Fermentation temperature rise

I have been hearing lately about fermenting at cool temperatures and then letting the temperature rise naturally once the bulk of the fermentation is complete. The idea is that the off flavors come from the yeast in the growth and active stage, so if you let the temp rise after that it helps it clean up without the off flavors. I think most of the discussions that I heard about this are from Brewing Network shows. I wanted to confirm what I heard so I did a search on this forum and couldn't find too much about it.

I am doing a pumpkin ale right now with Nottingham dry yeast. I held the temperature in my swamp cooler around 65 for about 3 days until I saw little activity in the airlock. Then I took it out of the cooler. I just checked it ( after 4 days) and the temp is up to 74. Is that too hot? Now I'm second guessing the technique since I couldn't find much info on it.

Thanks,
Tony.

It doesn't matter what your airlock does. It is a valve, a vent to release excess co2, NOT a calibrated fermentation gauge. If it is not bubbling it doesn't NEED to, not that, fermentation has stopped. You hydrometer proved that fermentation is going on. Get out of the habit of caring or worrying about what happens to your airlock, about half my beers never see a blip of an airlock. And I'm not the only one. You did good checking your gravity. That is what a hydrometer is best used for, a diagnostic tool.

You let your temps go high over a silly thing as airlock bubbling. Your beer should be fine, but next time keep your temps down and ignore your airlock.

I'm pretty sure it was Jamil Zainasheff who really recommended allowing the temperature to rise at the end of primary to make sure the yeast fully attenuate and to clean up any diacetyl.

The thing is, you still don't want to go over the yeast strain's temperature range.

For example, I like to ferment at the lower range of most ale yeast's optimum temperature. So, if I'm using Nottingham (57-70 degrees is the range, I believe) I'll ferment the beer at 60 degrees. Zainasheff recommends allowing the temperature to rise at the end of the primary, so after about 5 days of fermenting at 60, I would raise the temperature to 68 or so.

I don't always do that- it's hard to allow the temperature to rise without letting it rise to much with my set up. But that's the way I understand what he's recommending.

I think airlock activity is a pretty good indicator of when the fermentation begins to slow down, if you've had steady airlock activity.

I stuck it back in the cooler to try and get the temps down below 70. Hopefully the short time at 74 will not cause too much of a problem. Definitely going to invest in a chest freezer and temp controller so I can really control my fermentation temps!

Yeah, you are describing a diacetyl rest. The process as I recall JZ describing it is that he pitches a few degrees cooler than his desired fermentation temp. So he might pitch 1056 at 65 degrees and then let it naturally rise to 68 degrees and hold it there. (Again) as I recall, this is to maximize yeast vitality as the minor rise in temperature helps it get good and active and ready for a strong fermentation. I don't recall JZ saying he makes it regular practice to let the active fermentation raise for diacetyl rest...in fact I remember him saying the exact opposite, that he has found he doesn't need them because his process is providing him with excellent diacetyl free beer.

Bensiff said:

Yeah, you are describing a diacetyl rest. The process as I recall JZ describing it is that he pitches a few degrees cooler than his desired fermentation temp. So he might pitch 1056 at 65 degrees and then let it naturally rise to 68 degrees and hold it there. (Again) as I recall, this is to maximize yeast vitality as the minor rise in temperature helps it get good and active and ready for a strong fermentation. I don't recall JZ saying he makes it regular practice to let the active fermentation raise for diacetyl rest...in fact I remember him saying the exact opposite, that he has found he doesn't need them because his process is providing him with excellent diacetyl free beer.

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Right- I remember that too. And then, in a later podcast, he talked about this technique of fermenting in the cool range and then allow it to rise to the higher range (still in the optimum temperature range) at the end of fermentation. Not just for diacetyl (he admitted diacetyl is rarely a problem) but also to coax a few more attenuation points out of the yeast.

I specifically asked him about this when I saw him in June, and he said that is still his advice- ferment on the cool side of the yeast's range, and then finish it at a slightly higher temp, still in the yeast's optimum range.