Raising the fermentation temp

[lyonst2]

Hi all,

I have noticed in a few places that recipies call for the fermentation temp to rise over the length of the fermentation. Why is this? I am currently brewing a red ale which is fermenting at 19c (32f). What are the benefits to be had from raising this a few degrees through the course of fermentation?


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[Jes2xu]

Following this as well!

As I understand it it does two things.

1)
Helps to reach full attenuation, while not effecting the flavour too much seeing as the bulk of fermentation ( and hence ester production ) has already happened at lower temps.

2)
Helps the yeast clean up after itself after fermentation of maltose is complete.


But I that is just what I have read, so let's wait for someone that actually knows what the heck they are talking about to tell me what I got wrong! Lol


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[raouliii]

Hi all,

I have noticed in a few places that recipies call for the fermentation temp to rise over the length of the fermentation. Why is this? I am currently brewing a red ale which is fermenting at 19c (32f). What are the benefits to be had from raising this a few degrees through the course of fermentation?


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Since 19c does not equal 32f, I'll assume that 19c is correct, since it equates with 66F, which is within ale fermentation temperature range.

Most commercial ale yeasts have published, recommended, fermentation temperature ranges, which fall between 55degF and 75degF.

In general, wort temperature at the low end of a yeast's range, during the early stages (first few days) of fermentation, promotes a clean lag phase, during which fewer byproducts are produced while the yeast are reproducing.

Increasing the liquid temperature towards the top of the yeast's range during the middle to end of fermentation, promotes full fermentation and clean-up of many of the byproducts produced earlier.

 

[WhamFish]

In general, wort temperature at the low end of a yeast's range, during the early stages (first few days) of fermentation, promotes a clean lag phase, during which fewer byproducts are produced while the yeast are reproducing.

Increasing the liquid temperature towards the top of the yeast's range during the middle to end of fermentation, promotes full fermentation and clean-up of many of the byproducts produced earlier.

This,

I'll add that I think of the fermentation as a multi-step process:

1)Lag phase-Pitching to hour 18-24
2)Active Krausen phase- Day 2-6 marked by vigorous activity and krausen
3)Waning Fermentation phase- Variable timing but marked by lower activity while fermentation finishes
4)Conditioning phase, yeast cleans up then flocculates

Generally the temp is allowed to increase slowly from 1-4 then at the end of 4 you bring the temp down. But you can run all sorts of temp profiles to achieve different results.

In Phase 1, much of the yeast character of a beer is developed (which will be different for each type of yeast), the degree of this character can be changed by pitching at higher or lower temps. lower temp= lower yeast character, higher temp= more yeast character.

In Phase 2, attenuation is occurring, you can promote the speed an efficiency of this by increasing the temp. Yeast character is still being developed though to a lesser extent so the higher temps will cause a change in this flavor profile. lower temp= slower fermentation and lower yeast character, higher temp= faster fermentation and more yeast chearacter.

In Phase 3, the very last bit of sugars are being fermented. Higher temp here can cause the yeast to ferment out sugars that would have otherwise been left unfermented, resulting in higher attenuation. Very few yeast derived flavor changes occur from raising temps at this stage relative to temp changes in the previous stages. Lower temp= lower attenuation, higher temp= higher attenuation.

In Phase 4, The yeast clean up esters, diacetyl, sulfer containing compounds ect. It makes sense that a warmer temp here would promote this as well but I generally just let this happen at whatever ambient temp is. This part happens over a 2-3 week period and honestly its been my experience that this occurs effectively at a range of temperatures and it is really more about time than anything.

Then cold crash, I lumped this into phase 4.

 

[Arrheinous]

Take a look at some of the Belgion/saison yeasts for an example of how dramatic temperature can be on the final product. These need to start high. And if you're using something like WLP565 (the Dupont strain) then it won't even finish up fermentation at 90F (32C).

 

[WhamFish]

I should add that the temp rises I'm referring to are all relative to the temp tolerance of the given yeast strain.

Also with reference to your red ale, I'd say that your pitch temp seems correct and I wouldn't change that. Letting it rise on its own in Phase 2 to say 22c then stay there till cold crash might increase the fruit character of the beer if thats something you are looking for.

 

[lyonst2]

"

Since 19c does not equal 32f, I'll assume that 19c is correct, since it equates with 66F, which is within ale fermentation temperature range."

Lol- yes, that is what I meant... Not sure what happened there.

Thanks for your excellent explanation.

 

[GRBC]

In Phase 4, The yeast clean up esters, diacetyl, sulfer containing compounds ect. It makes sense that a warmer temp here would promote this as well but I generally just let this happen at whatever ambient temp is. This part happens over a 2-3 week period and honestly its been my experience that this occurs effectively at a range of temperatures and it is really more about time than anything.

Then cold crash, I lumped this into phase 4.

It is my understanding that once fermentation is done, any "clean-up" metabolism of diacetyl, etc. happens in a day or so. I don't think it goes on for weeks.

 

[WhamFish]

Interesting, this may be true. I do feel that my brews improve over a couple of weeks of conditioning time though. Maybe the bulk of the cleanup happens quick then more slowly?