Fermentation Temperature

I'm brewing a Belgian Wit tonight and I'm not really sure what temperature I should set my temperature control on my chest freezer. I know fermentation will cause the wort to be warmer than the air temperature, so any help will be greatly appreciated. Thanks.

I would go low-mid 70's.

What yeast are you using? WLP400 or something similar? I'd probably set the temp to around 68 so it ferments around 72 or so.

You may know this already, but these yeast strains will produce different flavor profiles depending on the ferm temp. Lower temps will produce more clove and higher temps lend themselves to banana/gumball flavors.

Also, are you using a temp probe? I'd place that in a glass of water so you can get a more accurate idea of the wort temp. The air in the chest freezer does not conduct temp as well as water. I'd go with marubozo on the 4* differential, but add that after fermentation begins to taper off, the temperature differential will not be as great. The first 12 hours is going to be the most crucial.

HometownHoosier said:

I'd place that in a glass of water so you can get a more accurate idea of the wort temp.

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How would a glass of water be any closer to the beer temp? The beer would first have to heat the air, then the glass and water....

Tape the probe on the fermenter and insulate it from the air with bubblewrap or similar.

I would start at the low side of the recommended range and ramp it up slightly as the kraeusen falls.

I meant to write that its a better indicator of the freezer's actual temp.

The water is a better indicator of the actual temp inside the chest freezer due to water transferring heat differently than air. Also, when he opens the chest freezer to check on the yeasty beasty, the temperature of the water will not fluctuate as much as the temp of the air inside the chest freezer. This will help to keep the chest freezer from cycling on and reducing the temp more than necessary. The wort and the water glass will be closer in temp than that of the air, the fermenting wort, and the temp probe.

I'm more concerned with the temperature of the air surrounding my beer than the temperature of some random glass of water in said airmass. But moreover I care about the temperature of the beer.

If we take a refrigerator to be a closed system, an active fermentation inside it will ALWAYS be warmer than the air inside. By how much? Unknown. This is why one should never rely on the temp of the air in the fridge, much less another thermally damped mass, to gauge the temp of a ferment.

HometownHoosier said:

I meant to write that its a better indicator of the freezer's actual temp.

The water is a better indicator of the actual temp inside the chest freezer due to water transferring heat differently than air. Also, when he opens the chest freezer to check on the yeasty beasty, the temperature of the water will not fluctuate as much as the temp of the air inside the chest freezer. This will help to keep the chest freezer from cycling on and reducing the temp more than necessary. The wort and the water glass will be closer in temp than that of the air, the fermenting wort, and the temp probe.

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I have to agree with Hometown here, water retains temperature much better than air. Ever been for a swim on a warm winters day? Fermenting wort creates heat, exactly how much would be difficult to guess on a case by case basis but a glass of water is a good equaliser when taking temp readings, much better then air in an unenclosed place.

Uhm, no. The glass of water's temp tells you less about the beer temp than the air as long as the beer is fermenting.

Heat source.....cooling air......glass of water.

The heat source will always be warmer than the water.

944play said:

Uhm, no. The glass of water's temp tells you less about the beer temp than the air as long as the beer is fermenting.

Heat source.....cooling air......glass of water.

The heat source will always be warmer than the water.

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Yes that is true, however a glass of water will provide a better temp reading than the surrounding air as the temperature is more constant. If you can figure out how much of an increase in temperature fermentation causes then the glass of water will provide a more accurate base reading. In an enclosed environment however I see no reason why an air reading wouldnt provide the same accuracy for a base temp as water would.

My goal is not to control the temperature of a glass of water, so measuring the water is irrelevant. The airspace is more directly correlated with the beer temp.

I have no desire to guesstimate what a particular fermentation's rate will be and calculate some arbitrary compensation factor, I want to CONTROL THE EFFING TEMP of the BEER. Last thing I would want is another layer of damping and uncertainty.

Mostly, I would like to avoid the beer temperature falling before completion. Adding a damping factor almost guarantees it.

Pommy said:

Yes that is true, however a glass of water will provide a better temp reading than the surrounding air as the temperature is more constant. If you can figure out how much of an increase in temperature fermentation causes then the glass of water will provide a more accurate base reading. In an enclosed environment however I see no reason why an air reading wouldnt provide the same accuracy for a base temp as water would.

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If the question were which can provide a more consistent/stable temp reading inside the freezer, the glass of water idea would have merit. However, since our concern is all about controlling the temp of the fermenting beer, knowing the temp of a glass of water is not useful given the alternative.

Keep in mind that the alternative is not measuring the temp of the air (as you and HometownHoosier seemed to be suggesting). The alternative is to:

944play said:

Tape the probe on the fermenter and insulate it from the air with bubblewrap or similar.

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The key here is that your are insulating the probe from the ambient air. This allows you to measure the temperature of the fermenting wort itself. Not some isolated thermal mass. And the gallons of wort in the fermentor are actually a bigger thermal mass (i.e. more stable) than a glass of water, so the concern about cycling the freezer is even less of a concern.

944play said:

I'm more concerned with the temperature of the air surrounding my beer than the temperature of some random glass of water in said airmass. But moreover I care about the temperature of the beer.

If we take a refrigerator to be a closed system, an active fermentation inside it will ALWAYS be warmer than the air inside. By how much? Unknown. This is why one should never rely on the temp of the air in the fridge, much less another thermally damped mass, to gauge the temp of a ferment.

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I'm with this guy. Ambient temperature is not really what you are after - you want the beer temp. Unless you have a probe directly in the beer the best practice is to attach the probe to the side of the fermenter and then insulate it so that you aren't getting any ambient temps. Just my opinion. I tape the probe of my temp regulator to the bucket and let that control the temp of the fridge I use. As long as my fridge keeps the beer at a certain temp I don't care what the actual fridge temp is.

I think that one of the flaws in my reasoning is that I did not account for the evaporation of water in the glass cooling the water. A closed fermenter is not going to see the same evaporative effect.

My main idea with the glass of water was to measure a similar thermal mass and the ability of the cold air inside the freezer to transfer heat away from that mass. This is probably my second flaw. 16 ounces of water have a different thermal mass than 5 gallons of water.

In the big scheme, it only matters that we are cooling the fermenting beer. In this heat, anything is better than nothing. I like how this forum really pulls out the best techniques. Thanks for the discussion.

HometownHoosier said:

My main idea with the glass of water was to measure a similar thermal mass and the ability of the cold air inside the freezer to transfer heat away from that mass.

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Understandable, but the idea is to measure/control the beer, not the air. The key difference between beer and water is that the beer is producing heat during fermentation while the water is static. If you were trying to ferment at 65*, for example, the ambient might need to be 55* while the yeast are really cranking in order to keep your beer at the target temp. Once fermentation is over, the freezer could probably hold right at 65. If you were measuring water, the water would reflect the ambient and read a steady 65, whether or not your beer was 65, 70, etc. That's why we're advocating that you control your beer temp directly. I only care about the beer temp, nothing else in the system really matters.

In the big scheme, it only matters that we are cooling the fermenting beer. In this heat, anything is better than nothing. I like how this forum really pulls out the best techniques. Thanks for the discussion.

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+1.

944play said:

Tape the probe on the fermenter and insulate it from the air with bubblewrap or similar.

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This is what I do and it is common during the first few days of fermenting for the Fermentor to be at the setpoint, the wort inside about 1-2 degrees higher and the air temp to be 10-20 degrees cooler.