured (yeast has reabsorbed diacetyl, etc) the temperature is lowered to between -1 and 1.5 C for 10-14 days for the yeast and haze causing particulates to drop out.

In the traditional schedule, the yeast is pitched at 4-6 C and the beer fermented at 7-9 C. Once 50% EVG is reached, it is transferred to lagering tanks and very slowly cooled (less than 1 C per day). Fermentation continues during this long period of time, which can be as long as months. As the remaining sugar is being fermented, the yeast is simultaneously cleaning up green beer compounds like diacetyl. This schedule is quite difficult to pull off properly without stalling the yeast and getting an under attenuated beer.

[pietro]

So I guess to take the discussion a step further, do any German breweries still use the traditional method?

Has anyone on this forum done a side-by-side or blind triangle of identical worts fermented with these two different schedules?

Yet another subquestion: what does reinheitsgebot (and more importantly, those on this forum!) say about fining agents to assist in this process of dropping out unwanted compounds?

I have produced what to my palette (and in some cases, palettes of BJCP's, who obviously aren't the end-all/be-all) excellent lagers by pitching at 8-10*C, fermenting there for a week (roughly until 50% attenuation) raising to 15-16* for another week, then 18-20* C for another week, followed by a lagering period anywhere from .5-1 week per * Plato.

I don't know, however, if I have ever tasted a beer fermented the traditional way, so maybe I'm just living in a small universe.

[Bryan R]

I would say in Bavaria, yes.. But probably only for Fest biers( including to but not limited to Oktoberfest, Christmas, and other holiday beer type things).

Roachbrau is working on it, but the traditional takes a lot of time, you are looking at an easy 6 months. You have to know you yeast very well, as its very difficult to pull off properly.

You can fine with pvpp, but it has to be filtered or centrifuged out. PVPP is for polyphenols though and without getting out the yeast first it will actually hurt its effectiveness. The Germans are BIG on filtering.

Yup, thats the modern method ( which there can be variants of). It works as well.

[lhommedieu]

My next Marzen will be fermented at 50F until the residual sugar level is between 3%-4%, then lagered for seven months. This is a departure for me: despite lagering for several months in the past, my beer has been kegged when fermentation stops and forced carbonated. I hope that my new method will allow the beer to continue to slowly ferment in the keg and naturally carbonate.

[Techbrau]

Augustiner ferments using the modern schedule. They are one of the most highly regarded breweries in Bavaria.

There is some debate as to whether the traditional schedule leaves behind more byproducts like diacetyl. Low levels of such compounds - barely shy of the taste threshold - may contribute positively to beer flavor and mouthfeel.