Measuring Fermentation Temperature in Air or Beer

My last few brews have come out rather estery and a bit reddish in color, which has been something of a disappointment. I'm trying to figure out the source of the issues, but I think that part of it is temperature control during fermentation.

I just went back to fermenting in a chest freezer around the time of the problems, so that's what I'm looking at. Here's my procedure for determining and setting fermentation temp. I'm using a standard chest freezer hooked up to a Ranco controller. The temperature probe is hanging freely inside the freezer.

1. Ferment a starter at room temperature (68-72 degrees, usually)
2. Look up ideal temp. range for yeast strain -- we use White Labs vials
3. Brew, rack, and pitch into glass carboy sitting on bare floor of chest freezer. Seal with three-piece airlock.
4. Set controller to bottom range of fermentation range with 2-3 degree differential.

I've always assumed that because the beer sits for so long in a sealed environment, it must reach equilibrium with the air around it. Perhaps that's not true? I know that yeast activity will generate a bit of heat. The brew tastes like it's fermenting too warm.

I've seen carboy stoppers with built-in thermowells, so I could drop the Ranco probe right down into the brew. Is this something to consider? Any advice would be hugely aprpeciated.

Food for thought - more often than not, the temperature inside the fermentor can be as much as 10 degrees warmer that the air temp outside during the peak of fermentation. For what it's worth, i set my chest freezer/controller for at least 5 degrees LOWER that my target ferment temp, and after the initial 3-5 days of vigorous ferment, bring it back up to where it "should" be.

10 degrees - no kidding!! So did you figure out the appropriate temp. by measuring something or another, or is it just clever use of trial and error?

It is going to take a lot longer for 5 gallons of wort to cool down than the air in the freezer. It will come to an equilibrium but only after fermentation is done and no exothermic reactions are happening.

You want to measure the temp of the beer not the air. As it stands now, you cool the air to the correct temp (your wort is a lot warmer) the wort warms the air back up pretty quickly, and then you keep repeating this. You need to get the beer down to temp you want, this will help stabilize the temp in the fermentor also. I bet your compressor kicks off and on pretty frequently?

You can get one of those termowells, but I have had good luck just sandwiching my temp probe between the glass of the fermentor and a 3/4 inch thick piece of neoprene (keyboard wrist pad) taped to the side. I keep the controller set for 1 degree diff and it still does not come on that often even in the peak of fermentation, but it does run longer when it does come on.

steelerguy said:

II have had good luck just sandwiching my temp probe between the glass of the fermentor and a 3/4 inch thick piece of neoprene (keyboard wrist pad) taped to the side. I keep the controller set for 1 degree diff and it still does not come on that often even in the peak of fermentation, but it does run longer when it does come on.

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+1 I use several layers of bubble wrap over the probe to insulate it from the air in order to read the temp of what's in the carboy.

I duct tape closed cell foam padding onto my glass carboy and slip the temp controller probe between the foam and the carboy. You'd be surprised how much heat a vigorous ferment gives off.