Tape temp controller to carboy and insulate - Really???

[kombat]

Like many, I have a chest freezer I'm using for fermentation, connected to a temperature controller with a temperature probe. I have the probe just dangling in the air inside the freezer.

However, I've read in multiple places that ideally, the temperature probe should be taped to the side of the carboy, and covered with insulation, so that it detects the temperature of the wort, and not the air in the freezer.

Wouldn't this cause wild swings in temperatures inside the freezer?

I mean, it seems to me that once the temperature of the wort rose to the "threshold" that caused the controller to turn on the freezer, the temperature controller would run the freezer until the temperature of the probe gets back below the threshold. However, since the probe is attached to the carboy, and insulated from the rest of the freezer, this will take a very long time, won't it? The freezer will run until the beer finally drops to the desired temperature, and since it's a large volume of liquid, that will be a while, right? By the time it finally drops low enough, wouldn't the ambient temperature in the freezer be well below freezing? And then, as the hours pass, the freezer would warm up, but the beer (again, due to having a large thermal mass) will change temperature more slowly. By the time the beer finally warms up to a degree or two above threshold, won't the temperature of the rest of the freezer be practically equal to the room temperature?

I guess I just don't understand why such a configuration is preferable to just keeping the temperature inside the freezer at precisely 45° F (or whatever). It seems taping the probe to the carboy and insulating it would cause wild temperature swings, and a "full-throttle/hibernate" demand on the freezer's compressor. What am I missing?

 

[Felixio]

The configuration is designed such that the beer is at a stable temp through fermentation. Sure, the surrounding air may go through fluctuations, but you're not trying to ferment the air inside your freezer. You're trying to ferment the beer.

On the other hand, if you know that your desired range is (for example) 60-65, and you know that with your system, if the fridge is 60, then your beer will be 62 or 63 (a good reason to have a second probe). Knowing this, we can place the probe in a 22oz bottle of water or hanging in the middle of the fridge and set the controller to 60, knowing that the beer will stay in the middle of the desired range.

Of course, this is all coming from a guy that is planning his fermentation chamber and saving money for the fridge (we just happen to be planning a kitchen remodel, too, hehehe) so I still yield to everyone with hands-on experience.

 

[AnOldUR]

I guess I just don't understand . . . It seems taping the probe to the carboy and insulating it would cause wild temperature swings . . . What am I missing?

I agree. If you're using a freezer with a temperature control, the ambient temperature will reach below zero when the control is calling for cooling. With the probe on the carboy or in a thermowell, you'll get a yo-yo effect in your wort that slowly decreases until stabilizing at the temperature set on your controller. If you use a refrigerator and set the units temperature high enough (but control the on/off with a temperature control) these effects will be minimal because of the mass of the wort.

I measure both wort and ambient temperature, but have the controller probe in the ambient air. During active fermentation I set the controller to whatever ambient temperature is needed to keep the wort at the proper temperature. That can be anywhere from 5 to 10 degrees colder than the wort. As fermentation slows, I make manual adjustment to the ambient temperature until the two stabilize. This method is more labor intense, but it does prevent any swings in wort temperature.

 

[pabloj13]

I think, even with the insulation, my probe reads a combination of ambient and wort temp. This really dampens the yo-yo effect. The temp sticker on the side of the carboy reads pretty darned constant, within a degree or so. Obviously the center of the wort may be a little bit different, but I'm not too worried about it.

 

[chuckstout]

If the temp in the freezer is 68, then you chill the wort to 66 and strap your prob and then insulate it. The temp controller would believe it would need to be off. Your ale would then free rise to the desired 68 and you would know it will hold that temp +/- 1-2F. Where if your temp probe is dangling controlling the ambient temp you would have much greater swings in temp because of the active yeast. My biggest concern would be If I coundnt moniter the yeast temp and towards the end of fermentation the yeast staled out because a huge flux in temp

 

[BigFloyd]

Like many, I have a chest freezer I'm using for fermentation, connected to a temperature controller with a temperature probe. I have the probe just dangling in the air inside the freezer.

