Observations re Fermentation Temperature

I have started getting more “scientific” about my homebrewing. Last fall I started paying more attention to water analysis and adjustments. This fall I purchased temperature control equipment, including a carboy/fermenter heater, a Johnson A419 controller, and a thermowell that allows for the insertion of the A419 temperature probe into the center of the fermenter. After a failed first attempt using the new gear (see my post titled “Help! Can I save this batch?”), I have a Russian Imperial Stout bubbling away in my fermenter. What surprised me is the significant difference between the ambient room temperature, and the temperature inside the fermenter. Throughout the first 36-40 hours of fermentation, the temperature inside the fermenter has consistently been 9-11 degrees higher than the room temperature. I knew the fermentation process produced heat. However, I did not expect, nor can I recall reading anything saying the difference would be so great. In the past, I had primarily used room temperature as my fermentation temperature, i.e., if the recipe called for fermentation at 68 degrees, I set the thermostat in the room to 68 degrees. Obviously, I was fermenting at too high a temperature, at least during the early fermentation period. I am interested to see how better temperature control impacts the finished product.

I’m interested to find out myself. I’ll be doing my first batch with temp control this weekend. Still trying to dial in the chamber, but I figure when I get some volume inside it will back and fourth a little less. I won’t be using a thermowell, but your post tells me I should lower my setpoint a few degrees. I set up a 7 cu ft chest freezer with a johnson digital in cooling mode, and put a 60w lightbulb inside. I’ve run it for a few days, and everytime I’ve gone into the basement the control reads 66 degrees, while my setpoint is 64. I think I’ll lower the wattage on the bulb, and see what happens.

Hmm, that seems a bit odd. I have never seen my chamber be more than my set temp. Most of the times it is 1 to 2 degrees below the set temp as the control unit waits until the set temp is exceeded and then it cools to 2 degrees below the set temp. I could only imagine it being higher if it were in heating mode.

I could be wrong but that has been my experience.

Just to be sure it is clear what I am saying, my fermenter sits on a desk in a small room in my basement. It is not in a refrigerator or otherwise insulated. The room has electric baseboard heaters that I can use to adjust the air temperature. I cooled my wort, pitched my yeast, and sealed up the fermenter. The initial temperature inside the fermenter, as read by the probe in the thermowell inserted into the center of the fermenter, was 67 degrees. The air temperature in the room, as shown on a regular digital thermometer I keep in the room, was 74 degrees. I left the room temperature over 70 degrees until fermentation had started. I then turned off the heat in the room. The temperature in the room began to drop. However, the temperature in the fermenter rose. After 24 hours, the fermenter was bubbling vigorously. The temperature inside the fermenter had risen to 74 degrees, while the temperature in the room had dropped to 63 degrees. It has now been a bit less than 48 hours. The bubbling has slowed somewhat, but is still strong. The temperature inside the fermenter is 72 and the air temperature in the room is 65. My target fermentation temperature is 68 degrees. I expect that in the next day or so, the temperature in the fermenter will drop below 68. The heater will then kick on, to maintain my 68 degree target.

Try having a small fan blowing on the side of the fermenter - it’ll help a little in controlling the temp. With really big beers, 10+F isn’t uncommon.

Wait a minute here…

So my $10 Home Depot indoor thermostat that says 63 ambient room temp and a carboy thermostat says 66/68 in the green and you are saying that it’s really 72-8x inside the carboy? BTW - I just have an IPA in my carboy. So maybe the 66/68 is the same as inside the carboy?

Sounds like on its own, the room would stay in the low 60’s most of the time? If it were me, I would leave the heat off completely and pitch the yeast in the high 50’s, let it come up slowly and try to keep the beer temp under 65-68 or so

[quote=“GarretD”]So maybe the 66/68 is the same as inside the carboy?[/quote]The temp on the outside of the fermenter is very close to the temp inside with the caveat that the stick-on thermometer isn’t insulated against the cooler ambient air and might be reading a little lower.

this is what i would do, though i like to pitch lows sixties versus high fifties. Ambient of low sixties sound pretty damn good. The whole idea of pitching at 70 plus temps is crazy to me.

Thank you all for the posts. I am finding the info very interesting. It appears that I have been fermenting warmer than I should. I brew primarily in the fall and winter specifically because the temperature in my basement is cool and easier to control. Next batch, I will start cool and keep it cool.

In terms of characteristics, how will warmer fermentation temperatures affect a beer (not crazy warm, maybe 5-6 degrees warmer than the ideal temperature)? In the past, my beer has sometimes come out thinner in body, and more bitter than intended. Could warmer fermentation temperatures cuase or contribute to these undesirable characteristics?