Lager Fermentation Period

Cali Co Brewing · Jan 29, 2021

Hi all - and happy Friday. I have a Czech premium lager that’s been going for 20 days now and it’s still fermenting. I did a diacetyl rest for a day thinking it would be coming to a close after 13 days since pitching, but the activity was so great that I thought it might be best to drop the temp back down and let it do it’s thing (been fermenting at about 50°F with WLP 800). Gravity after 13 days measured 1.030 and when I checked it yesterday (19 days after pitching) it was at 1.026.

My target final gravity is 1.012, but I did a decoction mash and got a much higher OG than anticipated. I was supposed to get a 1.050 OG, but it started out with 1.068. I assume some of the sugar there is going to be unfermentable given the mash schedule, but I’m not sure how much longer this is going to keep going. Krausen still looks healthy and the sample yesterday tasted and looked on point.

Has anyone done the decoction mash before and had similar results? How much more can I expect the gravity to drop?

HighVoltageMan! · Jan 29, 2021

I have never had a lager take that long, but if it's still going, let it go.

Even on a high gravity lager, you should see it get down to 1.015-1.018. The decoction mash isn't necessarily going to give you a higher or lower finish gravity, but it does often improve extract efficiency. Mash temperatures and time will affect that more. The slower fermentation is likely due to an under-pitch condition.

Does it taste sweet (it shouldn't be very sweet) Does it taste good? That's what really counts.

Donoroto · Jan 29, 2021

Yep, my vote is underpitch. How much yeast did you use for what size batch?

If I were making a 5-gallon batch I would use not less than 3 packs of yeast, maybe even 5.

But no worries: it will take a lot longer but come out just fine. Your diacetyl rest might be almost as long as the fermentation time, just be aware. And then there's the lagering time but that can be done in a keg.

Cali Co Brewing · Jan 29, 2021

HighVoltageMan! said:
I have never had a lager take that long, but if it's still going, let it go.

Even on a high gravity lager, you should see it get down to 1.015-1.018. The decoction mash isn't necessarily going to give you a higher or lower finish gravity, but it does often improve extract efficiency. Mash temperatures and time will affect that more. The slower fermentation is likely due to an under-pitch condition.

Does it taste sweet (it shouldn't be very sweet) Does it taste good? That's what really counts.

Yup - underpitched. Checking the White Labs site, it recommends 4 vials. Taste was great, not sweet. I’ll let the diacetyl rest go for 2 more days at 60 and then recheck and go from there.

Thanks for the feedback!