Measuring & Controlling Fermentation Temperature

Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum

Help Support Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Bearcat Brewmeister

Pour, Drink, Pee, Repeat
HBT Supporter
Joined
Feb 20, 2006
Messages
694
Reaction score
28
Location
Gaitherburg, MD
Since this now seems like the fermentation forum, I have another one. How does everyone out there measure their fermentation temperature accurately? I use one of the sticky thermometers on the side of the carboy as well as an indoor/outdoor thermometer, with the outdoor "probe" pressed against the side of the carboy and the indoor part (the actual base unit) a few feet away to measure ambient air temperature. Until this batch, I fermented in my basement or on the basement steps, depending on the temperature I needed (the top of the steps is about 70F and the basement floor is 64F in summer and in the upper 50s in winter).

My concern is that the outside of the carboy is not very accurate for measuring temperature. Is the sticky thermometer only taking the temperature of the glass touching it (which is presumably the temperature of the wort directly behind it) or is it influenced by the ambient air temperture (which should be cooler since the yeast activity in the wort is generating heat)? Do any of you use thermometers inside the fermenter? If so, how far down in the fermenter is the temperature being taken? I know a Ph.D. in microbiology and he said that in a fluid with yeast fermenting, there will be a difference in temperature at different depths within the liquid, possibly up to a few degrees.

I ask all of this since I am having a hard time keeping the fermentation temperature down in my Scotch Ale. With the high gravity, the yeast activity is strong and it is generating quite a bit of heat, too much to just let it sit on the basement floor. I fortunately just finished my freezer conversion, so I had it available for the fermenter. I set my fridge to 60F and verified the fridge temperature with my other thermometer, yet the carboy sticky thermometer read 65F, and I feared that the internal wort temperature may even be higher. I turned the temperature down to 58F and after a day and some slight slowing in yeast activity, the sticky thermometer reads 61F to 62F.

Any sharing of expertise/experience would be greatly appreciated.
 
Yes, absolutely a vigorous ferment will raise the temperature of your beer above ambient temperature. That's why it is important to measure the beer temp and not air temp.

I use the same method of fixing a remote temperature probe to the carboy with great success. The only thing you have to do is insulate it from the air. I use some 1/2" foam around the probe, but really you could use anything that acts as an insulator.

And I don't like those sticky thermometers. They are hard to read precisely, and they aren't going to read beer temp unless you insulate them well, too, which defeats the purpose since you won't be able to see them to read the temp.
 
i use the same in/out thermometer taped to my carboy in the fermentation chiller. every time i've tested it, it's came out pretty much the same as my fermometer.

I love the 24 hour high/low reading! I've been keeping my beer between 65.1 and 66.9 for the last couple weeks.
 
So if you are shooting for a target fermentation temperature, how much cooler do you have the ambient temperature at the start of fermentation? I figure the gap from ambient to wort temperature is greatest at the height of fermentation, say 12 to 36 hours after it kicks off and the gap decreases as fermentation slows.

Until recently, I have not had issues since I brewed beers at or below 1.060 and the gap at start up was about 2 degrees. I recently started making IPAs over 1.070 that had vigorous fermentations that raised my temperature too high (gap of 4 degrees ambient to wort) and I had overly fruity beer. Now I have a Scotch Ale and I am working hard to keep it cool enough. Just wondering if anyone had a rule of thumb based on SG as to how much of a gap in temperature to expect.
 
IMO the indoor outdoor, and even the stick ons are not going to be accurate enough for some styles, and would probably affect repeatability. The surface temp of the vessel is going to be a kind of average between the ambient and the centre of the ferment, since the ambient is "touching" the thermometer.
I drilled a hole in the top of my fermenter, made a well with a length of 1/2 inch copper pipe and a bulkhead fitting to isolate from the outside, and I drop probe into the well. That way I am measuring the centre of the ferment.
Cheers.
 
I copied a few ideas from this forum and covered a probe thermometer with tubing. I then placed it in the middle of my fermentation through the second hole in my carboy cap. I use a wort chiller cabinet. I studied the ambient temp outside, inside the chiller, and inside the ferment. I also had a sticky on the side. There was approximatly a 6 degree difference in my fermentation 36 post pitch from the chiller temp. I find that I have to set the chiller thermostat to 62F to get a 68 fermentation temp. Interesting enough, the sticky thermometer was inline with my probe inside the ferment. That was enough for me to trust it. I don't think fractions of a degree matter much as long as the beer-to-be is kept below 68 or so.
 
