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Old 03-04-2013, 10:53 PM   #1
BoomerHarley
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Default thermowell ruining my beer?

I brew in a 14.5 gallon conical inside a stand up freezer. Recently I put a thermowell on it and the probe reads from the center of the fermenting beer.

However, the last two batches (since the change) have both ended up not fermenting out and being very sweet (1.020 or so). Watching a digital temp probe I have inside the freezer I notice that now the temps range from 70 or so down to 34 degrees and I think I may be causing more of a problem than anything.

My assumption is that it takes so long for the thermowell to register a change in heat, that I am practically freezing the wort and yeast near the edges. Previous to the change, my fridge pretty much went on for a few minutes to drop the temp at the ambient probe, then turned off (vice versa for heat). Now it cycles very cold and was very hot but I replaced the room heater (cycled at 112-34 degrees) to an aquarium bukb (cycles from 75-34).

Any thoughts? At this point, I think the thermowell is not helping.

P.S. I searched and found 134375389339292 thread on thermowells, none of which seemed to address this issue.

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Old 03-05-2013, 01:15 AM   #2
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It's tricky. In an ideal situation, you do want to control the temp of the beer. If there's no fermentation happening, you will have a more steady temperature of the beer by controlling the air temp, or at least a test-tube of fluid in the fridge. You do want to control based off the temp of the beer to account for the exothermic fermentation. If I'm really on it, I control based off the beer temp during fermentation, and switch to air temps as its winding down. During the active fermentation, there will be plenty of convection to mix everything. You won't have frozen beer on the wall and 62degF beer around the thermowell.

More to your question, there's going to be a much greater variance in temperature from top-to-bottom than side-to-centre. This is when there is no fermentation to mix things up. I have a thermowell on my stainless fermenter, but I don't use it anymore. I did several experiments, and found that a taped-on probe, covered with a couple layers of unfolded pipe insulation, was reading exactly what the thermowell was. Not only that, but the taped-on probes responded faster than the thermowell probe. This was because my probe wasn't in mechanical contact with the tip of the thermowell. If it was, it would probably respond as fast as the taped-on probes. I did find a significant (>10degF) variance from top to bottom when there was no active fermentation. This was when a cooling or heating cycle would start. I had been using an immersion coil for chilling and a 400w silicone heat mat on the side for heating. I found that the temperature of the beer was much more even top-to-bottom when I heat/chill the air in a ferm cabinet. I have a small computer fan circulating constantly.

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Old 03-05-2013, 01:32 AM   #3
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Thermowell, especially larger ones, will take a significant amount of time to react to temperature changes compared to other probes. But depending on the rate that you are changing the temperature in the fermenter, 1-2 degrees every couple of minutes, it should be able to respond that quickly. When you say that the temps are ranging from 70 or so down to 34, are you getting this information from tracking the temp from the probe or from another temp guage or thermometer on the side? My thought being that if it was coming from the probe then you should easily be able to see how fast it is reacting vs another temp guage. If you cannot see any temp readout I would try to check the voltage coming from the thermowell to make sure its giving the correct outputs to the controller from a known temperature of liquid, not sure how to do this, though, but i'm sure the manufacturer has some documentation on what voltages/amps it should be putting out, like if it was a 4-24mA signal.

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Old 03-05-2013, 01:37 AM   #4
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St Marcos, thanks. I think the computer fan may be in order.

tsl346, I have a digital thermometer with a remote that I can set in a fridge and read from my desk. I have it in the door of the fridge so it is getting ambient temp. The problem is when the freezer comes on, it comes on strong and the air temp goers way down, but it takes a while for 10+ gallons of beer to catch up.

I think I'll probably do the tape with insulation thing.

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Old 03-05-2013, 06:43 AM   #5
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The taped on probe likely won't help much with the air temp swings in the chamber... compared to the tw that is. What it will allow you to do is move it around and get an idea how much the temp is different from top to bottom. The comp. fan will help with this. Look for a fan with nearly the wimpiest cfm you can find... you don't want to be dumping too many watts in the chamber to compete with the chiller. I think mine was 12-15cfm.

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Old 03-05-2013, 12:52 PM   #6
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Don't worry about the temp swings of the ambient air in the freezer. There is very little thermal mass in the air compared to the beer. As others have said, during fermentation there will be plenty of current in the beer to keep it mixed up and prevent a freezing layer from forming on the outside.

