Heat generation during fermentation

Is there any way to calculate the difference in ambient temp and wort temp using OG and yeast pitched? Everything I have seen says about 5-10 degrees higher for actively fermenting wort. Is there any way to actually nail this down with a little math?

wdwalter said:

Is there any way to calculate the difference in ambient temp and wort temp using OG and yeast pitched? Everything I have seen says about 5-10 degrees higher for actively fermenting wort. Is there any way to actually nail this down with a little math?

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I don't believe so, There are too many variables involved. Basically the more active the fermentation the more the temp rises.

Ummmm, that's what thermometers are for, to completely take any guesswork out of it. In it's simplest form, you have the fermometer (stick on the outside of the fermentation vessel). At the top end of the scale you have thermwells with probes sent down them to give a temperature reading (with the opening of the thermowell blocked off to keep the temperature in it stable.

BTW, yeast is a living thing and will react/act differently in different brews. Even if you brew the same recipe you can have different temperature increases depending on other variables. I don't see how you could get all of them figured out, in such a way that a brewer wouldn't need to enter a dozen (or more) pieces of data.

Not to mention that it will depend on the conductivity (glass, plastic, stainless) of your fermentor.

Phunhog said:

Not to mention that it will depend on the conductivity (glass, plastic, stainless) of your fermentor.

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That's why I use a thermowell going into the middle of the ferementer, sealed at the opening, with a digital probe going down into it. The probe goes almost to the bottom, and has a display placed on a shelf nearby. That way I don't need to worry about ambient temps influencing the reading. I have all my fermenting caps set up that way.

And don't forget the temp difference will change every hour or day too, since activity changes. So a graph of temp difference versus time would look like a broad bell curve. You *might* be able to approximate the temp difference as a function of CO2 output for a given container type. But that probably doesn't help much.

What's the point of this exercise anyway?

SpeedYellow said:

And don't forget the temp difference will change every hour or day too, since activity changes. So a graph of temp difference versus time would look like a broad bell curve. You *might* be able to approximate the temp difference as a function of CO2 output for a given container type. But that probably doesn't help much.

What's the point of this exercise anyway?

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Point??

No, there is no way to calculate the projected temperature change using the variables you listed, other than simply, up. As others have pointed out you can monitor it.

5-10 degrees higher with air, 3-5 in cooler full of water up to beer level. General rule of thumb

My lagers don't like your rule of thumb. I usually see more like 3-5F with lagers. Seems to be a bit lower than my ales. YMMV.

Golddiggie said:

That's why I use a thermowell goting into the middle of the ferementer, sealed at the opening, with a digital probe going down into it. The probe goes almost to the bottom, and has a display placed on a shelf nearby. That way I don't need to worry about ambient temps influencing the reading. I have all my fermenting caps set up that way.

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Hmmmm....why do you place it at the bottom of your fermenter if heat rises? It would seem that you would want to place it near the top of the wort. Of course if the theory is that all the wort is essentially the same temperature then it doesn't really matter where you place your probe. You could even place it on the outside of the fermenter as long as you insulated it from the ambient temperature.

The probe stops before the bottom of the fermenting vessel. About 6-8" from the bottom in fact. So the sensor might be in the bottom 1/3 of the vessel. The way the thermowell works, it's getting the temperature from all of what it's in contact with. With the plug in the top, it stabilizes that reading for me.

Besides, as long as I'm within a degree F, I'm happy. At least I know the ambient air temp is not influencing my temperature readings.

SpeedYellow said:

My lagers don't like your rule of thumb. I usually see more like 3-5F with lagers. Seems to be a bit lower than my ales. YMMV.

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Ill change it to a theory of thumb lol I've never done a lager in a cooler lol

Golddiggie said:

That's why I use a thermowell going into the middle of the ferementer, sealed at the opening, with a digital probe going down into it. The probe goes almost to the bottom, and has a display placed on a shelf nearby. That way I don't need to worry about ambient temps influencing the reading. I have all my fermenting caps set up that way.

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so based on your measurements - are you in the 3-5 camp or the 5-10 camp?

brycelarson said:

so based on your measurements - are you in the 3-5 camp or the 5-10 camp?

