Temperature Probe Location

I just got a Ranco ETC-111000 and a 9 cu. ft. chest freezer to do my fermentation in. My question is, where you do guys put the temperature probe? I'm thinking a glass of water, but I don't know if the probe is water proof. Then I thought I'd tape it to the side of the carboy, but the probe is pretty thick and I'd think it would pick up air temp vs. the carboy temp.

I just hang mine over my CO2 in the air. You can put it in water, however, water is less sensitive to wide temperature changes, as it takes longer for the water to equilibrate, and is therefore less accurate in measuring the freezer temp.

I tape the probe to the side of the carboy then tape 2-3 layers of bubble wrap over it to insulate.

I like this method because its the temp of the beer that matters, not the air so much.

My freezer works hard the until main fermentation is over, then the beer and the air temp equilibrate.

Beerthoven said:

I tape the probe to the side of the carboy then tape 2-3 layers of bubble wrap over it to insulate.

I like this method because its the temp of the beer that matters, not the air so much.

My freezer works hard the until main fermentation is over, then the beer and the air temp equilibrate.

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The only problem with going with the temp. of the beer is that if you have a rapid fluctuation in temperature, by the time the beer changes temp, the freezer may have already gotten too warm. Say you set it at 50 with a 5 degree differential, by the time the beer gets up to 55 degrees, the freezer might be at 60-65 degrees, compared to when the freezer gets up above 55 degrees, the beer will not be that high.

Professor Frink said:

The only problem with going with the temp. of the beer is that if you have a rapid fluctuation in temperature, by the time the beer changes temp, the freezer may have already gotten too warm. Say you set it at 50 with a 5 degree differential, by the time the beer gets up to 55 degrees, the freezer might be at 60-65 degrees, compared to when the freezer gets up above 55 degrees, the beer will not be that high.

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You are right, the air in the freezer changes temp faster than the beer, both heating up and cooling down.

The problem with going with the air temp is that fermentation produces heat, so if the air temp is, say 68º, the beer temp could be 70º or 71º, which might be too warm.

I don't care that much about the air temp inside the fridge, as long as the beer temp is where I want it to be. After main fermentation is over, the air temp and the beer temp become the same.

Beerthoven said:

You are right, the air in the freezer changes temp faster than the beer, both heating up and cooling down.

The problem with going with the air temp is that fermentation produces heat, so if the air temp is, say 68º, the beer temp could be 70º or 71º, which might be too warm.

I don't care that much about the air temp inside the fridge, as long as the beer temp is where I want it to be. After main fermentation is over, the air temp and the beer temp become the same.

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This is true. As long as there are no dramatic changes in the freezer temp, they should be equalized, and during fermentation the beer temp will always be a little bit higher.

Agreed on taping the probe to the side of the fermenter. The air temp in a fermentation chiller is irrelevent to the fermentation temp. You want the probe to be as close to the beer temp as possible.

I tried leaving the probe in the air and set it for 63F with a 3F differential, but when it reached 63F the temp would drop a few degrees more after a couple of min even though the freezer shut off at 63F. Seems like there's a lag in the temp reading?

If you have a 3f hysterieses set then it should turn off at 60 when set at 63. Also There is still quite a bit of liquid coolant in the evaporator after the compressor has been turned off. So it will still cool until the pressure in the coolant system has equalized.

Virtuous said:

If you have a 3f hysterieses set then it should turn off at 60 when set at 63. Also There is still quite a bit of liquid coolant in the evaporator after the compressor has been turned off. So it will still cool until the pressure in the coolant system has equalized.

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Makes sense. So I'm looking at 6-8F variance in air temp, should I worry? I'm trying to keep the temp around 65F while conditioning (carboy reads 66F).

I wouldnt. I just check the fermometer on my carboy and adjust the temperatur controller accordingly. My fermentor can hold 4 carboys so individual monitoring is not an option.

With a normal temperature controller, you do not want the probe to read the temperature of the wort. Most controllers do a 3F range. Suppose you want your fermentation at 65F. If your probe measures wort temperature, the unit will cycle on when your wort is 65F and will stay on until your wort gets to 62F, then shut off. Then your wort will gradually rise in temperature back to 65F and it will repeat. All you are doing is introducing a fluctuating wort temperature - the bad news. The good news is that it is fluctuating near your optimal temperature.

The flip side is hanging the probe in the air. If you set the temperature at 65F, it will cycle on at an air temp of 65F and off when the air temp gets to 62F. In the time the air temperature changes those 3 degrees, the wort temperature does not change much at all. Temperature stability is one thing you want, but there is now a disconnect between your wort temperature and air temperature (at high activity, the wort temperature can be up to 8F higher than your air temperature and at the end it equalizes). So now you have stability (good) but the stability may be around a temperature you do not want (bad).

There are two solutions. If you want a stable wort temperature, then you want a probe to measure the wort and activate the compressor to start when the wort deviates by a small amount, say 0.1 or 0.2F, not 3F. Keep in mind that the surrounding air temperature may change several degrees to effect this change, so your compressor will not be constantly cycling on and off. The second solution is to estimate the normal air temperture to wort temperature differential during fermentation and adjust your air temperature accordingly. For example, assume you know that your wort will be 5F higher than the air temperature for the first day after fermentation starts, 3F higher for the next 3 days, and 1F higher until fermentation ends. Set your temperature at 5F low on day 0, raise it 2F on day 1 after fermentation starts, then raise it 2F on day 4. In the mean time, monitor the actual wort temperature to verify that your temperature changing schedule is accurate and adjust if necessary.

I do the poor man's version on option two now. I start with the fermenter in a bucket of water 4 inches deep with a towel draped over the top and dunked in the water (max cooling). After a few days, I take off the towel so I just have the cool water at the bottom of the fermenter (some cooling). After about 5 days, I set the carboy on the cool floor (minimal cooling). I check my temperature a few times a day (more the first few days), and it has been very stable since I started doing this.

If you want precise ferment temps, an electronic controller would be best so you can set the differential to 1F, not 3. If you put the probe on the fermenter and slightly insulate it from the air, a setpoint of 68 will kick the compressor on at 69 and off at 67. Not too bad.

There are pros and cons with all the different placement options.

Bobby_M said:

If you want precise ferment temps, an electronic controller would be best so you can set the differential to 1F, not 3. If you put the probe on the fermenter and slightly insulate it from the air, a setpoint of 68 will kick the compressor on at 69 and off at 67. Not too bad.

There are pros and cons with all the different placement options.

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This is how I do it. The compressor runs longer but not as often. Do any of the commercial controllers have the ability to have finer then 1 degree F? And if they did what would the wear and tear on your compressor be?

GT

If I could do 1F, then I would probably do it this way too. I think truly you want is to limit wort fluctuation to around 0.1F to 0.2F, but with your method, you are probably getting this. The probe is mostly insulated, but not completely. The compressor kicks on and drops the air temp around, say 8 degrees, but since the probe is insulated agains the carboy, it only drops 1 degree and the wort only drops 0.1 degree and then the compressor shuts off. Perfect.

I just have the plain analog controller for my freezer conversion that I used for fermentation in the 50s and it is a 3F range, so I don't think I could do this. But if I ever go to a dedicated fermentation chamber I will have to consider it. Which controller are you using with the 1F range?

I have use a 1º differential and use a thermowell, I sometimes do get up to 2º over or under my set poing but I'm fine with that.

What is a thermowell?

It's a sanitary stainless tube that goes through your stopper and into the center of the wort allowing you to slide your temp probe in. It reads the middle temp of the wort.