Temperature variation during fermentation.

Hi.

We have stepped up the frequency of brewing. Back in the day we could use a spare BOD incubator whose declared temperature uniformity was ± 1 °C, set at 20 °C.

Since it could hold two carboys at best, we are now using as a fermentation chamber a small room with a minisplit air conditioner monitored with a SensorPush thermometer. Temperature fluctuates slightly across day and night, so in the end we conclude it has a variation of ± 2 °C with the extremes happening for short periods of time.

Right now the minisplit is set to 19 °C so temperature range varies from 17 to 21 °C. Is this variation acceptable, or are some off-flavors inevitable? Temperature is measured from air, is the beer temperature prone to the same changes or are they attenuated a little by the volume and specific heat of the wort?

If temperature control must be stricter, which is the usual solution to it? Is it enough to add an isolation layer to the room?

 

I wouldn't sweat a +/-2*C variation.

Can you perceive any off flavors? That would be my deciding factor.

 

Setting each fermentor in a tub of water would probably negate any temperature swings. The larger mass would keep the temperature of the fermentors stable.

 

Some IPAs fermented with Safale S-05 developed a cheesy flavor whose origin we are trying to figure out.

Interestingly, these days have been rainy and temperature variation was much lower. Dunno if it was a product of humid air having more "thermal inertia" than dry air but it is worth exploring. Maybe a humidifier in the fermentation chamber is a good idea.

 

I never got cheesy from US-05 even when I fermented hot and without temp. control and I did it a few times. The beers all turned out fine and we are talking mostly IPAs. But I would not exclude it...

Just wait a bit more and taste the beer after a couple of weeks. Take a gravity sample there. I would not worry about temp. variation as this will not ruin a beer.

 

Cheesy usually can be attributed to old hops. Might not be in your case, but it is a common cause of that off flavor.

 

Temp measured by air will increase your swings greatly. You'd probably see a much tighter gap if you can get a probe into the wort. I'd be very hesitant to see that swing to the top of the range for an IPA as the air temp will be lower than the wort temp at the height of fermentation. You could see an additional degree or three higher in the wort. That puts you in the range for fruity esters and diacetyl