However, I've read in multiple places that ideally, the temperature probe should be taped to the side of the carboy, and covered with insulation, so that it detects the temperature of the wort, and not the air in the freezer.

Wouldn't this cause wild swings in temperatures inside the freezer?

First of all, I don't care what the air temp in my fermenter chamber is. Only the fermenting beer temp matters. The best way I can do that, absent a thermowell into the vessel, is to tape/insulate the probe on the side of the bucket. I find that it works quite well.

Yes, my fridge has to sometimes get colder than the liquid in the bucket/carboy in order to cool it down and keep it cool. That's especially true during active exothermic fermentation. As I watch the temp readings on the STC-1000 (I use three of them for different brew-related appliances), they fluctuate very slowly due to the thermal mass of the 5 gallons of liquid being monitored.

Monitor the air inside the freezer if you want, but you're not getting an accurate read on your fermentation temps by doing so.

 

[GotPushrods]

+1 to what everyone else has said.

If you keep your chest freezer at a constant, say, 65... your beer will quickly rise to 70+ during the first few days, then back down.

Also, when you dangle the probe in the air, the compressor will cycle on/off a LOT more than if it's taped to something with a little mass. It's not running hours that age a compressor. It's on-off cycles.

If you want your freezer to last more than 5 years (especially one of these newer "Energy Star" appliances where the engineers get 2nd dibs at design), I highly suggest you tape that probe to SOMETHING.

 

[AnOldUR]

Monitor the air inside the freezer if you want, but you're not getting an accurate read on your fermentation temps by doing so.

The object is to monitor both the wort temperature and the ambient, but to adjust the wort temperature by setting the ambient to a temperature that compensates for the heat produced by fermentation. It takes a little more work making the adjustments daily, but your wort stays at a more constant temperature.

You talk about the wort having thermal mass. Well, so does the air and surrounding walls in the freezer. With the controller responding to wort temperature the inside of the freezer will go to subzero before the controller turns off. After that your wort temperature will keep dropping until the two balance out. This cycle of rise and falling wort temperature keeps repeating itself throughout active fermentation.

Adjusting the ambient with a 5 degree differential setting on your controller will not cycle your compressor too much, but with a little effort will result in more stable wort temperature. Stability is almost as important to yeast health as the actual temperature.

 

[Shooter]

I'm not sure the wort drops much more than a degree or so past your set point though. I used to set my refrigerator to come on at +1 above the setpoint and a heating pad to come on at -1 below the setpoint. That didn't work. The chiller would turn off and then 15 minutes later the heater would start kicking on. The two were in a constant battle. Dropping the heater to only activate at -2 below the setpoint, solved that issue. The heater never really comes on at all now. Now, in this scenario, I'm using a small dorm style fridge which probably isn't as well insulated as some people's setups, but I don't think the numbers in the wort fluctuate drastically.

 

[jbaysurfer]

I'm no physicist, but the thermal inertia of the surrounding air is virtually nil compared to the thermal inertia of the wort/beer. Therefore, freezing air in the fridge/chest freezer is not going to cause a giant yo-yo effect, because it doesn't have enough inertia to rapidly move the wort temperature down to a point where it would be problematic. By the time equilibrium is reached the wort might be 1-2 degrees on the cool side, but active fermentation will quickly close this gap with it's own heat generation.

Ultimately the ONLY time I ever have the chest freezer ambient temp in the freezing range is upon initially cooling the wort (assuming my IC didn't get it all the way there). But that's ok with me. Yeast tend to like a cool start then a warm up to recommended temps anyway.

Lastly, I will say that if you have a 2-way temp controller that triggers a heat source as well, you WILL see the heat/cool cycles fighting each other in the early going. To alleviate this, just set the heat cycle to kick in at a lower temp, or increase the buffer on it so it's not so quick to kick in. Again, in the early going if your wort temp drops to 63 rather then 65 on your ales, it's not a bad thing.

