Question - Controlling Temp During Active Fermentation

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NateDawg

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Hi all,

I'm planning to start controlling the temperature of my beer fermentation with a chest freezer and temperature controller, which has led to a few questions.

I read that active fermentation can cause beer temperatures to increase to 5+ degrees warmer than ambient temps, but I've noticed that may people allow their temperature probes to dangle freely in their freezers/fridges, while others tape them to the side of the fermenter then cover the probe with insulation. I'm assuming it could take a while for a single 5 gallon fermenter to heat up the ambient temperature of a 7 cubic ft freezer, so, would it be a better practice to always tape and insulate the probe? What if I have 2 fermenters in the freezers, both of which have different internal temps? Would you just place the probe anywhere in the freezer and set the the controller temp a few degrees lower than the target temp to offset the increase in temp?

Maybe I'm overthinking all of this an simply placing the probe anywhere in the freezer then setting the controller to target temp is sufficient?

Thanks,
Nate
 
The idea behind temp control is to maintain the beer at a constant temp, not to control the ambient temp inside the ferm chamber. To do this, one should attach the temp controller probe directly to the fermenter, either by placing it on the outside, under some insulation, or in the beer by means of a thermowell.

With regard to 2 different batches at once-you can’t. It’s not possible to maintain two different fermenters at different temps with one temp-controlled ferm chamber. I have started a new batch when the previous one was at 70° but only for 12-24 hours. That gets the yeast started a bit quicker in the newest batch, then the previous batch is removed for packaging and the temp dialed back to the desired range for the remaining batch.
 
+1 on what grampa said.

I think 5 gallons of 1.05 OG beer produces somewhere between 5 to 10W of heat for three days. Maybe 10W on the first day, and then 5W for the next two days. So you could try insulating the batch you want to run hotter a little bit, or put it in a more spherical container than the colder batch. There's a bit of math involved, but you could always do a trial run if you don't want to risk real beer (1.05 OG is about 6 pounds of sugar in 5 gallons of water, and baker's yeast should do).
 
I like that test run idea - might try that out once I get temp logging set up. I plan to use a thermowell sensor in addition to one taped to my heater - the idea is to write a PID algorithm that uses the taped heater for the PI terms and the thermowell for the integral term. That ought to maintain good loop dynamics but eliminate the temp delta between heater and wort...
 
+1 on what grampamark said.

In general, it's a bad idea to have the probe of a temp controller dangling in the air of a chamber. You want it to be in a thermowell inside the fermenter, or taped to the side of the fermenter (under insulation), or inside a separate container of liquid. In the bottom of my keezer I have a bottle of water with a thermowell that holds the temp probe. In my fermentation mini fridge I use a thermowell inside the fermenter.

Regarding fermenting multiple beers at once, it's not uncommon to see folks who have two or more mini fridges set up for fermentation. That way each can have its own separate temperature conditions. The same thing can be done with setups that pump chilled glycol from a central reservoir. Each fermenter has a separate temp controller and glycol pump.

On the other end of the spectrum, I've seen photos of brewing club walk-in fermentation chambers where the temp of the room is controlled by a wall mounted air conditioner. Variations in temp can be accomplished by moving a fermenter from the floor to a higher shelf.
 
The internal temp of the beer is what you want to control. But, if you run a standard controller off of that internal measurement (probe in a thermowell) you will get big temp swings.

I've made plenty of decent beer doing it that way, but I've since gone to controlling via a probe that is taped/insulated on the outside. I've kept the internal measurement also just for informational purposes. I've found that the internal temp stays bang on within one degree of the set temp at all times this way. The external probe will of course read lower immediately after a cooling cycle, but internal is very stable.
 
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