Question about fermentation temp (with chest freezer)

[DVCNick]

So I got the requisite craigslist chest freezer over the weekend. My intent for now is to have it be a fermentation chamber, though it could be converted to a kegerator later if desired.

Anyhow... So far I have one carboy in it which is already past a week fermenting. I have the temp controller set to 70. I have the temp probe measuring beer temp in a thermowell. The temp range is set to +/- one degree (I think the tightest you can set on the Inkbird)

When the cool kicks on, it of course goes until the temp drops to the cutoff point of, I want to say, 69.0. But that is the internal beer temp in the center of the carboy, and even after the freezer kicks off, the indicated temp continues to drop, all the way to about 66. At the current heat level in the house I think this would cycle approximately once a day if I stopped messing with it (opening the lid, etc).

Is this bad? I guess I was expecting a more consistent and fine tuned level of control here.

Once I'm confident the beer is at the right temp, should I take the probe out and suspend it in the middle of the chamber, measuring air temp instead?

I think I'm going to do some side by side comparisons over the next couple of days, hanging my other temp controller probe in the middle of the chamber and see how they compare.

 

[balrog]

Overshoot is the trouble with the simple controller, no doubt about it.
That's why some folks go to "PID" (proportional/integral/derivative) controllers that can "learn" over a few cycles to not overshoot. They cut off cooling with the learning that downward trend will continue a bit.

Sometimes just adding a fan to the inside of the chamber helps.
Sometimes adding some thermal mass (another bucket full of water) helps.
Sometimes putting a box, towel, thinsulite mat, something under the carboy to get it off the metal floor of the chamber helps.

 

[snarf7]

I wouldn't put the probe in your beer, the risk of contanimation isn't worth it. Instead fill a 2 lt bottle with water, get it propped up in the center of the keezer so the probe is more or less dead center and you should get a pretty accurate reading of the internal temp of the keezer. Be aware though that the fermentation process generates heat so the temp inside the fermenter will be warmer than the air around it, that's OK and to be expected.

And to answer your question about it cycling a few degrees, no that's not a big deal, the whole process is quite forgiving as long as you're not cycling all over the place with your temps. What I recommend is starting out your yeast at the optimal temp listed on the package, let it get going (24-36 hrs usually its kicking) then slowly bring it down a little to the lower end of the temp range for your yeast. That will prevent any off flavors from developing and the yeast will chug away just fine.

For example, take US05 it's range is 64-82. So right now room temp in my house is around 72-74 usually, I'd pitch at that temp, let the yeast get going then out it in my basement at around 66-67 and let it finish up there.

 

[DVCNick]

Probe is currently in a thermowell that is sanitized before going in and stays there throughout the fermentation (or at least the vast majority of it) so I don't consider the risk of infection significant.

If the overshoot by 3 degrees and cycling once or twice a day is not going to result in negative impact to the beer, I'm happy to let it go as-is.

However, I'm thinking that once the beer is in the ballpark of the right temp, and definitely after the most rigorous part of the fermentation is over, running the controller based on the ambient air temp will result in less overshoot and more precise control? I've got two inkbirds that register very close to each other, so I can do some experimenting (thermowell vs. ambient) with my current beer that is on the tail end of active fermentation.

 

[snarf7]

Yeah just play around with it, as long as it's not running way too hot you'll be fine

 

[cswant88]

The 3-4 degree swing isn’t going to ruin your beer. I’d leave the probe in the beer. The beer temp is what you want to regulate, air temp is meaningless. You can try setting your fermenter on some pieces of wood, just to be sure it’s not absorbing any residual cold from the metal walls of the freezer. Also try a dab of thermal grease on the probe before you stick it down the thermowell. This may make the probe a little more responsive and minimize the swing.

 

[DVCNick]

Makes sense.

Doing some observations of the beer vs. air temp, it is behaving as I thought it would. So far I'm regulating based on the beer temp and also measuring the air temp for comparison.

