How to get accurate temp reading of fermenting beer?

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Superdave

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So I've got a freezer setup for fermentation and a ranco temp controller to control it.

I am aware that the act of fermentation causes the beer to be a few degrees warmer than ambient. I know many people just stick the temp probe into the fermenting beer to get an accurate reading, and I have done this before as well.

I'm always a bit nervous though about keeping the probe sanitized, so here's what I'm thinking:

After pitching yeast, put a bit of sacrificial beer into a wine bottle or some such, and stick the probe in that.

Do you think that would result in an accurate temp reading of the carboys full of beer?

Other ways to get accurate temps of the fermenting beer without actually putting the probe in it?
 
You can place the temperature probe on the outside of the carboy. Tape it securely and place some insulating material on top of it. This will accurately read the temperature of the fermenting beer.

Using a smaller volume in a wine bottle like you suggest will probably not be the same temperature as the beer in the carboy because of the smaller mass and higher surface to volume ratio.

-Steve
 
Perfect! I was kinda thinking the same thing about the smaller amount, though it does seem like it would be better than a probe just in the air and guessing how much lower than desired temp to set the controller.

Suggested insulating material that would attach easily to the carboy? Any other ideas anyone?
 
It's probably overkill, but I drilled the lid of my fermenter for another grommet,
then epoxied a piece of tubing onto an 8 inch thermometer.
I think the idea is a good one, but I can't say anything good about those thermometers.

P1000037.JPG
 
I just use those cheap stick-on thermometers. They're accurate within a degree or two.

They'll tell me the temperature of the beer, but won't let me control that temp. So I'd have to guess how much cooler to set the freezer to keep the beer at the desired temp and and adjust it as fermentation cools down. Which I have done, but is less precise.
 
Suggested insulating material that would attach easily to the carboy? Any other ideas anyone?

I actually haven't done this yet, but I probably will for my next lager. I've been immersing my temperature probe into the beer to control the temperature, but I like the simplicity of just attaching it to the side of the carboy. There are other benefits, too, including a less complex cap for the carboy and a smaller swing in temperatures (I'm hoping, anyway).

So, I will probably rig some type of foam insulation around the probe, but if I'm feeling lazy I might just use some towels. I've also heard that bubble wrap works well.

-Steve
 
I've got a digital thermometer the kind with the chord. I was thinking about poking a hole in fermentor lid feeding the chord through then sealing it tight with some gasket maker. Can anybody see anything wrong with this? Aside from having to spend another $20 on a new thermometer that is. Not trying to hijack your thread just thought this idea might help.
 
I use a Stopper Thermowell, Like this one from BMW.

http://www.brewmasterswarehouse.com/products/Stopper-Thermowell-0102048

The ranco probe fits perfect.

+1

It does have a hole for a airlock. I've tested my digital ranco with the outside temperature strip and they match within a degree. I was surprised how accurate that little sticker was.... I love the thermowell. I use it in the summer to control a freezer, and in the winter to control a heat pad (with the ranco of course).
 
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