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Hey now, I didn't mean to imply there are 2 mutually-exclusive camps. I only meant there seems to be a lager range and an ale range. I've seen 3-5F with lagers but 5-8F with ales.

I use a swamp cooler (igloo cube cooler) and have done two experiments measuring the swamp cooler water and then sticking the thermometer (sanitized) down into the fermenting wort. I've done this for 2 brews both about 1.055 and measured 3 days in a row during active fermentation. So, I had 3 data points for each brew, 6 total. Every time their was no material difference between the temp of the cooler water or the center fermentation column. Conclusions: There is enough thermal mass in my cooler water to keep the ferm temps within a degree of the swamp cooler water temp. So now I am pretty comfortable taking the swamp temp and assuming my ferm temp is roughly the same.

brycelarson said:

so based on your measurements - are you in the 3-5 camp or the 5-10 camp?

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It goes up what it goes up. Normally it ferments within the range the yeast likes, so I don't worry about it. I typically aim for it to start in the low end of that range, so it won't go above the middle of the range.

Right now, I have a big barleywine fermenting in the basement. The ambient temp in there was 52 this morning (right where the vessel is sitting). Inside temp was 58F. Previously, it was about 4F above ambient. I wrapped it with some insulation (single layer) last night and added some heat for 2 hours. It lost only a single degree overnight. I've added another layer today, after giving it another 2 hour shot of warmth. It will be interesting to see how well it retains it's temperature today.

IME, a lot really depends on the wort temperature either when you pitch, or what it reaches before the yeast goes full active. Use the same yeast strain for your batches and you'll learn how it reacts under different conditions.

SpeedYellow said:

Hey now, I didn't mean to imply there are 2 mutually-exclusive camps. I only meant there seems to be a lager range and an ale range. I've seen 3-5F with lagers but 5-8F with ales.

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No insult intended.

I'm a data guy - the more the better. I don't have a thermowell - so just looking for reports from other people to use as a base line. If I know that an active ferment will be 5+ and a moderate or slow will be closer to 3-5 - that's helpful information.

RmikeVT said:

I use a swamp cooler (igloo cube cooler) and have done two experiments measuring the swamp cooler water and then sticking the thermometer (sanitized) down into the fermenting wort. I've done this for 2 brews both about 1.055 and measured 3 days in a row during active fermentation. So, I had 3 data points for each brew, 6 total. Every time their was no material difference between the temp of the cooler water or the center fermentation column. Conclusions: There is enough thermal mass in my cooler water to keep the ferm temps within a degree of the swamp cooler water temp. So now I am pretty comfortable taking the swamp temp and assuming my ferm temp is roughly the same.

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That is why I think fermenting in a temp controlled water bath is much better. Most people do the temp controlled fridge because it is easier but water is much better insulator than air.

I use the fridge. I tape the probe from the temperature controller onto the bucket. In a sense, I guess I'm letting the yeast operate the fridge for a while. It would be more accurate to have the probe in the middle of the wort, but then I would have to wrap my probe.

And no one wants that.

xkred27 said:

I use the fridge. I tape the probe from the temperature controller onto the bucket. In a sense, I guess I'm letting the yeast operate the fridge for a while. It would be more accurate to have the probe in the middle of the wort, but then I would have to wrap my probe.

And no one wants that.

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I sheath mine in stainless steel. :rockin:

1 W/(m.K) = 1 W/(m.oC) = 0.85984 kcal/(hr.m.oC) = 0.5779 Btu/(ft.hr.oF)

Alcohol 0.17

Air, atmosphere (gas) 0.024

Glass 1.05
Pyrex glass 1.005

Ice (0oC, 32oF) 2.18
Snow (temp < 0oC) 0.05 - 0.25
Water 0.58

Aluminum 205
Copper 401
Iron, cast 55
Stainless Steel 16

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Just for fun, let me throw some numbers for thermal conductivity into the mix.

I don’t know about air, but for water the inside vs outside temp is a few tenths of a degree F. That’s for a water bath with frozen bottles cooling a glass fermentor.

If you figure the difference in conductivity is x24, then 8-10 F corresponds to .33 -.40 in water, compared to air.