When the compressor kicks on, the air temp starts dropping rapidly, the beer temp is dropping but lagging the air temp drop by a lot, and the compressor kicks off once the beer temp hits the threshold. The air temp is a LOT lower by then and therefore the beer temp continues to drop (maybe an extra three degrees). By the time the beer temp ramps back up near the max temp allowed (takes a while) the air temp is back to within one degree of the beer temp.

I think I could regulate on the air temp instead, and also measure the beer temp to confirm this: I think regulating based on the air temp would keep the beer bang on the intended temp; it would just cycle the compressor a lot more often. Probably not the best for the freezer. (and of course the beer temp might be just a little over during the most active part of the fermentation doing it this way).

One other issue I have that doesn't seem to be a thing for other people: My immersion chiller only gets my wort down to about 110 or so before it becomes very inefficient. I don't know how much longer it would take to get much below that, but I'm not willing to send enough water down the driveway to find out. What I've been doing is putting it in the fermenter at about 100F and then chilling it down in my swamp cooler, but, it is not fully submerged and this leads to a very layered temp that persists for quite a while. The submerged part might be at pitching temp, but the top layer could still be at 85 or higher and it will stay that way for a while. Usually I've been pitching the next morning.

I'm looking forward to seeing how fast this freezer can get me from 100ish to pitching temp, and it will be uniform since the whole carboy is in there.

 

[balrog]

There's an art to temp probe placement sometimes, wherein I find with just a hint less than superduper probe coverage on the outside wall of the fermvessel, allowing it to "see" the chamber temp a teeny bit, allows the simple Inkbird/STC type controllers kick off sooner that if the temp probe were highly insulated from chamber temp.

 

[Beernik]

There are a couple things:
1) air is an insulator, you need a fan to circulate it. What I think is happening is the walls of the freezer are getting really cold and that mass of cold is what continues to drop the temperature of the chamber. In the least, you need a fan running while the cold cycle is running to keep the air, the walls, and the beer at the same temperature.
2) a dual stage controller (hot cycle and cold cycle) is better for fermentation control. For this type of controller, you want your fan more-or-less running all the time. Your heat source can be something as simple as a brew belt laying inside the freezer.

As for cooling your wort, the efficiency of an IC Is heavily dependent on the temperature of your tap water. If it comes in at 70 or 80F, like in Phoenix in the summer, your going to struggle with an IC unless you get a pre-chiller.

Even if you don’t have warm groundwater, it’s a lot easier to go from boiling to 100F than it is to go from 100F to 70F. One of the drivers of efficiency is the temperature difference. I use an IC in a bucket of ice water as a pre-chiller for the IC I put in the wort to get the temp down to 80F, transfer, and stick the bucket in the ferm chamber to drop it the rest of the way to pitching temperature.

 

[snarf7]

Yep, fans are essential to keep everything moving, you don't need much, one of these little computer fans will do the trick: https://www.amazon.com/gp/product/B00G059G86/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I have one pointing downward and another pointing sideways and i find it works well, I can take the temp anywhere in the chamber and it's within 0.5 degrees F

 

[brew703]

Fermentation temp is most important at the beginning of the fermentation process. I usually take the low end of the yeast range and set my Inkbird 2 degrees above. Once I am past 4-5 days of fermentation i start raising the temps until i hit 68 and let it there to finish fermenting.
As others have said, a small temp swing isnt going to hurt unless it drops too low and it stops fermentation or too high where it may produce some off flavors.
I also use a thermowell through the lid of my brew bucket and I find that has worked the best for me during fermentation.

 

[CascadesBrewer]

I have my temp probe taped to the side of my fermenter, and honestly I feel this is better than either a thermowell or hanging loose. Yeah, the temp of the probe will be influenced some by the temp of the air in the chamber, but that is kind of the point...it will help with the overshoot that are bound to happen with a thermowell.

I find that it takes me about 3 hours to drop my fermenter down from around 80F to 65F. I also chill my wort down to the 90F to 100F range, then transfer to my fermenter. If you don't have a heater in your chamber, just keep in mind that it will likely overshoot by 5F or more.