Stuck fermentation or just high gravity?!

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Well-Known Member
Apr 1, 2013
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Cape Town
I experimented with my own recipe (perhaps I should have got more experience before doing so):
  • 5 kg pilser, + 250 grams chocolate malt.
  • I heated my strike water to 80 celsius and mashed for 60 minutes. From 20 litres of strike water I got 16l. I sparged in two steps with 21 litres and got a further 16l from that (I am trying to get a light beer). So 32l in the pot.
  • I boiled for 60 and got 23.5l in the fermenter and probably lost about 2 litres during the siphon and to what was left in the pot.
  • I pitched one bag of Saflager 34/70 directly into the wort.
  • I ran the recipe through and get an estimated final gravity of 1.016 -1.011.

Within about 24 hours after pitching there was good activity in the airlock and this continued for another 48 hours. I kept the temp around 12 celsius. Then after another 12 hours the activity slowed, another 12 hours and it stopped completely and then there wasn't even any pressure showing in the airlock.

So I ramped the temp to 17 degrees and immediately (within a few hours) noticed pressure in the airlock. I then roused the yeast and about 12 hours later there were bubbles again - BUT much, much slower than when fermentation first took off. I pitched on 1 July.

I tried lowering the temperature again to 12 celsius as that appears to be the agreed optimal temp but things slowed down again. I am now raising the temp and will try keep it around 15 celsius, maybe a bit higher. I have noticed slightly more activity in the airlock since it is higher.

I have taken gravity readings for a few days now (10 July) and it is stuck at 1.017 - not horrendously far out of range, but out of range… or is it with the higher mash temp?

Two questions I would really appreciate help with:
  • could my high mash temp be pushing the final gravity higher and therefore 1.017 is actually on target? Or could I have a stuck fermentation?
  • I understand the airlock is meant to lock air out and not be used as a gauge…but I can’t help but think the difference in activity at different temperatures is saying something even though gravity measures aren’t….or isn’t it?

oh and by the way, the beer tastes fliiiiipn good already.
1.016 vs. 1.017 is nothin'. I'd call it done, especially since it tastes good. But yes, a higher mash temp can lead to a higher finishing gravity. Leave it for a couple weeks to settle/clean up, and it'll be great. Cheers!