What is worse? High temperatures or temperature fluctuations?

Cheers,

It's getting hot with summer, but still I decided to give it a chance and brew a sweet stout, hopping that the taste of the brew would hide any off flavours due to high temps.

As air temperatures oscillates between 26ºC and 29ºC (some 79-84ºF), so to compensate I've put the bucket in a room with air conditioning, making the temperature of the brew drop to some 23.24ºC (some 73ºF).

Now, I feel like bubbling has stopped or considerabely slowed down, and I am concerned about the health of the yeast (Safale S-04). I've got some S-05 yeast and I am thinking to re-pitch some hopping to save the brew.

My questions are:

1. Is my yeast dead? Should I re-pitch or simply wait to make sure there is no more fermentation?
2. What should I have done? Simply let it ferment at high temperatures? Or was moving the yeast daily to an air conditioning room a good decision? Said in a different way, what hurts more the yeast and resulting beer, high temperatures or high changes of temperature?

Thanks for the potential answers.

Check the gravity, it might be done. If it's not done, it's probably stuck. If it's stuck, making a starter and repitching works well for me.

High temps will cause more off flavors. It's worse earlier in the fermentation than later.

Temp fluctuations increase the odds of a stuck fermentation.

You'll have to pick your poison.

Beernik said:

Check the gravity, it might be done. If it's not done, it's probably stuck. If it's stuck, making a starter and repitching works well for me.

High temps will cause more off flavors. It's worse earlier in the fermentation than later.

Temp fluctuations increase the odds of a stuck fermentation.

You'll have to pick your poison.

Click to expand...

As it's been fermenting only 3 days I am afraid it is stuck. I will give a try to gravity check and follow your advice.

I think next time my poison will be high temperatures instead of temp fluctuations

Thanks for your answer.

Fluctuations have a tendency to cause the yeast to stop. High temps cause off flavors. By the way, the temperature you're fermenting at in the air conditioned room is still pretty hot, and the temp of fermentation is going to be warmer than the ambient temperature. Anyway, at those temperatures, I'd be fairly sure that the yeast haven't died or quit early. In fact, they'll finish the job faster, and may be done in just a couple of days. I'd leave it in the fermenter for a minimum of 3 weeks though, just to be sure, and as Beernik said, check the gravity.