Author Topic: During fermentation: Keep same temperature or slowly increase?  (Read 3676 times)

Offline wolfsong

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New(er) brewer here -

Most of what I've read says to keep the same temperature throughout fermentation. Which temperature used, depends on the yeast, ale/lager, etc.

Recently, I've come across people using fermentation temperature profiles where they slowly increase the fermentation temperature x degrees after n days.
Are these profiles a topic that some people swear by and other people don't see the need for?

I have two beers now fermenting, and I'm wondering whether to keep the current temperature or follow some existing profile (which profile though, I have no idea...).  My default is to keep them in fermenter for 3-4 weeks at a constant temperature, then bottle.

Saison: currently 8 days at 74 degrees. Yeast: Belle Saison.
Red Ale: currently 6 days at 65 degrees. Yeast: Safale S-04.

Thoughts or rationale one way or another, to keep same temperature or slowly increase the temperature?


Offline Scott Ickes

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Re: During fermentation: Keep same temperature or slowly increase?
« Reply #1 on: June 16, 2016, 12:19:22 PM »
I'm not sure of the chemistry of how and why it works, but increasing the temperature when the primary fermentation is almost finished allows the yeast to clean up some undesirable chemical compounds created during primary fermentation.  This is called a diacetyl rest.  The yeast become more active at the higher temperature and metabolize the diacetyl.  It gives you cleaner flavor profiles in the finished beer.  Diacetyl has buttery or butterscotch flavors that are inappropriate in most beer styles.  It's an extremely important step to take when making lagers, where diacetyl is very noticeable when present in the finished beer.

When my primary is about 90% complete, I raise the temperature about 5F and let it finish out at that temperature, until it starts to settle out and clear.  Then I lower the temperature down below my original primary fermentation temperature.  Let's say that I made the Red Ale that you made and fermented it at 65F.  At about day 4 (this would depend on how quickly the yeast consumed the sugars and could be needed sooner or later than 4 days), I would raise the temperature up to about 70F and let it sit there for about a week.  Then I would lower it to about 60F so that it can settle out and clear nicely before kegging or bottling.

Diacetyl is one of the most common faults pointed out by judges at brewing competitions.
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Scott Ickes


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Re: During fermentation: Keep same temperature or slowly increase?
« Reply #2 on: June 18, 2016, 01:01:16 PM »
I have to agree with Scott.  However, I like to gradually raise the temperature of my fermentation toward the end, particularly when I'm trying to get some of the esters out of the yeast.  As they say: "The brewer makes the wort, but its the yeast that makes the beer".  So allowing the fermentation temperature to raise slightly (5-100 F) will not only provide a diacetyl rest, it will also work the yeast into making some flavors needed, and expected, in some styles.