Fridge/Fermenter Temperature

[mreed]

In putting your fermenter in a fridge and controlling its temperature using an external controller.
I have seen the Thermowell that is inserted in to the carboy and the temperature is read from inside the carboy.
My question is that if I use an external controller to control the fridge’s compressor.
Isn’t the compressor going to be running longer then needed due to the amount of liquid in the carboy, isn’t there going to be large temp swings in the fridge?
Wouldn’t it be better to keep the ambient air temp in the fridge the constant and let the liquid temp follow the ambient air temp?

Thanks
Mark

 

[NTXBrauer]

I have not heard of anyone placing the controller probe inside the carboy. Most either adhere it to the outside of the carboy, or let it free float in the fermentation chamber.

If attached to the carboy (or inside) the probe is reading the temp of the liquid which will require the compressor to run for a longer period of time to lower the temp of liquid vs lowering the ambient air temp.

The liquid is more stable than air and will hold its temperature longer, which will result in the compressor being turned off for longer periods of time as well.

If your probe is measuring the ambient air temp, then you can expect the compressor to run for a shorter period of time, but cycle on/off more frequently to maintain a consistent temp. This excess cycling can cause more damage and shorten the useful life of the compressor IMO.

I have done both, but prefer to adhere the probe to the carboy.

 

[LLBeanJ]

I use a thermowell and probe the center mass of the beer/wort.

Most temp controllers have a delay setting to prevent short-cycling. Mine is set to require at least 15 minutes between each compressor cycle.

I also have a 1°F setpoint differential, so that the heat/cool cycle starts when the probe temp exceeds ±1° from the setpoint. This prevents wild swings in the liquid temp.

 

[Jorb]

The liquid is more stable than air and will hold its temperature longer, which will result in the compressor being turned off for longer periods of time as well.

If your probe is measuring the ambient air temp, then you can expect the compressor to run for a shorter period of time, but cycle on/off more frequently to maintain a consistent temp. This excess cycling can cause more damage and shorten the useful life of the compressor IMO.

I have done both, but prefer to adhere the probe to the carboy.

I agree. I strap the probe next to the carboy.

 

[NTXBrauer]

I just looked into the carboy thermowell. If you get one of these, I would use it vs. free floating the probe. It will save the excess compressor cycling. Cheers!

 

[LordUlrich]

The thermal mass of the air is really low compared to your wort. Which means it will change temperature far quicker but it may not mean that the wort will ever reach that set temperature (it may not follow the temperature like you think). Keep in mind that fermenting beer is a heat source.
Also when it comes down to it you care about the temperature of the beer not the air.

Sent from my DROID RAZR HD using Home Brew mobile app

 

[raouliii]

...Wouldn’t it be better to keep the ambient air temp in the fridge the constant and let the liquid temp follow the ambient air temp?....

IMHO, no.

The temperature of the wort/beer is what we are trying to control for the best fermentation results. Monitor and control the wort/beer with an insulated probe on the exterior of the bucket or carboy, or a thermowell. I do the first option and it works great.

The liquid temperature will not always closely track the ambient air temperature, especially during the early, active, exothermic stages. These early stages of fermentation are the most critical for temperature control and quality of the finished beer.

 

[mreed]

My main concern/thought is that if the thermowell in the wort is telling the controller to turn on the compressor to cool, let’s say 1 degree. The compressor turns on and starts cooling, and it runs until the temperature drop is pushed all the way through the wort to the center where the thermowell is. That the temp in the fridge (or chest freezer) is going to be so cold that the wort in the outside of the fermenter temp would continue to drop well below the desired temperature.

 

[LLBeanJ]

No matter where you measure the wort temperature, you're going to be dealing with inaccuracies due to the thermal dynamics of the situation. Probe the center of the wort with a thermowell, and the outer area will be colder/warmer, as you described. Conversely, probe the outside of the vessel and the inner mass will be colder/warmer. With the simple setup that we're dealing with in using a chest freezer or equivalent, there's just no getting around it. The good news, however, is that it works leaps and bounds better than just controlling ambient temp, or not controlling it at all, for that matter.

Bottom line is: Do whichever method works better for you. I decided on the thermowell because I wasn't interested in dealing with attaching and insulating a probe to the side of the vessel. I found it much easier to drop in the thermowell through the air lock port and slide the probe down to the bottom. Finished. No tape, or bubble wrap, or foam, or whatever... YMMV

 

[petrolSpice]

I have noticed that during active fermentation, there is a churning motion that is going on inside the fermenter, it is easily visible though a glass carboy. I would think that this motion can relatively quickly transfer cold/warm fluid from the outside of the carboy to the center where the probe might be.

If you measure the temp of the center, then the outside might get too cold/warm. If you measure the temp of the outside, then the center might be too warm/cold. Pick your poison. Or you can get another temp probe and wire them so it takes an average of the center and outisde.

 

[BigFloyd]

It's pretty simple. Tape the sensor to the side of the fermenter bucket/carboy and cover it with bubble wrap or something similar to insulate it from the air.

Some folks here on HBT have already done experiments where they read the temps simultaneously with one sensor taped to the side and another in a thermowell in the middle of the liquid The peak difference was an insignificant 1*F.

You shouldn't have temp swing issues if you follow the practice (which you should anyway) of chilling the wort a few degrees below the initial target ferment temp. Even if you don't, given a little time any swings will subside.

 

[petrolSpice]

I tried it out today...

Probe taped to side of carboy with a folded up long sock for insulation = 17.9C
Probe dipped directly into center of wort = 17.7C
Ambient temp in room = 21.1C

I run my probe through the blow off tube and let it sit directly in the wort since it's waterproof.

 

[mreed]

Thanks for all the great information. I think I will use the thermowell through the rubber stopper.