Mr. Mojo Rising said:
There was approximatly a 6 degree difference in my fermentation 36 post pitch from the chiller temp. I find that I have to set the chiller thermostat to 62F to get a 68 fermentation temp.

So if your chiller has a thermostat with a 4 degree differential, then the temp would cycle from 58F to 62F when set to 62F and the average ambient would be 60F, so wouldn't that be an 8 degree differenece to the wort? Or is your differential on the plus side of the set temp?
 
I use a thermowell probe with a Ranco controller. The probe is in the wort, and the controller can add heat via a Fermwrap wrapped around the carboy, or cool via the fridge that the carboy is sitting in.
 
Last year a bunch of us compared side temperatures to liquid temperatures & found no difference within the accuracy of our equipment (for mine 0.5F). I've also compared the temperature at various levels and did not see any stratification until the ferment was almost complete. Your biggest problem is that sticky, as mentioned.
 
Jester369 said:
I use a thermowell probe with a Ranco controller. The probe is in the wort, and the controller can add heat via a Fermwrap wrapped around the carboy, or cool via the fridge that the carboy is sitting in.

This seems to be the optimal solution. Did you specially modify a vinyl blow cap to accommodate the probe? Can you post some pictures of your set-up? To me, if this can be done without risk of contamination this is the way to go. Your controller is actually controlling the temp of your beer throughout the fermentation process prior to secondary storage. I am getting ready to order two brewers edge controllers with the probe and heat package to control temp throughout the brewing process. I imagine the heater will rarely be needed in my neck of the woods.
 
I drilled a small hole undersized slightly from the diameter of a long stemmed thermometer into the plastic bucket primary lid. I just stick a sanitized thermometer into the hole. Reads smack in the middle of the liquid.
 
bpcsatx said:
This seems to be the optimal solution. Did you specially modify a vinyl blow cap to accommodate the probe? Can you post some pictures of your set-up? To me, if this can be done without risk of contamination this is the way to go. Your controller is actually controlling the temp of your beer throughout the fermentation process prior to secondary storage. I am getting ready to order two brewers edge controllers with the probe and heat package to control temp throughout the brewing process. I imagine the heater will rarely be needed in my neck of the woods.

I actually don't have any pix of it set up, but it's pretty simple. I took a carboy cap and stuck the thermowell tube in the airlock hole (it wouldn't fit in the other nipple), and taped around to seal it up - it wasn't a super tight fit so I wanted the extra protection. Then I run a blow off tube off the other nipple. The only downside is that the carboy cap nipples are so small that the blowoff tube can't be very big. I have a couple of new undrilled rubber stoppers on the way that I am going to drill specially for the thermowell and a nice big blow off tube. I'll post up a pic when it's done.

Wow -I said nipples like 3 times and never meant anything dirty about it! :drunk:
 
I'd just like to tack the following onto this discussion:

Some yeasts are extremely temperature sensitive, and you may have to control temperature quite precisely in order to get the desired results. (Hefeweizen yeasts, for example, can yield quite different flavor results if fermented a degree lower or higher. And many Belgian strains will get stuck if they go below 65 F)

However, temperature stability is generally much more important to good brewing results than absolute temperature control. Basements are great in this regard: even if it's a degree or three above or below the ideal temp, steady temps over the course of active fermentation will yield maximal results.
 
cweston said:
However, temperature stability is generally much more important to good brewing results than absolute temperature control. Basements are great in this regard: even if it's a degree or three above or below the ideal temp, steady temps over the course of active fermentation will yield maximal results.


I couldn't agree more. :fro:
 
Resurrection of an ancient thread, but seemed the best in my search. From what I gather even though I ferment in my basement, which fluctuates a few degrees. I Just so happen to ferment in a nice protected spot which just so happens to be in a laundry sink that never gets used. I should fill the sink with water to keep the temps more stable due to the additional thermal mass?

Follow-up question is this more important in primary fermentation or secondary? I'm not sure I have room for the ale pail and a carboy or 3.
 
Yes, the extra thermal mass helps dampen the temperature fluctuations. You can use ice packs or an aquarium heater to help control them more yet if necessary. The critical time for off flavors is the initial 2 to 4 days as the yeast propagate and go through the fast part of the ferment while there is a lot of sugars present. Once the ferment slows you can let it warm to room temperature which may help get to the proper final gravity and take care of some of the esters that give off flavors.
 
My temps fluctuate in great ale temps 62 to 68, but if I can make it better by adding a few gallons of water to the 'shelf' I ferment on why not. Looks like i can only fit one container so primary it is.
 
Back
Top