I use a chest freezer with a Brewpad heating element stuck to the inside wall (for warmer fermentations/bottle conditioning), and a single-stage Johnson controller. Since getting this, I haven't used the freezer's compressor to cool the chamber, only the heating element, as ambient temps in my basement have been in the low 60's, and I haven't done any lagers or overly cold fermentations (yet). I have my temp controller probe taped to the outside of an Ale Pail/carboy, insulated by scrap styrofoam. However, since we had a non-winter in Maryland and it is getting warmer, my basement is now right around 70 degrees.

I switched the jumpers on my controller to a 'cooling' setup ("cut-out at setpoint"). Just last night, I made an extract stout that I want to ferment at 67 degrees. After getting the temperature inside the chest to around 67, I taped the probe onto the fermenter and went to bed. checked this morning and both the ambient temp of the freezer and the fermenter read 67 degrees. However, I went home for lunch, and the ambient temp was down to 58 degrees (!), with the fermenter temp holding at 68. My question is, with huge swings like this, won't the ambient temp ultimately bring down the fermenter temp even if the controller is 'not trying to', when the walls of the freezer are cold from the compressor, and the chest is sealed shut and providing insulation?

I understand that fermentation (active signs this morning and this afternoon) can create some decent heat from the anaerobic reactions, but is there a way to control this to a greater extent, or does it matter?

My other question is how/if anyone manages moisture inside a chest freezer fermentation chamber set up. Even with minimal compressor activity, it has kicked up quite a bit of humidity inside.


2 Answers 2


You are doing the right thing. Ambient temperature (aka the air temperature inside the chest) can go low like this, but since the probe is taped to the fermentation vessel, and the controller is calling for chilling, then chilling is what is needed. The thermal mass of the chest walls, cooling tubes, freon, and the air in the chest all might be below your target temperature, but the beer also has a large thermal mass that takes a while to move. I think you will find that you will not overshoot below your setpoint very much, if at all.

As for the humidity, routing your blowoff tube outside the chest would help considerably, but requires drilling a hole where you won't hit any vital components. You may also use a Damp-Rid style product. The crystals can be dried in the oven and re-used.

  • upvoted and accepted, thanks! If this ale weren't a brown ale disaster on the hot side that should've been a stout, I would offer to send you one! At least I know I won't have unwanted esters/phenols.
    – Pietro
    Commented Mar 23, 2012 at 1:00

Adding a computer fan inside my chest freezer really helped with the humidity issues. I use one of these USB fans. It has a flat cable so it fits fine in the closed door with no need to drill a hole anywhere. Also they're much worse in the warmer months when there's more humidity in the air and haven't been a problem when it's cooler outside. In the summer I occasionally mop the bottom with a towel that I hold onto with a pair of long bbq tongs. Haven't needed the Damp Rid, though lots of people recommend it. Damp Rid is calcium chloride - it's non-reusable. You can get buckets of reusable desiccants like silica gel on industrial supply sites like McMaster Carr or Amazon.

  • My problem with a USB fan is that I can't help but turn it into a stir plate.. Commented Jul 12, 2013 at 5:23
  • Yea, that's why I have two, one for the fridge and one for starters :)
    – paul
    Commented Jul 12, 2013 at 16:34

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.