My example:

I typically set my dual temp controller to 63 on the cooling phase at the beginning of an ale fermentation with a buffer of 2 degrees. I will set the heat to 62 with a buffer of 1 degree. When the wort temp suffers that first drop in temp down to 61, the heat kicks in and adds 1 degree then shuts off. The wort will free rise from 62-64 and at 65 the cool cycle kicks on again. This time the wort will likely NOT drop down to 61 (each successive "yo-yo" gets smaller due to newtons 1st law). At high Krausen I increase the heat setting to 63 instead of 62, and a day later I set them both at 64.

I could go on, but I've already been to verbose. Disclaimer: I took physics for social science majors in college. All the above is truly born of experience running a dual stage temp controller in a chest freezer since my very first fermentation.

 

[el_caro]

First of all, I don't care what the air temp in my fermenter chamber is. Only the fermenting beer temp matters. The best way I can do that, absent a thermowell into the vessel, is to tape/insulate the probe on the side of the bucket. I find that it works quite well.

Yes, my fridge has to sometimes get colder than the liquid in the bucket/carboy in order to cool it down and keep it cool. That's especially true during active exothermic fermentation. As I watch the temp readings on the STC-1000 (I use three of them for different brew-related appliances), they fluctuate very slowly due to the thermal mass of the 5 gallons of liquid being monitored.

Monitor the air inside the freezer if you want, but you're not getting an accurate read on your fermentation temps by doing so.

+1
Same method here

 

[BigFloyd]

You talk about the wort having thermal mass. Well, so does the air and surrounding walls in the freezer. With the controller responding to wort temperature the inside of the freezer will go to subzero before the controller turns off. After that your wort temperature will keep dropping until the two balance out. This cycle of rise and falling wort temperature keeps repeating itself throughout active fermentation.

I'm sorry, but this is a specious argument.

There's no apples-to-apples comparison between the thermal mass of 5 gallons of wort and the thermal mass of the air inside a freezer/fridge. A cubic foot of water weighs in at 62.2 lbs (at 65*F) whereas the same volume of air weighs in at a whopping 0.0807 lbs - a 770:1 ratio.

So, assuming that the freezer airspace is 10 times the volume of the wort, the thermal mass of the wort is still about 77 times that of the air inside the freezer. Even if the air temp is 30*F below the wort temp when the unit shuts off, the wort temp will only drop another degree or so before the two balance out (or not drop at all if it's in the exothermic phase). My observations of the temp readout (w/ sensor taped on the fermenter) at the conclusion of the cooling cycles over several batches confirms this to be the case.

 

[CryoEng]

I'm sorry, but this is a specious argument.

There's no apples-to-apples comparison between the thermal mass of 5 gallons of wort and the thermal mass of the air inside a freezer/fridge. A cubic foot of water weighs in at 62.2 lbs (at 65*F) whereas the same volume of air weighs in at a whopping 0.0807 lbs - a 770:1 ratio.

So, assuming that the freezer airspace is 10 times the volume of the wort, the thermal mass of the wort is still about 77 times that of the air inside the freezer. Even if the air temp is 30*F below the wort temp when the unit shuts off, the wort temp will only drop another degree or so before the two balance out (or not drop at all if it's in the exothermic phase). My observations of the temp readout (w/ sensor taped on the fermenter) at the conclusion of the cooling cycles over several batches confirms this to be the case.

"Thermal mass" requires including the specific heat (heat capacity) of the material as well, not just "mass," but this is the correct thought process. You'll also need diffusivity, conductivity and the solution of a reasonably complex differential equation to model the system. Also, remember, the beer is chemically producing heat. Your fridge system should balance that energy fairly well and produce a nice constant temp. 5 gallons of water is a pretty good thermal dampener (large thermal mass).

I've never really understood why people use heat and "cold" sources. Generally, your either fighting the heat generation of the beer and the sun or the cold arctic wind. One source should be enough to oppose the heat gain (or loss) and maintain a constant temp. Alternating heat and cold sources will naturally make the system hard to tune. But again, why use both?

Insulate the system from the external world sink/source and just fight from one side. I switch on my air conditioner when it gets warm and set the thermostat. When the season changes and it gets cold, I turn on my heating system and set the thermostat. I don't run to the thermostat and switch between modes.

