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?

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.

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/2012/12/fermentation-temperature-control.html

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?

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.

hairy said:

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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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.

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-store#!/~/product/category=277794&id=836752

hairy said:

http://www.homebrew.com.sg/homebrew-store#!/~/product/category=277794&id=836752

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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.

Kai

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.

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.

I posted some graphs I did using various methods of chilling. Water baths are very effective, and during active fermentation there is very little difference.
Link to some charts here on HBT

In air, you can have quite wide temperature swings with little impact to the fermentor, one of the graphs shows that. In a water bath, you need to control the bath temperature much more carefully. If you are actually holding your air temp at a fairly constant temp, then your fermentor temperature is within that band.

What I have seen so far is it takes about 10 minutes for the temp at the side to reach the center in perfectly still wort. With air temp relatively constant, the core temp stays relatively constant. I can keep mine within half a degree in water.

I'm currently doing a test with a new chiller with very little dead air space (converted barrel cooler). Currently trying to see how fast it will pull down from 70 to lager temps in the 40's. Averaging 4F/hour so far. After it stabilizes, I can post a chart of core temp vs top and bottom of cooler temps. Kind of curious how it will turn out since I've done everything in water with a chiller to date.

hairy said:

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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Yeah, I lived there for two years, I remember everything feeling wet. Hoping to move back to SEA soon.

You might try getting a huge box of desiccant. I have one of these, and it keeps my fridge bone dry even in our humid summers here in Pennsylvania. I open and close mine a lot, since I also keep bottles in there. Bake it in the oven for a few hours to dry it out... of course, running the oven for a few hours over there isn't great either.

Here is a test I just completed with 5gal in a freezer. Even though there are two separate graphs the second is a continuation of the first with just a few minutes missing.

The sloped trace is actually two traces, an immersion thermocouple and fine wire surface thermocouple that was covered with three layers of Reflectix insulation. Typ <1F difference between the two. There was no fermentation, only plain water.

The oscillating trace is the freezer cycling around a 50F setpoint with 5F programmed hysteresis. Total duration to get from 71F to 50F was about 33 hours.

Here is my 5 gallon pull down from 70 to current. I think it will plateau at 36 using the cooler's built in thermostat. I can't go lower than that without bypassing it or finding a course adjustment. 70 to 50 in 5.5 hours.

If it settles at 36, the maximum difference on either side is 2-3 F. Your core temp is effectively the average of your min/max. The wider the delta the more fluctuation you'll see in the beer. The same is true in liquid, but small changes are more evident. If you could theoretically keep a fridge at a constant temp, your beer would reflect that.


I'm not sure why adding the larger fan caused the temps to swap between top and bottom.

This is the cooler I'm using for this. $30 Craig's List find.

I wonder how much hysteresis in the freezer air temp. it would take to see an oscillation in the temp of 5 gallons of beer?

whoaru99 said:

I wonder how much hysteresis in the freezer air temp. it would take to see an oscillation in the temp of 5 gallons of beer?

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Well, I've got nothing better to do with it, and the carboy using the controller is about to be kegged, so I'll set it at 60 +/- 4 and see what happens. I'll measure core temp, side of carboy, and temp at location of controller probe, and see what happens. Post back in a day or so as it stabilizes.

My stick on thermometers are almost always wet with condensation and they work fine. They are a good indicator of internal carboy temp.

Since you are fermenting in a fridge, I doubt there is much difference in the temps, maybe a degree or two. I'm assuming though that this is a commercial fridge, and equipped with a fan of some sorts. Air circulation is important, whether fermenting in a chamber or out in a room. I really speeds up heat transfer. When I built my custom chamber, after one brew, I realized that I needed a fan inside to keep the air circulating. It made a big difference in stabilizing the temperature and helped to prevent overshooting my target temp.

Here is some long term temperature data. The question was asked: How much variation leads to noticeable impacts in the fermentor. Answer: It takes quite a lot.

A bit about the setup. The chiller is pictured above. Wit ha carboy inside, there is very little airspace around it.
The air temp probe and the temp controller probe are tied together and hanging in in the middle of the air space, halfway up the side of the carboy. There is a computer fan circulating air.
The probe on the side of the carboy is embedded inside a chunk of high density foam insulation. I cut a channel and strap it firmly to the side so it's insulated and makes good contact. The probe is fully enclosed to minimize external influence as much as possible.

All probes apply correction factors after having been calibrated against my chosen reference thermometer.


Four items are shown here:

1. A messy ramp to get to around 58F. You can swing the air temp all over the map, and have very little impact. That much water has a strong influence on the ambient temperature once you seal it back up. Lots of capacity.
2. Set point of 58, with a hysteresis of 4, pretty much keeps it right at 58. While you can see a wave trend, it's essentially noise differences around 58F.
3. Set point of 56 with a hysteresis of 6... you would expect to stay around 58, but it rises above 60. This does make sense though. The air is very easy to cool, and the fridge air temp drops to the set point very quickly, then there is a bit of carry over since the walls are so cold. The temperature rise starts off very quickly, but then the rate falls dramatically right around the carboy temp. Since the rise is slow, and the hysteresis is two degrees higher, it does allow the carboy to ultimately rise in temp.
4. Lastly, the same 58 set point and 6 degree hysteresis, but I moved the probe from the core of the carboy to the point on the inside exactly opposite the probe on the outside. This shows the difference in temperature when measuring on the outside vs. the inside. Very clearly, there is an impact to the apparent temp due to the amount of glass exposed to the air. So, if you attach your temperature controller probe to the outside, you will get very different results, and it will be influenced by air temp, not beer temp to a point. Does it matter... you decide. We're talking 1 degree differences here.