The insulated probe taped to the side of the ferm vessel is just a substitute for a thermowell. It is kinda like a cheap, easy, sanitary, DIY thermowell.

Big conicals at "real breweries" are controlled exactly like you are doing. They have a thermowell and they cycle very very cold glycol through the jacket. You are replacing the glycol with really cold air.

The best thing you can do is stop using your digital thermometer.

Cum hoc non propter hoc. Now we just need to figure out what has caused your last two beers to finish high...

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Old 03-05-2013, 01:39 PM   #7
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Quote:
Originally Posted by Huff360 View Post
Don't worry about the temp swings of the ambient air in the freezer. There is very little thermal mass in the air compared to the beer. As others have said, during fermentation there will be plenty of current in the beer to keep it mixed up and prevent a freezing layer from forming on the outside.

The insulated probe taped to the side of the ferm vessel is just a substitute for a thermowell. It is kinda like a cheap, easy, sanitary, DIY thermowell.

Big conicals at "real breweries" are controlled exactly like you are doing. They have a thermowell and they cycle very very cold glycol through the jacket. You are replacing the glycol with really cold air.

The best thing you can do is stop using your digital thermometer.

Cum hoc non propter hoc. Now we just need to figure out what has caused your last two beers to finish high...

Interesting. Well in all honesty, the Kolsch hasn't really finished, but it's been ten days since I started and I would think it would be below 1.020. However, it is still actively fermenting so I'll give it some time.
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Old 03-05-2013, 01:56 PM   #8
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Take my un-qualified opinion for what it's worth, but I feel like you should only be measuring the temperature of the liquid inside the fermenter if you're directly cooling (or heating) the liquid. I think that regardless of currents in the beer mixing things around, the extreme range of temperatures you're monitoring in your fridge can't be good for the beer. Think about what initially qualified as temperature control in brewing... a cool room with consistent air temps.

One poster mentioned big breweries using glycol in a jacket, but that jacket is right on the surface of the fermenter, and is likely insulated so that cooling goes directly in to the liquid. They also may (likely) have more sophisticated (read: PID) temperature control mechanisms so as not to overshoot (which you can't do with a fridge compressor).

I think you're initial instinct is correct. I personally just regulate the environment in ferment in, not the contents of the liquid and all my tests so far show that my fermenter seems to be within about 1 degree of the ambient temperature. In fact, it's only ever off by 1 degree when fermentation is going full bore and extra heat is being produced, and is exactly matching when fermentation ramps down.

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Old 03-05-2013, 02:42 PM   #9
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Follow up:

Check out this post: http://www.homebrewtalk.com/f11/immersion-chillers-395062/#post4971588

I asked that poster to tell me if his controller is connected to air or liquid probes and I don't have an answer yet, but this person is monitoring temperatures inside their fermenter and inside the fridge.

The thing to note here is that only a 5 or 6 degree swing in air temperature is maintaining a liquid temperature within about 0.3 degrees, so I'd be willing to bet that the OP's air temperature swing of 35 degrees is drastically over-shooting how much cooling is needed to get the liquid where it should be, and that the cause of this over-shoot is how slow the liquid reacts to changes in air temperature.

That could just be because of how much liquid you're fermenting... I'm not sure, and I'm still keen to find out where the poster of the graph controls their temps from.

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Old 03-05-2013, 04:24 PM   #10
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Here's a good way to think about it.

Remove conical from freezer. Plug it in. Let it run a solid week so it gets good and freezing inside. Fill your conical with room temp water. Unplug the freezer. Set conical inside.

How much do you expect the temp of the water to change?

The temp of the inside of the freezer has very little thermal mass compared to the wort. If you sample air temp, your freezer will cycle on and off a lot. It's lots of short bursts of very little heat removal. The wort transfers heat into the air causing it to warm. The freezer then turns on remove the heat from the air, then turns off. The wort passes heat to the air, cycle on, repeat.

Moving the temp control into the thermowell causes the cycles to be MUCH longer. Yes, the ambient temp will get to freezing and stay there for a while. It takes a pretty long time for the wort to transfer it's heat to the air, then the freezer to remove that heat.

It won't result in frozen wort against the wall of the conical and hot wort in the middle. Even when it is not fermenting.

I'm going to bum a chart from a guy in my local club - Here he shows a thermowell vs the insulated probe taped to the side of the carboy. It's no different.

t197.jpg

The control in this setup was a dangling in ambient air probe, an old analog johnson.

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