Location of temp probe

[VirginiaHops1]

I'm on brew batch #6 now and I've begun to question whether attaching my temp controller probe to the side of the fermenter is the best method. What I'm noticing is when the chest freezer turns on it shoots the fermenter temp pretty far past the target. I just pitched on my current batch this morning and set the temp at 67, I checked on it at lunch and it was at 62(chest freezer was off). I think what happens is the liquid temp moves much slower than ambient air temp, so the chest freezer is plugging along cooling and by the time the fermenter reached target temp(67), the ambient air temp is much much lower so the fermenter will continue getting colder for awhile. I just brewed last night and left the wort in the fermenter overnight to get down to pitching temp, so it's possible the chest freezer insulation is extra cold because of all that work and it will stabilize a bit. But I'm definitely seeing 3-4 degree swings throughout fermentation on prior batches.

I'm thinking a better method might be to measure ambient air temp, and put a stick-on thermometer on the fermenter to monitor that temp and I can then dial in the optimal setting. To hold 67 with the least amount of swings maybe I'd want ambient air at 62 or 63. Anyone have thoughts on this?

 

[GPP33]

Measuring the air will result in violent swings and won’t actually tell you the temp of your beer. Different beers will generate different amounts of heat so there’s no magic formula. Measure the beer using either a thermowell or better yet a long stainless temp probe so you can measure from the middle of the liquid.

You’re right that the beer will continue to cool after the freezer shuts off but due to the greater thermal mass of the beer than the air it’ll only be a fraction of a degree.

 

[VirginiaHops1]

Measuring the air will result in violent swings and won’t actually tell you the temp of your beer. Different beers will generate different amounts of heat so there’s no magic formula. Measure the beer using either a thermowell or better yet a long stainless temp probe so you can measure from the middle of the liquid.

You’re right that the beer will continue to cool after the freezer shuts off but due to the greater thermal mass of the beer than the air it’ll only be a fraction of a degree.

Regarding the bolded, I know. The idea would be to put a thermometer on the fermenter and monitor it's temp myself, to dial in what is the proper ambient air temp needed. Similar to dialing in boil-off or any other variable by a bit of trial and error.

Can you explain how this would result in more violent swings of fermenter temp? You can hold your air temp very steady. You'd obviously keep it lower than target fermenter temp, and monitor the fermenter temp and adjust accordingly. Amount of heat given off would vary but I primarily brew IPAs right now so if the process worked I could apply it to most of my beers.

 

[mongoose33]

Here's how I measure temp on my fermenters:

I take a piece of closed-cell foam, cut a small channel into which the temp probe will lie. Then I use a bungee cord--but you can use string, whatever holds it fast--to hold it to the side of the fermenter. That way it's taking the temp from the fermenter and not from ambient. Other types of insulation could be used, too.

You'll see in the pic below that I have both blue and pink foam I'm using to isolate the temp probe from ambient and get the temp of the wort. If you've isolated the probe well from ambient, my view is that it isn't materially different than a thermowell.

 

[VirginiaHops1]

Mongoose, that's basically what I do. I saved some packing insulation from some package we got and I tape it to the fermenter with painters tape, and slide the probe inside it. I'm confident I'm measuring the wort temp very accurately, I'm just seeing bigger swings in it's temp than I'd like because the chest freezer cools down the ambient air much quicker than the big jug of liquid, so once the wort hits target temp and the freezer shuts off it's sitting in a cold box where its temp will continue dropping.

I'm not really worried about the 3-5 degree swings messing up my beer, but like everything else I'm always trying to do these things in the best/most efficient manner.

 

[Nokt]

What kind of controller do you have? Does it have the ability to run a heat source as well or just cooling?

 

[mongoose33]

Mongoose, that's basically what I do. I saved some packing insulation from some package we got and I tape it to the fermenter with painters tape, and slide the probe inside it. I'm confident I'm measuring the wort temp very accurately, I'm just seeing bigger swings in it's temp than I'd like because the chest freezer cools down the ambient air much quicker than the big jug of liquid, so once the wort hits target temp and the freezer shuts off it's sitting in a cold box where its temp will continue dropping.

I'm not really worried about the 3-5 degree swings messing up my beer, but like everything else I'm always trying to do these things in the best/most efficient manner.

Here's the problem: once the air temp in the freezer reaches the set point, the compressor turns off. BUT, it doesn't stop cooling. The freezer coils are still very cold, so it will continue to cool until the coils and air temp reach an equilibrium (not accounting for warming from ambient outside the freezer, of course). So you'll tend to overshoot the target if you're measuring based on ambient air temp.

The air in the freezer will warm much, much faster (the opposite of what you note above), so that air is warming and cooling far faster than the wort. But that's OK.

If you're seeing big swings in the wort temp, I'd tend to see the insulation over the probe as the culprit.

 

[VirginiaHops1]

I've got a little digital temperature gauge, that keeps track of high/low temps. Maybe I'll do an experiment and put it in the chest freezer, and set the probe to measure ambient air. I'll be able to see if the freezer can hold a pretty steady temperature or there's a lot of fluctuation.

Nokt - I use the Inkbird so yeah it can control a heating element if I need it to. I've thought about trying that. It sits in a room where the temperature is 75-80 during the summer though, so I shouldn't really NEED it. And I like to keep things as simple as possible.

