Chest Freezer Fermentation Chamber High/Low Temps

[BroccoliMangoAle]

Okay this is the first time I couldn't google a homebrewing question.

I got a chest freezer and a hot/cold power controller with a no-light heat lamp for heat and I'm trying to run some tests to see how it does keeping a fermenter full of liquid at 67 degrees. It seems to work pretty well mostly. I've got two waterproof sensors hanging in the water, one for the controller and the other for a Raspberry Pi that's graphing the temps on a web server I can hit on my home network to keep an eye on it. The temps are staying nice and tight since I started using water to test instead of just hanging the probes in the air inside the freezer.

The problem is that the water in the bottom of the fermenter is like 25 degrees cooler than the water at the top, regardless of where the probes are. So if the probes are in the bottom, the temps at the bottom stay right near 67, but the top is in the 90's.

I imagine with yeast activity swirling around in a wort the temps will be a little more uniform, but how do I get a uniform temperature throughout the fermenter after active fermentation is over? Big-ass stir plate?

All I can think to try is put some kind of insulation under the fermenter so it isn't sitting right on the freezer bottom, and making sure the heat lamp isn't pointing directly at the fermenter itself.

 

[Morrey]

You are pretty well on target by saying that yeast activity during fermentation will keep things stirred up in the fermenter for the most part. 67F - 90F is a real wide spread so that may need reviewing. I put my fermenters on a rubber door mat just to keep them off the freezer floor, but my freezer has coils running around the sides too so I didn't see that much difference in mine.

Some folks use a small fan, I know I did when I used an Inkbird controlling a freezer and reptile heater element. The AC computer server fan I used blew air across the heating element to circulate air evenly. The cooling aspect of the freezer should not require much circulation, so I hooked my fan to run along with the heat element.

I found the best place to run a probe was to drill holes and place thermowells in the fermenters. An alt place is to tape the probe to the fermenter and cover the probe with insulation....or submerge the probe in a separate vessel of water like you are currently doing. Using a probe in "ambient" is the least valued choice and is highly inaccurate.

Sounds like you are thinking clearly and heading in a good direction.

 

[BroccoliMangoAle]

I will probably try a fan if my little tweaks don't help.

Any thoughts on waterproof sensors directly in the beer? Other than careful sanitization of course.

 

[FunkedOut]

A sheet of plywood between the fermenters and the freezer floor should fix your temp gradient.

 

[Morrey]

I will probably try a fan if my little tweaks don't help.

Any thoughts on waterproof sensors directly in the beer? Other than careful sanitization of course.

If the probe is waterproof, all should be fine. BUT...how will you get the probe under a lid or in the beer and maintain an airtight lid? Or are you doing an open fermenter?

 

[BroccoliMangoAle]

If the probe is waterproof, all should be fine. BUT...how will you get the probe under a lid or in the beer and maintain an airtight lid? Or are you doing an open fermenter?

Haha good point. I'm sure it would have occurred to me between now and brew day.

 

[BroccoliMangoAle]

A sheet of plywood between the fermenters and the freezer floor should fix your temp gradient.

I'm trying a couple of my extra floor boards that happen to fit down there.

 

[Morrey]

If you tape the probe to the side of the bucket, then tape a neoprene beer hugger over the probe to insulate against ambient air, all should be fine. That's a very common way to do this.

 

[pigroaster]

I tape mine to a suspended freezer pack with insulation aluminum foam between the probe and the tape for my keezer. Works great!

 

[day_trippr]

A sheet of plywood between the fermenters and the freezer floor should fix your temp gradient.

Highly doubtful as the evaporator loop on a chest freezer starts a few inches below the lid and ends a foot or more above the floor. The floor is essentially inert.

