Fermentation chamber

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bellybuster
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Re: Fermentation chamber

Post #11 by bellybuster » 2 years ago

I now run a STC1000+ which al;so has an ambient temp probe. Being able to see and compare really brings things to light.
BottomsUp
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Re: Fermentation chamber

Post #12 by BottomsUp » 2 years ago

ruf1 wrote:
bellybuster wrote:+1 agreed, when i was measuring ambient temp i checked the temp of the beer compared to ambient and the beer was 6 degrees above the ambient temp, thats when i started to measure beer temp instead, i can check beer temp and probe-water temp within 1 degree of each other. :D

As I mentioned, it all depends on where your probe is placed. In your case, your probe was likely too low, where it is cooler.
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Re: Fermentation chamber

Post #13 by BottomsUp » 2 years ago

bellybuster wrote:the above sounds logical but in actual service it just doesn't work that way. Measuring ambient as your temp source causes much cycling.

I respectfully totally disagree. I have done much experimentation and the only way to minimize the beer temperature from fluctuating is to measure the ambient temperature. The key is where the probe is positioned, as there is a significant difference in temperature between the bottom of the chamber and the top. The temperature of my beer is very constant and is usually right on the temperature.
kombat
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Re: Fermentation chamber

Post #14 by kombat » 2 years ago

Putting the probe in a jar of water is the worst possible solution. The thermowell is the ideal solution.

Here's why: Think about what happens during fermentation. You've got your fermenter sitting in the fridge, and the beer is at exactly the right temperature. The yeast start working, producing heat. The beer warms up a little bit. If you had the probe inside a thermowell, then the temperature controller would know immediately, and could turn on the fridge to keep the temperature where it's supposed to be.

But your probe isn't in a thermowell. It's in a jar of water, which hasn't changed temperature (because there are no yeast in it producing heat). So the beer warms up. This warms up the surrounding air in the fermentation chamber. If your temperature probe were dangling loose, this is the point at which it would notice an increase in temperature, and could turn on the fridge to cool things back down.

But your probe isn't dangling loose. It's still in that jar of water. Now that the surrounding air has started warming up, the water in the jar finally also starts warming up. Meanwhile, the temperature of your beer is spiking, because the yeast are getting more and more excited, and the temperature controller still hasn't yet turned on the fridge to cool things down.

Finally, the temperature of the water in the jar increases by enough to trigger the temperature controller to activate the fridge. But by now, who knows how warm your beer has gotten in the meantime.

Now, a similar problem occurs while cooling down. The temperature controller notices that your jar of water has warmed up a little, so it turns on the fridge. The fridge cools the air down, which slowly cools down the water in your jar. It cools the beer down a little bit too, but not as much, since it a) has more thermal mass, and b) has active yeast in it producing heat. Before too long, the water in the jar has cooled back down to the target temperature, so the temperature controller kills the power to the fridge. But the beer is still too warm. The air inside the fridge will be considerably cooler than the water in the jar, so the water in the jar might continue to cool for a while, before bottoming out and starting to warm up again. During this whole time, the beer is still above the target temperature, and getting hotter again.

As you can see, this is a terrible solution. Best idea, probe in thermowell in beer, second-best idea, tape probe to the outside of the fermenter and cover it with some sort of insulator (foam, bubble wrap, whatever), third best is to just let the probe dangle freely in the air. But immersing it in a separate liquid is the worst possible solution.
BottomsUp
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Re: Fermentation chamber

Post #15 by BottomsUp » 2 years ago

Again, putting the probe directly in the beer is NOT the best solution.

Let me try to explain again. Imagine that your beer is at the right temperature. The fridge/freezer does not turn on. The beer starts to very slowly warm up (liquids take much longer to change termperature than the air). Finally it triggers the fridge/freezer to turn on. The temperature in the chamber continues to cool down lower and lower. Since it takes very long for all the beer to cool down, the chamber gets colder and colder, and the fridge/freezer stays on for a long time. Finally the beer cools down to below the proper temperature when the freezer/fridge turns off. Meanwhile, the chamber is extremly cold - MUCH colder than the temperature of the beer. So the air continues to cool the beer down lower and lower. Eventually the beer reaches an equilibrium with the air temperature, which is lower than the temperature you want the beer to be at. Because of the volume of beer, the air temperature stays relatively cool for a long time, equilizing with the beer temperature as best as it can.

