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Home Brew Forums > Home Brewing Beer > Brew Science > Temperature difference in and out of a fermenter?
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Old 01-03-2013, 06:01 AM   #1
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Default Temperature difference in and out of a fermenter?

Fermentation is known to produce heat and the actual temperature of the fermenting wort is therefore higher than its surroundings. I have a thermometer in my fermenting fridge but I can't help but wonder how reliable is the reading I get. I don't have a thermometer in the fermenter or wort itself.

Did anyone experiment with taking temperature of the fermenting wort vis-a-vis its surroundings?

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Old 01-03-2013, 06:12 AM   #2
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The ambient air is an unreliable correlate to the temperature of fermenting wort, and there's really no simple way around that. If you tape the thermometer to the side of the vessel, though, you'll get a very accurate result, especially if you slap on a bit of insulation.

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Old 01-04-2013, 01:01 AM   #3
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Air is a terrible conductor of heat and there will be a difference between the air temperature and the fermentation temperature. Water, however, is a much better conductor. A water bath with stay withing 1 degree of the fermentation temperature.

See here for details:
http://woodlandbrew.blogspot.com/201...e-control.html

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Old 01-04-2013, 01:34 AM   #4
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Comparatively speaking, water is a better conductor though it is still considered poor no? So even if we take the temperature of the walls of the fermenter, it is probably not ideal even though it is a vast improvement over taking the ambient temperature, I guess?

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Old 01-04-2013, 01:40 AM   #5
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Because temperature moves very slowly in fermentation the water temp and wall temp stay within a degree of the temperature in the middle of the 5 gallon pail.

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Old 01-04-2013, 01:49 AM   #6
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Quote:
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Comparatively speaking, water is a better conductor though it is still considered poor no? So even if we take the temperature of the walls of the fermenter, it is probably not ideal even though it is a vast improvement over taking the ambient temperature, I guess?
Water is a good conductor of heat, especially when it is being agitated by continuous CO2 off-gassing.

I had thermowells installed in all of my fermentors, but I don't even use them anymore because insulating a probe against the side gets me within half a degree every time. If you're looking for more precision than that, you're going to need a number of different sensors situated at different points in the mass.
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Old 01-04-2013, 01:56 AM   #7
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Ahhh! right there! Forgot about the CO2 agitation. I do have a stick on thermometer on the fermenter but I never learnt how to use that because the sticker lits up on a range of temperature and I never know how to interpret that.

This is the exact one I am using:

http://www.homebrew.com.sg/homebrew-...7794&id=836752

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Old 01-04-2013, 02:53 PM   #8
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I have these on my carboys and they work fairly well. look for the number that looks the brightest. You can also add warm (~70F) water to the carboy, let it stand and test the water temp with a thermometer. When you compare this to the stick on you get an idea how well it reads the temp in the fermenter.

Make sure to use water that is slightly warmer or colder than ambient since the concern of not being able to read the internal temp with the stick-on thermometers is when there is a temperature difference.

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Old 01-04-2013, 04:38 PM   #9
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I have a five gallon carboy in a tub filled with five gallons of water. I control the water temp and measure the beer temp with a thermowell. With a well controlled fermentation, the water temp difference is usually .3C. It will peak at .5 or .6C before gradually fading to zero. So I agree with WoodlandBrew, .5 -1.0F in water.

I don’t know what it would be in air.

Another wrinkle is that before the fermentation stirs things up, there is significant temperature stratification. I just took a batch out of the refrigerator and poured it into the carboy. After about an hour, I checked it with an IR thermometer, 14C at the bottom, 15C at the top. That’s almost 2F.

BTW, those stick-on thermometers fail when they get wet.

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Old 01-04-2013, 04:42 PM   #10
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ahhh that's gg to be problematic because i have constant condensations on my fermenter walls. it's hot and humid here and condensation is common in the fridge.

Damn.

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