Fermometer temps in cooled chamber

Hi all,

I want to get some input on how exactly fermometers work, and how accurate they are in reading the wort's/beer's temp in a cooled environment.

Reason I ask is, after having the A/C of my cooled chamber on for about 30 minutes tonight, I noticed that the fermometer's temp dropped from 70F-72F to 66F-68F. That seems like quite a big drop in temp for 5.5 gallons of fermenting beer, given the short amount of time.

If the ambient temperature of the chamber drops to 66F on a regular basis, will the fermometer attached to each bucket also read similar temps, regardless of the real temp of the wort/beer? If so, what's the best way to mitigate this affect? Should I stick the temperature probe of my external tstat (once it comes in this week) to the newest fermenting bucket and secure it with a few layers of gorilla tape or some great stuff foam?

Regardless of what thermometer you use, you're going to have incorrect readings unless it's actually submerged in the beer. The Fermometer is nice, but it's only giving you an average between the room and the bucket. So if the room is 68 and your fermenting wort is 74, then the fermometer will probably read around 71. It's attatched to plastic or glass...which both cool a lot faster than liquid.

Those fermometers are crap. Rub your thumb across it, and it jumps 10 degrees. IMO, it's reading an average between carboy temp (which will be different than beer temp by a bit), and air temp, NOT beer temp.

Best way is put your probe in the beer, but that's pretty iffy, since you will have more than one carboy of beer in your chamber, and they will be at different stages of fermentation, and therefore putting out different amounts of heat.

I think the easiest thing to do is to stick your probe in a 500 ml pop bottle filled with water. You get a good solid temp reading that way, you aren't subject to random temperature swings due to cool air blasting around, and you don't have to worry about transfering the probe from carboy to carboy. The temperature of the pop bottle will be 0-10 degrees cooler than your carboys, because there's no fermentation in your pop bottle. Just compensate for that. Want your beer to ferment at 68? Set the probe for ~60-63, and you should be in the right range.

The only way to accurately control fermentation temp of more than one carboy in a chamber at the same time would be to wrap each carboy in a glycol cooled jacket, and individually control jacket temps with individual probes in each carboy, which sounds to me like a major undertaking.

Alright, thanks for the advice. I'll try the pop bottle trick.

For what it's worth, on the BrewStrong podcast Jamil Z and John Palmer suggests you tape your thermometer against the side of your carboy and then insulate it with foam or a towel against the air. They think that the heat of yeast sex is significant enough to not use the thermometer-in-a-yeast-tube approach.

I have no idea, personally, but Palmer and Jamil have won a few awards.

Old thread but I've been wondering a lot about this.

I have a fermentation fridge and an STC-1000, and I ferment in glass carboys.

I always notice that an active fermentation is 3 to 4 degrees warmer – by the fermometer – than a carboy sitting next to it that has finished. I have put a thermometer into the fridge with the carboys (my metal one with a rod and a clip for the rim of a kettle, which I calibrate) to see what the air temp is compared to what the fermometers say. It fluctuates more than the carboys, as you’d expect, but it seems consistent with the temps I see on the fermometers - about a degree lower than the carboy I've taped the probe to.

I wonder if the middle of the carboy is much warmer than the outside, and if the air touching the stick-ons could cool them enough to where they show 65, while the fermentation is actually 66 or 67. It stirs around a ton, obviously, so it seems like it would be fairly consistent. But I don’t know. Somebody out there has probably measured the inside of a carboy… but I don’t want to assume…

Between the STC-1000 temp setting, the fermometers and how they read with active/complete fermentations, and an ambient thermometer reading, I think they are fairly accurate - I think the inside of my carboy is pretty close to the number on the fermometer. But what if I'm wrong...

So, has anybody checked into this further?

I know this is an old thread, but perhaps it will be of help to someone.

Suthrncomfrt1884 said:

Regardless of what thermometer you use, you're going to have incorrect readings unless it's actually submerged in the beer. The Fermometer is nice, but it's only giving you an average between the room and the bucket. So if the room is 68 and your fermenting wort is 74, then the fermometer will probably read around 71. It's attatched to plastic or glass...which both cool a lot faster than liquid.

Click to expand...

See my comment below.

Red Clay said:

For what it's worth, on the BrewStrong podcast Jamil Z and John Palmer suggests you tape your thermometer against the side of your carboy and then insulate it with foam or a towel against the air. They think that the heat of yeast sex is significant enough to not use the thermometer-in-a-yeast-tube approach.

I have no idea, personally, but Palmer and Jamil have won a few awards.

Click to expand...

I do not expect Jamil to know jack squat other than how BJCP judges judge beers, but Palmer should know this:

Fermometers are accurate to within 1˚F for every 10˚F difference in actual air temperature. As an example if your Fermometer reads 65˚F and your room temp is 75˚F then the actual temp of fermenting wort is closer to 66˚F.

Here is the product page:
http://tkachenterprises.com/Products.html

You can easily check this at home by filling your fermentor with tap water, inserting a 12" dial thermometer "through the top", and checking the difference once both thermometers have reached equilibrium.

Crucial-BBQ said:

I know this is an old thread, but perhaps it will be of help to someone.

See my comment below.

I do not expect Jamil to know jack squat other than how BJCP judges judge beers, but Palmer should know this:

Fermometers are accurate to within 1˚F for every 10˚F difference in actual air temperature. As an example if your Fermometer reads 65˚F and your room temp is 75˚F then the actual temp of fermenting wort is closer to 66˚F.

Here is the product page:
http://tkachenterprises.com/Products.html

You can easily check this at home by filling your fermentor with tap water, inserting a 12" dial thermometer "through the top", and checking the difference once both thermometers have reached equilibrium.

Click to expand...

FWIW Jamil advises that people should be measuring their wort with a thermowell...especially if your controlling a chamber based on it the thermowell will always give you the most accurate reading...and honestly they arent that damn expensive, you can get them for $12 from BrewersHardware, so theres really no excuse if you've spent $50-200+ dollars on a ferm chamber to not use a thermowell. Shove the thermowell into a drilled stopper, or a carboy cap and be done with wondering how accurate your temperature readings are.

Thanks for the info on the thermowell, that is exactly what I need