What actually does fix stratification is a small DC fan - I use a single 120mm 12V ball bearing fan spinning on a 9V supply and it totally evens the temperature from just under the lid to just above the floor (the green and yellow channels). This happens to be a keezer, obvious, but the physics are the same.

fwiw, the purple "Keg" channel probe is strapped to the side of one of six kegs near the bottom with a pad of 1" thick closed cell foam covering it. In this plot the compressor is cycling on a 4:45 period for about 45 minutes ON time per cycle, with a 35°F Set Point and +/-1°F differential. As one can see it is fairly flat through the full cycle, meaning the probe is well isolated from ambient...

Cheers!

 

[BroccoliMangoAle]

I checked it again today after letting it sit on boards for the night and it looks like the temp difference from water at the bottom of the carboy to the top is only about 5 degrees now instead of close to 30.

I am also going to steal a fan from work, but my probes are currently completely isolated from ambient. Anyway, thanks for all of the replies, this is good stuff.

 

[LittleRiver]

A thermowell from BrewersHardware works well for me. I like having the temp probe right in the wort. Well worth the few bucks it costs.

 

[troglodytes]

I was super stoked to get my thermowell installed only to find out it did a much poorer job at a non-raspberry pi setup at miimizing temp swings. When I had my thermometer in the thermowell, the heating element or cooling was running long enough before the thermometer adjusted down to that the heated (or cooled) air continued to raise (or drop) temps for well after it shut off resulting in temps swings of about 3F and the compressor kicking on more often to compensate.

I have since attached the thermometer to the side of my fermenter and simply covered with either insulation or a sponge (all just bungie corded on tight) and my temp swings only over/under shoot by about 1-1.5F and the compressor kicks on less. Let me tell you this has done wonders for my saisons and belgian strains that love to quite when temp drops occurred.

If you have an intuitive raspberry pi setup that can predict over/undershoot and really level out the temp swings, then you should be fine, and the thermowell solution is probably best. But if not I highly suggest that cheap and easy method I've employed.

 

[day_trippr]

You are not the first to report this control behavior when using a thermowell in a large fermentor. It seems there must not be enough induced movement to keep the full volume thermally homogenous to a functionally acceptable degree, thus the reading at the center has a fairly large lag vs the temperature towards the perimeter.
Seems strange but I haven't read of a reasonable alternative explanation...

Cheers!

 

[FunkedOut]

The temp of the liquid in the center of the fermenter takes a while to reach the desired temp.
By the time that happens, the air in the fermentation chamber is so cold that it continues to chill the fermenter and the liquid inside it, long after the compressor has turned off. This causes the undershoot.

You can limit this behavior by powering the controller using the thermowell temp with a controller using the fermentation chamber air temp.
Set the desired air temp to ~5*F less than desired thermowell temp.
This setup reduces undershoot almost completely.
I get 0.3*F undershoot with a delta of 3*F.
Biggest benefit of using a thermowell is knowing exactly what the wort temp is and not having to guess at heat generated by various phases of fermentation.

 

[day_trippr]

Ok, I read that twice and it still seems like a lot of squirming about.
How does "using the thermowell temp with a controller using the fermentation chamber air temp" justify even having a thermowell'd probe to begin with?

Cheers!

 

[FunkedOut]

You need to start your quote a few words earlier.
It’s about feeding power to “the controller using the thermowell temp with a controller using the fermentation chamber air temp.”

 

[troglodytes]

So does this mean you have two temp probs and two temp displays? One to measure what the actual wort temp is at the center of the fermenter and one to run the heat/cooling switch based on the chamber air temp?

 

[FunkedOut]

Yes, two controllers, each with their own probe.

Plug the freezer into the controller with its probe in the thermowell.
Plug that controller into the controller with its probe in the freezer air.

When the freezer air temp reaches 5*F below the desired wort temp (or whatever setting you choose), the controller will kill power to the controller that has its probe in the thermowell. Freezer will not be powered up.

Freezer air temp never drops low enough while the wort catches up to cause undershoot.

You can actually switch the order of controllers and it works the same.
Freezer > Air > Thermowell
This way, you can plug a heater into the thermowell controller.

