Carboy tape thermometer vs. actual temp

Carboy tape thermometers; pretty accurate, for your secondary fermenter. But isn’t it the case that, during primary fermentation, the tape thermometers aren’t picking up on all that 'exothermia' at the core of the carboy?

If I’m correctly informed on this, is there any information out there as to what the difference is between what the tape says and what is actually going on in there? Is a rule of thumb or safe range available?

Eventually I’m going to get myself a fermentation chamber of some sort, and if I can control things, it makes sense that I should know where I should be controlling them to.

well the warm wort will heat the carboy. the warmed carboy will heat the stick on thermometer giving you a reasonably accurate reading. besides all the stick-ons i've seen only give a 2 degree resolution so they are not going to be that accurate anyway. the difference between the middle and outside of an active fermentation isn't going to be more than a degree or so.

if your really worried about that degree difference (and you shouldn't be) get a thermowell and a temp controller with a probe that will fit down inside it. you may have to sand the probe a little to get it to fit. that way you know your getting the temp from the middle and warmest part of the wort.

TipsyDragon said:

the difference between the middle and outside of an active fermentation isn't going to be more than a degree or so.

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That is not a big difference. I was imagining something much more severe, in the 5-6 degree range.

TipsyDragon said:

if your really worried about that degree difference (and you shouldn't be)

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The extent of my worry is directly proportional to the size of the difference. If the difference is really only a degree or two...

I'm not worried.

Keep in mind that all of the fermentation activity actually "churns" the wort around, so while the temperature of the fermenting beer is higher than ambient, there isn't much of a difference in the beer itself.

YooperBrew said:

Keep in mind that all of the fermentation activity actually "churns" the wort around, so while the temperature of the fermenting beer is higher than ambient, there isn't much of a difference in the beer itself.

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Sorry to mince words, but my question was not "ambient vs. ferment", but rather "tape thermometer vs. ferment", which I suppose can also be posed as "glass vs. ferment".

But your point, I think, is that the tape thermometer is going to be just as accurate during high activity (due to all the churning) as it will be after activity has subsided?

Yeah, I was listening to an older Brewing Network podcast recently and they reported that they collected data and the average difference between thermowell & stickon thermometers was on average less than .5 degrees F. So I think it'll do you just fine.

I'm glad that myth is finally debunked!

Fantastic!

Judochop said:

Sorry to mince words, but my question was not "ambient vs. ferment", but rather "tape thermometer vs. ferment", which I suppose can also be posed as "glass vs. ferment".

But your point, I think, is that the tape thermometer is going to be just as accurate during high activity (due to all the churning) as it will be after activity has subsided?

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Yes, that is exactly what I said. The contant churning of the beer fermenting means that there would be very little, if any, temperature differential between the inside and the outside of the liquid. Also, 5 gallons of liquid has a very high thermal mass, so even when fermentation slows or stops, it is very close in temperature throughout. To make it even more so, especially in the summer, you can add a water bath. I do that- put the fermenter in a cooler in a water bath. It takes a LONG time and a huge temperature hike to change the temperature of that much liquid. So, often a floating thermometer in the water bath will read within 1 degree of the temperature inside the middle of the carboy.