During Lagering, does yeast continue to ferment?

[DiscoRick]

I have looked all over the net and kind find the answer. Does yeast continue to ferment during the lagering process or does it go dormant?

I was just curious if I could expect any change in alcohol content post lagering.

 

[McKnuckle]

If it has not completely finished fermenting, then yes, it will, albeit slowly. The temperature has to be "not super cold" however.

I know this because I recently put a kegged lager in the relative cold (40ºF) before it was completely attenuated. It had been a pressure fermentation, and I thought for some reason that the yeast had given up, as FG was stable over a couple of days. I was wrong!

Over a period of one month, the beer absolutely continued to ferment, resulting in excessive foam when poured and some reluctance to clear. Once it was finally finished, the beer cleared perfectly and the carbonation evened out. The flavor also became stunningly clean, whereas before it had some flavors which I wrongly attributed to the malt but which in hindsight were clearly yeast-derived.

Now, if you drop the temp below where the yeast can be viable, I assume this would not occur. It's temperature dependent. So maybe my answer/experience does not apply to you.

 

[DiscoRick]

If it has not completely finished fermenting, then yes, it will, albeit slowly. The temperature has to be "not super cold" however.

I know this because I recently put a kegged lager in the relative cold (40ºF) before it was completely attenuated. It had been a pressure fermentation, and I thought for some reason that the yeast had given up, as FG was stable over a couple of days. I was wrong!

Over a period of one month, the beer absolutely continued to ferment, resulting in excessive foam when poured and some reluctance to clear. Once it was finally finished, the beer cleared perfectly and the carbonation evened out. The flavor also became stunningly clean, whereas before it had some flavors which I wrongly attributed to the malt but which in hindsight were clearly yeast-derived.

Now, if you drop the temp below where the yeast can be viable, I assume this would not occur. It's temperature dependent. So maybe my answer/experience does not apply to you.

Thanks for the answer. That's sort of what I expected would happen. Like you, I was suspicious my beer had not completely attenuated even though it was at the same FG over several days but it tasted a tad sweet. Well, I guess we'll see how it turns out. Thanks again!

 

[DiscoRick]

If it has not completely finished fermenting, then yes, it will, albeit slowly. The temperature has to be "not super cold" however.

I know this because I recently put a kegged lager in the relative cold (40ºF) before it was completely attenuated. It had been a pressure fermentation, and I thought for some reason that the yeast had given up, as FG was stable over a couple of days. I was wrong!

Over a period of one month, the beer absolutely continued to ferment, resulting in excessive foam when poured and some reluctance to clear. Once it was finally finished, the beer cleared perfectly and the carbonation evened out. The flavor also became stunningly clean, whereas before it had some flavors which I wrongly attributed to the malt but which in hindsight were clearly yeast-derived.

Now, if you drop the temp below where the yeast can be viable, I assume this would not occur. It's temperature dependent. So maybe my answer/experience does not apply to you.

That sort of brings up another question, at what temperature is lager yeast no longer viable for fermentation? I imagine this is strain dependent, but is there a bottom line temperature for all lager yeasts?

 

[McKnuckle]

If you haven't explored Braukaiser's site, it's an interesting read. Here is the section on lager fermentation. Pay attention to "The conventional fermentation in a German lager brewery" because it discusses how I, and perhaps you, inadvertently approached this! (i.e. extended, slow fermentation during lagering)

 

[Vale71]

That sort of brings up another question, at what temperature is lager yeast no longer viable for fermentation? I imagine this is strain dependent, but is there a bottom line temperature for all lager yeasts?

When beer starts to freeze. I'm not joking.
Though metabolism gets reeeeeally slow as you approach that point so that it might take a long time to see any appreciable change in attenuation. And some very sensitive equipment too, something better than a $5.00 hydrometer.

 

[DiscoRick]

If it has not completely finished fermenting, then yes, it will, albeit slowly. The temperature has to be "not super cold" however.

I know this because I recently put a kegged lager in the relative cold (40ºF) before it was completely attenuated. It had been a pressure fermentation, and I thought for some reason that the yeast had given up, as FG was stable over a couple of days. I was wrong!

Over a period of one month, the beer absolutely continued to ferment, resulting in excessive foam when poured and some reluctance to clear. Once it was finally finished, the beer cleared perfectly and the carbonation evened out. The flavor also became stunningly clean, whereas before it had some flavors which I wrongly attributed to the malt but which in hindsight were clearly yeast-derived.

Now, if you drop the temp below where the yeast can be viable, I assume this would not occur. It's temperature dependent. So maybe my answer/experience does not apply to you.

That website is a great reference tool! Thanks so much.

 

[DiscoRick]

When beer starts to freeze. I'm not joking.
Though metabolism gets reeeeeally slow as you approach that point so that it might take a long time to see any appreciable change in attenuation. And some very sensitive equipment too, something better than a $5.00 hydrometer.

Thanks for the reply. Well, I'll see how it goes I have it at 36 degrees right now. I could always ramp it up a few degrees I imagine.

 

[Tobor_8thMan]

I cold condition everything at 36 to 38F before putting into a keg for tapping.

I too was surprised as the FG goes down (meaning yeast are continuing to ferment). Doesn't matter if it's a lager or ale yeast, same results. I know the FG is different as I brew 11.5 gallons, do primary and then split into SS brew buckets. Say I keg one of the 5 gallons in May. Then, in November, I keg the other 5 gallons. The November FG is lower than the May FG. (Once again, "May" and "November" are only used as examples.)