One thing I always like to remind folks, your system is monitoring the temperature of the sensor. Nothing else. It's up to the system designer to get the sensor temperature to be representative of the sample temperature.

Taping the sensor to the outside of a glass bottle is thermally closer to the material of interest, but there is still a fair bit of conduction in the sensor lead, through the insulation applied, etc, etc.

If the sensor is representing the temp of 5 gallons of water (beer), you're really going to have to work to get it to "yo-yo" (oscillate or ring). If it's only representing itself (a few ounces of metal) and you're hitting it with alternating heat and cold sources, yeah, you'll never get it damped out. Once again, why use two sources?

Oh, actually, I am a thermal physicist...

Cheers!

 

[devils4ever]

I need to heat and cool since my setup is in the garage. Morning temps are in the 30s and evening temps in 60s.

Right now I'm using a 15 W light bulb for heat, but it's not connected to a temp controller. I need to add one. But, what should I use for a better heat source?

 

[BigFloyd]

I need to heat and cool since my setup is in the garage. Morning temps are in the 30s and evening temps in 60s.

Right now I'm using a 15 W light bulb for heat, but it's not connected to a temp controller. I need to add one. But, what should I use for a better heat source?

Your situation is similar to when I was doing my fermenting in the garage in a chest freezer in winter. I used an STC-1000, which is an automatic dual temp controller, with a 2-outlet household receptacle wired into it. My chest freezer (plugged into the "cool" outlet) activated only when the temp rose 0.5*C (roughly 1*F) above my target temp and turned off when the target was reached. The times when it was cold in my garage, the freezer remained idle unless the ferment was very active and producing lots of its own heat.

I had one of these - http://brewstands.com/fermentation-heater.html plugged into the "heat" outlet and placed inside the freezer. It generates heat, but no light hits your fermenting beer. It only powered up when the temp dropped 0.5*C below the target temp. When it warmed back up to the target, it turned off.

The way that setup worked, I never had the heat/cold sources fighting against each other. Either one was on and the other off, but never both and often neither. You can also adjust the tolerance (0.5*C is default). I now have mine set at 0.7*C on the fermenter fridge in my basement and it works very well.

 

[Shooter]

Once again, why use two sources?

A lot of people just have two stages setup so they can be ready for any eventuality. The key is to have the cycle on the source your not using set wide enough that the two aren't competing. I'm using the refrigerator 95% of the time, but the heating pad is always hooked up, no reason to unplug it everytime. I only use the heat source on rare occasions. For example, on the saison I've currently got going I started at 68 degrees and, once fermentation started going for a day or so, I started slowly ramping the temperature up over the next four days.

 

[jbaysurfer]

Cryo, I have a heat source because I like to ratchet up the temp for diacetyl rests at the end of my primaries. As I described above, It probably only kicks on once prior to that, when the initial cooling phase drops it below 61 (for ales, just as an example). I use a 40W bulb and I keep the fermenters safely covered from the light....in fact, I'm probably a little overkill on that front, but I like hoppy beers ;-)

I loved your post. Check out the brain on you!

 

[devils4ever]

Well, right now I'm using a clamp light with aluminum reflector pointing down to hold the bulb. The light is not reaching the carboy. The heat is radiating through the aluminum reflector and is not very hot with the 15 W bulb. But, I'm looking for a better solution. The paint can with 60 W bulb seems interesting.

 

[BigFloyd]

The paint can/ light bulb heater works well. Be mindful when building it to well-insulate all wires and connections from the metal of the can lid.

You can vary the wattage of the bulb depending on your heating needs.

 

[jbaysurfer]

Well, right now I'm using a clamp light with aluminum reflector pointing down to hold the bulb. The light is not reaching the carboy. The heat is radiating through the aluminum reflector and is not very hot with the 15 W bulb. But, I'm looking for a better solution. The paint can with 60 W bulb seems interesting.

I don't know how big your chest freezer is, but a 40 watt bulb is plenty of heat for my purposes. (I have a 7CuFt chest freezer that fits two carboys in the well, and I put my stir plate and a blowoff jar on the compressor hump).