 

[BroccoliMangoAle]

A controller within a controller?

 

[Morrey]

I use a short extension cord to plug my heater and circulation fan into together so when the heater powers up, the fan comes on too off the same power plug. Of course the freezer is plugged into the cooling plug on the Inkbird while the heater and fan are plugged into the heat plug. I want one controller to do this process so there is communication on both sides of the heat and cool cycles.

There are swing (hysteresis) settings and compressor delay settings available on my Inkbird to keep cycling to a minimum. Many ATC devices can be setup with custom settings like this.

 

[FunkedOut]

I’m using inkbirds myself.
Using the “Freezer > Air > Thermowell>” configuration,
set the hysteresis and compressor protection values on the thermowell controller. Plug the heater/fan there too.

Set hysteresis and protection values to minimum on the air controller.
All this one does is limit how much colder than target temp the air reaches.

I only use a heater when ambient temps are cooler than desired fermentation temps. That’s a rare day in FL.
The rest of the year, the heater never kicks on.

 

[yeastieboysbrewing]

I've always used my inkbird in the strapped to the side with insulation setup, but am considering going with the Freezer>air>thermowell option (so I can always read the current thermowell temp) after seeing this thread. If I put a small fan inside to circulate the air also (powered on constantly), will that cause too much swinging in the air temp and therefore turn the compressor on/off too much with the compressor protection turned off on that controller?

 

[FunkedOut]

I’m now running a fan inside the chest freezer constantly.
After adding a collar and moving the air temp probe up to the collar, I ended up freezing about 15 gallons of beer that shot up and out of the safety pressure release valve.
Lessons learned. There was about a 20*F difference between top and bottom of freezer.
Now with the fan, there’s less than 1*F.

I’ve also moved to freezer > air > thermowell > power so I can always read the beer temp.

The fan doesn’t induce swinging. That’s dictated by thermal mass, insulation and temperature differences between inside and outside of chamber.

 

[yeastieboysbrewing]

I’m now running a fan inside the chest freezer constantly.
After adding a collar and moving the air temp probe up to the collar, I ended up freezing about 15 gallons of beer that shot up and out of the safety pressure release valve.
Lessons learned. There was about a 20*F difference between top and bottom of freezer.
Now with the fan, there’s less than 1*F.

I’ve also moved to freezer > air > thermowell > power so I can always read the beer temp.

The fan doesn’t induce swinging. That’s dictated by thermal mass, insulation and temperature differences between inside and outside of chamber.

Thanks! And while I understand this method will solve the cooling overshoot, do you find that it is still able to keep the active fermentation from warming too much with only a ~5 degree differential of air vs target wort temp?

 

[FunkedOut]

The 5 degree differential doesn't present a problem with temp overshoot at all.
In fact, depending on the ambient temperature, it can lead to undershoot problems. The wort can get as much at 2*F colder than set temp.

I've since settled on 3 degrees cooler air than the desired wort temp.
With 8 minutes delay protecting the freezer from cycling too often, I get +1*F / -0.5*F regardless of summer or winter (Florida).

I use a 60Watt light bulb connected to the thermowell controller in the winter.

 

[yeastieboysbrewing]

The 5 degree differential doesn't present a problem with temp overshoot at all.
In fact, depending on the ambient temperature, it can lead to undershoot problems. The wort can get as much at 2*F colder than set temp.

I've since settled on 3 degrees cooler air than the desired wort temp.
With 8 minutes delay protecting the freezer from cycling too often, I get +1*F / -0.5*F regardless of summer or winter (Florida).

I use a 60Watt light bulb connected to the thermowell controller in the winter.

Thanks for all the insights. I use a 60 watt bulb also for heating in the winter. Sounds like I need to get me a second inkbird and make this happen.

 

[odie]

I just drop the probe in a large jug of water. As long as you don’t get into the freezer all the time I would think the temperatures would be fairly uniform