Eventually, over a long period of time, the beer begins to warm up and the fridge/freezer again turns on.

What has happened here is that the beer has deviated significantly from the temperature you want, so there is a significant fluctuation of the beer temperature (the fluctuation goes lower than you want).

Now imagine the beer at the proper temperature and the probe dangling in the air about a third of the way up from the bottom of the chamber. The volume of beer at that temperature will keep the air in the chamber more or less at that temperature (equilization) until the beer and air begin to warm up. Once it's a few degrees above the ideal beer temperature, this triggers the fridge/freezer to turn on. The probe is measuring the air temperature, not the beer, so it doesn't take long for the air temperature to cool to say a few degrees below the temperature of the beer that you want (you set the range for your temperature controller). Now the air temperature and the beer begin to equilize, and very slowly, the beer and air chamber temperature drops to where it turns on again. Thus in this scenario, the beer fluctuates a very small amount (maybe a couple of degrees above and below the ideal beer temperature), providing a good average. Also, the air temperature in the chamber also fluctuates a much smaller amount than in the scenario where the probe is directly measuring the beer.

If you don't believe me, try both approaches and measure the temperature of the beer. You will find a much greater variation from the ideal temperature when placing the probe directly in the beer (or against its side) than if you place the probe in the air. Just remember to adjust the position of the probe so that it's approximately half way up the carboy, since the bottom of the chamber will be cooler than the top. You want to average out the reading.
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Re: Fermentation chamber

Post #16 by kombat » 2 years ago

BottomsUp wrote:Eventually the beer reaches an equilibrium with the air temperature, which is lower than the temperature you want the beer to be at.


I can understand why you'd think that, but in practice, it's not actually an issue. I have my STC-1000's tolerance set as low as it will go (0.3° C), and it rarely "overcools," needing to trigger the heating circuit. The way you describe it makes it sound like using a thermowell would cause the system to constantly cycle between heading and cooling commands, and that's simply not what happens.

Yes, when the beer has cooled to the right temperature, the surrounding air in the freezer is significantly colder. But the freezer is not a perfect insulator, and indeed, the lid has a gap in it where the probe cord and heating belt power cord slip in. As you noted, liquid has a much higher thermal mass than air, so the air will warm back up much faster than the beer cools down.

Finally, even if what you wrote were correct, I would much rather have my beer fermenting a fraction of a degree cooler than I expected than several degrees warmer (as would be the case if the probe were immersed in a separate vessel of liquid inside the fermentation chamber). Fermenting too warm, in my experience, produces vastly more unpleasant off-flavours than fermenting slightly cool.
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bellybuster
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Re: Fermentation chamber

Post #17 by bellybuster » 2 years ago

with my probe attached to the side of the fermenter with some insulating foam I seldom have more than a degree of swing inside the fermenter. If I put it in warm it will take it a couple degrees low and then it will equalize.
I've tried every which way and controlling by beer temp results in the most stable temp by a long shot
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Re: Fermentation chamber

Post #18 by oro » 2 years ago

bellybuster wrote:with my probe attached to the side of the fermenter with some insulating foam I seldom have more than a degree of swing inside the fermenter. If I put it in warm it will take it a couple degrees low and then it will equalize.
I've tried every which way and controlling by beer temp results in the most stable temp by a long shot



what I do too, easy as can be and works great
Beer has food value, food has no beer value...
BottomsUp
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Re: Fermentation chamber

Post #19 by BottomsUp » 2 years ago

I've said my say. Theory is one thing - practice is another. Give both ways a try, measure carefully and see what you come up with.
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bellybuster
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Re: Fermentation chamber

Post #20 by bellybuster » 2 years ago

check out the Brewpi web page. There are many graphs available to prove that measuring beer temp is solidly the far superior way. Even better is to read and compare beer temp and ambient (STC1000+)
easy way to look at it is by thinking jacketed fermenters, they measure beer temp, not coolant temp. The coolant temp is irrelevant as long as it is lower (cooling) or higher (heating) than the beer it is meant to cool or heat

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