 

[GPP33]

Regarding the bolded, I know. The idea would be to put a thermometer on the fermenter and monitor it's temp myself, to dial in what is the proper ambient air temp needed. Similar to dialing in boil-off or any other variable by a bit of trial and error.

Can you explain how this would result in more violent swings of fermenter temp? You can hold your air temp very steady. You'd obviously keep it lower than target fermenter temp, and monitor the fermenter temp and adjust accordingly. Amount of heat given off would vary but I primarily brew IPAs right now so if the process worked I could apply it to most of my beers.

The temp swings I was referring too are in the air, not the beer. Air changes temp rapidly, liquid not so much, thermal mass.....My point was that the temp reading will vary mroe but your beer temp will remain consistent as it probably currently does. The result will be rapid cycling of your compressor which isn't good for it. I also wouldn't assume that all IPAs will ferment with the same vigor, I've had some ferment slowly and others be visually done in 48 hours. Not sure how that would have affected heat generation but I think it's a broad assumption to say they would be the same.

I've got a little digital temperature gauge, that keeps track of high/low temps. Maybe I'll do an experiment and put it in the chest freezer, and set the probe to measure ambient air. I'll be able to see if the freezer can hold a pretty steady temperature or there's a lot of fluctuation.

Nokt - I use the Inkbird so yeah it can control a heating element if I need it to. I've thought about trying that. It sits in a room where the temperature is 75-80 during the summer though, so I shouldn't really NEED it. And I like to keep things as simple as possible.

I use a heating pad to counteract the residual chilling effect from the thermal mass in the freezer, it can easily heat the air and bring a stop to cooling wort, it doesn't do much for heating wort up though.

I also wouldn't assume that an exterior thermometer will read the same as an internal thermometer. It's on the outside, it's better than hanging in air but not as good as being surrounded by beer. As I said earlier, the temp swings you are currently seeing are probably artificially high. If you're using an inkbird get one of these and run it through a 1/4" grommet.

https://www.amazon.com/dp/B01A6DIPFM/?tag=skimlinks_replacement-20

 

[NinjaBear]

I put my probe directly into the beer…

 

[RPh_Guy]

Where you put your probe is your own business

 

[TerpRush]

Here's how I measure temp on my fermenters:

I take a piece of closed-cell foam, cut a small channel into which the temp probe will lie. Then I use a bungee cord--but you can use string, whatever holds it fast--to hold it to the side of the fermenter. That way it's taking the temp from the fermenter and not from ambient. Other types of insulation could be used, too.

You'll see in the pic below that I have both blue and pink foam I'm using to isolate the temp probe from ambient and get the temp of the wort. If you've isolated the probe well from ambient, my view is that it isn't materially different than a thermowell.

This +100

 

[cristinikol]

you can try a weldless thermowell. it's about 8 dollars and you can install it yourself. works great and it's easy to clean/remove

 

[VirginiaHops1]

Appreciate the suggestions guys. I'll keep tinkering with the setup and hopefully can decrease the temperature swings a bit.

 

[ThePaleAleIndian]

I'm on brew batch #6 now and I've begun to question whether attaching my temp controller probe to the side of the fermenter is the best method. What I'm noticing is when the chest freezer turns on it shoots the fermenter temp pretty far past the target. I just pitched on my current batch this morning and set the temp at 67, I checked on it at lunch and it was at 62(chest freezer was off). I think what happens is the liquid temp moves much slower than ambient air temp, so the chest freezer is plugging along cooling and by the time the fermenter reached target temp(67), the ambient air temp is much much lower so the fermenter will continue getting colder for awhile. I just brewed last night and left the wort in the fermenter overnight to get down to pitching temp, so it's possible the chest freezer insulation is extra cold because of all that work and it will stabilize a bit. But I'm definitely seeing 3-4 degree swings throughout fermentation on prior batches.

I'm thinking a better method might be to measure ambient air temp, and put a stick-on thermometer on the fermenter to monitor that temp and I can then dial in the optimal setting. To hold 67 with the least amount of swings maybe I'd want ambient air at 62 or 63. Anyone have thoughts on this?

Fwiw, I control my ambient temperature for fear of the exact issue you're describing. Here is my process, loosely:

I am a stickler about my pre-pitch wort temp. I chill down to my desired temp, pumping ice water if needed, transfer to the fermenter and place immediately in my keezer, where I initially control the ambient temp to the same as pitching temp. I typically pitch fairly cold, many ales at 60F and lagers at 45F. I have never seen a rise-over-ambient quoted at more than maybe 8F, and 68F and 53F are both still respectable for ales and lagers respectively towards the end of fermentation. By the end of active fermentation, I raise the ambient temp in my keezer to 5-8F above my pitching temp.

I've found this is a good way to control the beer temp without temp swings. Yes, I don't know EXACTLY what the temp of my beer is at all points of fermentation. But this method controls the temp in a very narrow range and avoids the large temp swings you're describing. Makes great beer, and I've never had an issue with stalled ferments.

However, as I mentioned, you do have to be pretty particular about your pitching temp, because this whole thing hinges on the laws of heat transfer witb that pitching temp as your initial condition.

Just my $0.02.