Fermentation Chamber Temp Probe Placement

[SamInNJ]

I'm currently working on building a fermentation chamber to hold at least 4 buckets/carboys so I can brew every couple weeks and have plenty of room. I've been thinking a bit about where to place the fermentation temp probe and am not entirely sold on any of the options I can think of.

Hanging in the fridge free->
Measures ambient. Will have more fluxuation and on/off switching of the freezer. Would be 'unbiased' in that it wouldnt be heavily influenced by a given fermenter (if one is in day 2 it will be hotter from the fermentation process than one that is in week 3 and about to be bottled).

Placed INSIDE a fermentor->
Biased to a specific fermentor, could negatively impact other fermentors. Due to large thermal mass of the beer, would cause ambient to get MUCH lower than the inner temp by the time the inner temp hit the target temp, causing it to continue to cool over time.

Taped to a fermentor ->
biased to that fermenter. Otherwise seems in between the first two options. Kind of what I'm leaning towards. Somewhat biased to the stage of the fermentation that it is attached to.

Taped to a carboy of water ->
no bias, would let actively fermenting buckets to go a little bit over, but would also keep the freezer temp relatively stable.

Anybody have strong opinions on this?

 

[kombat]

The "best" way is inside the beer itself, with a thermowell. That's the best way to measure the actual temperature of the beer itself, right in its core.

Granted, this makes it impractical to ferment more than one fermenter in the same chamber. However, if they are basically the same batch, at the same point in their fermentation cycles, they should remain relatively close together in terms of temperature.

In my own setup, each beer gets its own fermentation chamber. I have 2 freezers, each with its own STC-1000, heating belt, and thermowell stopper. I ferment all beers for 2 weeks before removing from the chamber. This effectively limits me to one batch per weekend. If I'm doing a double-brew-day, I just don't brew the weekend prior.

 

[SamInNJ]

Have you run into an issue where by the time the center of the beer gets to your target temp, that the air in the rest of the chamber is much cooler, so the beer would keep cooling past the target point causing your heater to turn back on? I feel like that could create a loop where it's always heating/cooling trying to chase the lag time it takes to heat/cool the actual beer.

 

[kombat]

Have you run into an issue where by the time the center of the beer gets to your target temp, that the air in the rest of the chamber is much cooler

Yes, of course this will happen, but ...

so the beer would keep cooling past the target point causing your heater to turn back on?

In practice, this does not happen. The reason is that the beer has a far, far higher thermal mass than the air inside the freezer.

If your beer is too warm, the temperature controller will turn on the freezer. Since the beer takes a long time to cool, the freezer pretty much runs like a normal freezer would, cooling all the way down to normal freezer temperature. So the air inside the freezer is 20° F or whatever, while the beer comes down to the target temperature.

Finally, the beer is at the right temperature, and the temperature controller kills the power to the freezer. But the air inside the freezer is still 20° F. The beer slowly cools a little bit more, as the freezer warms up. But since the beer has such a drastically higher thermal mass, it cools much more slowly than the air warms up.

I set my temperature control with a pretty tight tolerance (0.3° C). Occasionally, I notice that the temperature has indeed drifted too low, and the heating circuit kicks on. I have a heating belt wrapping my carboy, and plugged into the heating circuit.

The end result is that my beer always stays within +/- 0.5° C of the target temperature.

I feel like that could create a loop where it's always heating/cooling trying to chase the lag time it takes to heat/cool the actual beer.

Also keep in mind that you can change the "delay" setting of the temperature controller. I have mine set to 10 minutes. That means that if the controller has turned on the freezer at all within the last 10 minutes, it will not turn it on again until at least 10 minutes have passed, regardless of how warm the beer may be getting. This is to protect the freezer's compressor.

 

[SamInNJ]

Thanks Kombat, thats hugely helpful!