 

[devils4ever]

I don't know how big your chest freezer is, but a 40 watt bulb is plenty of heat for my purposes. (I have a 7CuFt chest freezer that fits two carboys in the well, and I put my stir plate and a blowoff jar on the compressor hump).

My chest freezer is holding my kegs. My upright refrigerator (about 14-15 cu ft) is holding my carboy. The 15 W seems to be barely enough when the temps drop. But, since it's not connected to a temp controller, it's better than the fridge running a lot. I need to add a Johnson controller and a larger heat source.

 

[BigFloyd]

I need to add a Johnson controller and a larger heat source.

Better yet, snag an STC-1000 off of Amazon for $20, build a little 2-outlet controller box and handle your sometimes-cold garage that way. I've not had any problems at all out of the three that I use.

 

[FatsSchindee]

The paint can/ light bulb heater works well. Be mindful when building it to well-insulate all wires and connections from the metal of the can lid.

You can vary the wattage of the bulb depending on your heating needs.

Since you've had good success with the paint can heater, I have a question for you (or anyone else that's using one):
Did you have any issue running the cord from the heater into (or out of, depending how you look at it, I guess) the chest freezer? I've read that the temp probe is no issue just running over the edge of the freezer and beneath the seal of the lid because it it so thin/small. But how about the cord for the heater? I didn't use the flat two-wire cord - I used the thicker round three-wire one because I wanted it grounded, but am wondering if it will be too thick and break the seal enough to make the freezer that much (I would doubt TOO much) more inefficient. Was thinking about drilling a hole in the lid (or side of lid - but not the side of freezer) to run the wire through, but not sure how to plug or caulk it up to keep from too much temp control loss...

Thanks for any help!

(I built the heater already, bought a 7.2 cu ft freezer off Craigslist ($60!), and have the correct (initially was sent the wrong 220v) 110v STC coming on Monday... Now I'm just trying to iron out details!)

 

[BigFloyd]

Me, I'd switch to a flat cord and close the door over it.

 

[FatsSchindee]

Me, I'd switch to a flat cord and close the door over it.

That probably would be easiest... Even without rewiring the can, just try to find a flat grounded cord (I may have one lying around somewhere) and splice it into the round cord at a short distance from the can, so the flat cord will go under the lid. Thanks!

 

[devils4ever]

Yeah, I used a flat cord and haven't had any issues. I would imagine a round cord would be fine as well.

 

[thisisbeer]

I have a thermowell with a probe in my wort and connected to a digital thermometer. My probe for my temp controller is taped to the side of the carboy. I also have another probe hanging for ambient temp. I did this to answer this same question for my self

Now there has been no swing in fermentation temps. With 5 gallons of wort i have noticed it takes way longer than you would think to change the tempature of that much liquid. My freezer cooled 15 degrees, ambient temp, below where I was aiming when I put my carboy in the freezer. This led to a 1.5 degree temp change in the wort before the freezer warmed back up to optimal temp.

My ambient temp may fluctuate up to 10-12 degrees at times but my probe taped to the bucket only fluctuates about 1.5 degrees. The probe in the wort swings less than a degree.

I would highly recommend an extra probe and thermowell in the wort. For the simple reason the wort will be warmer than the temp of the probe taped to the side of the carboy.

Right now my freezer is 54 degrees ambient, 61 degrees on the side of the side of the carboy, and 66 inside the wort. But the wort still has very little fluctuation.

 

[zoyar]

Good info, thisisbeer. I'm planning the same setup. Can you provide some additional detail about the probe and thermowell you use in the wort (e.g., brand, source, dimensions)?

 

[thisisbeer]

I think this is the one I purchased here. Sorry it's been a while. Still works great though.

 

[Copbrew133]

That is the same setup I initially bought. Over time it had an issue with the stopper tearing a bit around the thermowell. I took the thermowell out of it and it fit perfectly into one of the inlets on a carboy cap. The other inlet holds a airlock or blowoff tube. I like the idea of monitoring the middle of the wort and haven't noticed any wild swings in temp this way.