Fermentation Station Temperature Control

[TanMan15]

Howdy homebrewers,

I'm hoping that you collective group of homebrew geniuses have a better education of thermodynamics than I do. I live in Texas and gets hot as hell around this time of the year. We're already pushing 100 degrees. I have an insulated shed where I keep a mini fridge hooked up to an inkbird temperature controller. That's where the fermentation magic happens.

After brewing a coconut cream porter this past weekend, I put my fermentation bucket into the temperature controlled fridge and set the temp to 67 with 2 degrees of variation. Instead of dropping my temperature gauge into the wort, I filled up a very small coke bottle with star sans water and dropped in there. The coke bottle is even smaller than the regular ones, I think it's half a liter.

Over the next couple of days, I checked the temperature of my wort using the temperature strip on the side of my bucket and it looked like the temp had risen to about 70 or 71, but the coke bottle was still at 67. Here's where my question comes in... is the temp gauge wrong, or is the wort temperature really rising because of the higher volume of liquid? Since the coke bottle is so small, I don't think the fridge stays on long enough to cool the wort. At the same time, I would think that the fridge would cycle more frequently, since the small coke bottle, in theory, would also heat quicker than the wort, I believe. The 5 degrees of variation is concerning, one way or the other.

Along the same note, what is a better way to do this? I'd put a larger container in there to put the gauge in, but I don't have much room. Alternatively, I'm thinking about sanitizing the hell out of my temp gauge and dropping it into the wort, through the air lock. What methods do you all use?

 

[eric19312]

I believe your readings. For two reasons.

• Volume - the larger volume of the fermentor takes longer to cool than the smaller volume of the coke bottle.
• Fermentation is exothermic - the fermenting wort in the fermentor is generating heat. The star san in the coke bottle is not generating heat. The only way the star san in the coke bottle increases in heat is if the air in the fridge warms up enough to warm up the bottle. Likely the heat that is warming the bottle is coming at least in part from the fermenting wort.

More bad news--During lag phase the problem is even worse than you think. This is after you pitch yeast and before the wort starts roiling. During lag the yeast is not producing (much) CO2, but it is active and is sensitive to temperature. But without producing CO2 it is not mixing the beer in the fermentor. So the temperature on the outside of your fermentor as measured by that LCD strip is probably different than the temperature in the middle of the fermentor.

Better way(s):

• Tape the probe to the side of the fermentor and put a piece of insulating foam (I like that stuff they sell for putting on ground under your sleeping bag) over the probe.
• Thermowell - put a thermowell into the beer and put the probe into the thermowell

TBH I think the taped to bucket and insulated over is better than the thermowell due to the lack of mixing. Taped on the outside of the bucket with insulation is probably a happy medium between the temp of the wort at the core of the bucket and the temp of the wort touching the uninsulated edge of the bucket.

I came to these conclusions based on testing wort temperatures at various points during fermentation. I bought a couple RC-4 data loggers with probes off Amazon - less than $20 each and monitored temperatures both on edge, thermowell and air in fridge over a few ferments. Did this after migrating to that 15 gallon ferment and noticing flavor issues with the beer resulting from first few batches (when I migrated I initially went with the probe in the thermowell strategy above). Probably would have been enough to ditch the thermowell and go back to the taped probe+insulation over but I found another $100 and went dual probe control...

Extra credit:
A dual probe dual stage temperature controller like this one:
http://www.auberins.com/index.php?main_page=product_info&products_id=671
or a BrewPi Spark or DIY version of the same

• One probe in the thermowell in the beer
• One probe in the air in the fridge
• One control controlling the fridge
• One control controlling a heat source in the fridge (reptile lamp is great)

You use the probe in the air in the fridge to keep the air temperature from getting too extreme while waiting for the temperature in the fermentor to catch up to set point. In that 15 gallon fermentor with a single probe dual stage controller, if my wort was 4-5 degrees from set temperature at pitch I would see significant fluctuations +/- 2 degrees F or more as the controller tried to get the temperature to target. These fluctuations would continue pretty much until the fermentation kicked in hard and started mixing the volume. With the dual probe controller I get to target with only abut 0.5F fluctuation. My controller is not PID so doesn't learn the dynamics of the system, the BrewPi and DIY versions appear to do even better but I solved my flavor issue so am happy enough with the Auber controller.

 

[kh54s10]

That is way too complicated for me. I used the insulation taped over the probe for quite a while. I had varying success at keeping the probe well insulated. I got a thermowell. I feel that is better since you are measuring the temperature of the wort in the middle where it should be the warmest. If cooling the outside would get cool first and you could be stopping the cooling by the freezer while the middle is still too warm.

But I have never thought putting the probe in a separate container was a good idea for a couple of reasons. One, you are not measuring the temperature of what you want to control. And two, I have heard that over time probes can absorb/leak into the sensor and be ruined. So mine never go in liquid.

 

[TanMan15]

So, if I were to use a thermowell with a bucket that only has only one grommet, would I have to choose between that and an airlock, or would I need to drill a second grommet?

 

[TanMan15]

So, if I were to use a thermowell with a bucket that only has only one grommet, would I have to choose between that and an airlock, or would I need to drill a second grommet?

That was a dumb question. Of course I'd have to drill another grommet...

 

[eric19312]

Thermowell really isn’t necessary. Tape probe to bucket and insulate over.