Fermentation temperature swings

Is it important to maintain a constant temperature during fermentation. My first batch has been fermenting for about 40 hours now. It started at 72F, I cooled it down to 62F, realized that was too cool and warmed it back up to 68F where it is now. I'm still learning ways to maintain the temp in my environment. Are these large swings in temp bad for the yeast or the fermentation process?

The yeast I'm using calls for 64-70F temps.

72 is on the warm side for most ale yeasts. Remember that fermentation creates additional heat. 62 is not too low. I do most of my ferments near 64 degrees, depending on the yeast.

I don't think that your temperature swings will have caused too much of a problem but it IS best to keep them to a minimum.

High temperatures induce the most flavor damage during the first couple days of fermentation.

petrolSpice said:

Are these large swings in temp bad for the yeast or the fermentation process?

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Yes. Those sorts of swings during active fermentation can stress the yeast and cause unwanted flavors. You would have been fine leaving it at 62.

It's easier to manage temps if you pitch cool, around 60-62*F and keep the beer temp on the low end of the range for that yeast for the first 3-5 days. The fermentation will then be less exothermic than if you pitch and/or ferment too warm.

BigFloyd said:

Yes. Those sorts of swings during active fermentation can stress the yeast and cause unwanted flavors. You would have been fine leaving it at 62.

It's easier to manage temps if you pitch cool, around 60-62*F and keep the beer temp on the low end of the range for that yeast for the first 3-5 days. The fermentation will then be less exothermic than if you pitch and/or ferment too warm.

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I think I pitched when the wort was too warm. I did not measure the temp before pitching, but the carboy was not warm to the touch. It's sitting at a steady 66F now.

A decent digital thermometer is an essential brewing tool. Search for "ES432" at Amazon for one less than $20.

BigFloyd said:

A decent digital thermometer is an essential brewing tool. Search for "ES432" at Amazon for one less than $20.

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or my new favorite . . .

The thermometer needs to be pretty long to reach the wort using a 6.5 gal carboy. A 12" stem would only stick about 4" into the wort, is that enough to get an accurate reading?

I want to get a thermometer to leave in the wort during fermentation. Those orange carboy caps with the thermowell, temp probe, and controller might work, but I heard the caps are not airtight most of the time.

You don't need a thermometer sticking into the middle of the fermentation. Measuring it on the side of the fermenter is just as good.

I was thinking more about checking the wort temp prior to pitching when I mentioned the need for a thermometer.

petrolSpice said:

I want to get a thermometer to leave in the wort during fermentation.

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Here's the Long-Stem Thermoworks in a 6.5 gallon carboy. The stem fit the small post on the carboy cap snuggly, but I used a hose clamp to be sure of a good seal.

BigFloyd said:

You don't need a thermometer sticking into the middle of the fermentation. Measuring it on the side of the fermenter is just as good.

I was thinking more about checking the wort temp prior to pitching when I mentioned the need for a thermometer.

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A couple (or more) brewers have used a thermowell and a fermometer or regular thermometer stuck to the side of the fermenter and have measured a difference...of about 1/2 to perhaps 1 whole degree. Not enough to worry about.

The swings in fermentation temperature are not important as long as you let it swing at the right time. Start the ferment at the low end of the yeast's preferred range and keep it there until the ferment slows, usually 3-4 days. At that point you can let it rise to the low to mid 70's and it will be fine. You don't want it too warm at the start because the yeast will heat it up even more and that is where you get the off flavors.