# How Much Heat Does Fermentation Generate



## drtomc (19/1/10)

Hi All,

I've been discussing building a peltier device based temperature control "fridge" for fermenting with a colleague, and the question came up as to how exothermic fermentation actually is. Obviously it varies, some ferments being quite gentle, and others extremely vigorous, but how many W/L are we looking at?

The reason for asking is of course to determine if a given peltier device will be able to remove the excess heat.

Anyone?

T.


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## Paul H (19/1/10)

Personally I have found variances of up to 7C however it changes depending on the specific stage of fermentation you are at.

Cheers

Paul


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## drtomc (19/1/10)

Paul H said:


> Personally I have found variances of up to 7C however it changes depending on the specific stage of fermentation you are at.



Is that in a fridge (i.e. an adiabatic chamber)? If that's the case, I guess we can compute the excess heat using the specific heat of wort (roughly the same as the specific heat of water, I guess) and the volume.
To work out the heat output in W we take into account the length of time it took to raise the temperature.

Let's try this....

20L wort,
7C
over 4 days....

specific heat of water = 4187 J/(Kg.K)

total energy released as heat = 20 * 4187 * 7 = 586180 J

over a 4 day ferment (345600s), that'd be about 1.7W.

That's assuming no losses or gains from the "fridge".

Thanks for reminding me of my 2nd year chemistry. 

T.


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## Adamt (19/1/10)

It'd be easier to estimate from the enthalpy change due to fermentation

There's too many variables to consider when looking at an observed temperature rise in a fridge.


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## raven19 (19/1/10)

It will certainly change for each and every beer.

Batch size, SG, FG, ambient temp, pitching rates, yeast health, aeration of wort, vessel shape... just to name a few of the variables I can think of.

An interesting but mighty difficult proposition to calculate it.


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## drtomc (19/1/10)

raven19 said:


> It will certainly change for each and every beer.
> 
> Batch size, SG, FG, ambient temp, pitching rates, yeast health, aeration of wort, vessel shape... just to name a few of the variables I can think of.
> 
> An interesting but mighty difficult proposition to calculate it.



Right, but I just want to work out how many watts I need to pump out of the insulated container to hold the temperature stable. The calculation above does that, and implicitly takes into account a host of factors. So long as I can bound from above so that I can maintain temperature *most* of the time, I'm happy. If a 20L fermentation goes up by 7C over a few days (1.7W), then given good insulation, a Peltier device capable of pumping 50W will probably be sufficient.  Of course, don't think too hard about the power consumption or your inner greenie will rebel.

T.


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## raven19 (19/1/10)

Fair enough. There is also the ramp up time taken for the yeast to get going, then peak ferment, then it slowly dissipates again.

I ignore my inner greenie when I ferment in the fridge with temp control, but balance that by no chilling my wort!  

You could make an assumption as you have, go with it and record the wort temp over time to track the progress. Then adjust as required for the next batch and so on.


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## komodo (19/1/10)

I have an inner greenie? :huh:


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## mfeighan (19/1/10)

haha peltier devices, reminds me of something i did very similar to http://www.grynx.com/projects/peltier-beer-cooler/
except mine was powered by pc power supply, a bit dangerous come to think of it


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## Adamt (19/1/10)

Just did some rudimentary thermochemistry calcs, assuming 60% actual attenuation, heat is dissipated into water (for heat capacity purposes), adiabatic conditions.

The fermentation of sugar in 1.040 wort will raise the temperature by about 9C.

Oh, and it will release about 750kJ.

So you were pretty close! (other heat would have gone to fermener, air in fridge, fridge lining, shelves, etc.)


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## drtomc (19/1/10)

Adamt said:


> Just did some rudimentary thermochemistry calcs, assuming 60% actual attenuation, heat is dissipated into water (for heat capacity purposes), adiabatic conditions.
> 
> The fermentation of sugar in 1.040 wort will raise the temperature by about 9C.
> 
> ...



Nice.  

If I end up building the thing, it'll have temperature/power data logged (hmmm, I think there's an micro controller out there with integrated bluetooth....), so I can see how much is generated. If.... I haven't wielded a soldering iron in anger for 25 years. Perhaps I can bribe a postgrad here with some homebrew - my desk is in an Electrical Engineering department after all....

T.


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## Adamt (19/1/10)

With fermenter cooling it's much less of a matter moving the heat away from the fermenter as it is getting the heat from out of the beer, and through the fermenter walls.


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## Phoney (19/1/10)

drtomc said:


> Is that in a fridge (i.e. an adiabatic chamber)?




:lol: :lol: :lol: 

That's it, from now im going to start calling my fridge the adiabatic chamber. Cant wait to see the look on people's faces...


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## drsmurto (19/1/10)

raven19 said:


> Fair enough. There is also the ramp up time taken for the yeast to get going, then peak ferment, then it slowly dissipates again.
> 
> I ignore my inner greenie when I ferment in the fridge with temp control, but balance that by no chilling my wort!
> 
> You could make an assumption as you have, go with it and record the wort temp over time to track the progress. Then adjust as required for the next batch and so on.



OT but chilling wort doesn't have to disagree with my (or your) inner greenie.


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## drtomc (19/1/10)

DrSmurto said:


> OT but chilling wort doesn't have to disagree with my (or your) inner greenie.



Indeed, but buying imported base malt does.  

T.


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## Adamt (19/1/10)

phoneyhuh said:


> :lol: :lol: :lol:
> 
> That's it, from now im going to start calling my fridge the adiabatic chamber. Cant wait to see the look on people's faces...



Your oven is also (practcally) an adiabatic chamber!


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## newguy (19/1/10)

I just brewed a 1.061 OG (I know, too high) schwarzbier Wednesday (double batch) and I have it locked in an insulated chamber. The first day was the worst, control wise. Once it hit low krausen, it was difficult to keep the temperature down. I have a very low tech method for that: freezer packs.

2 x (roughly) 1.5l each freezer packs every 12 hours worked to keep the temperature constant. Each pack entered the chamber @-19C and exited at ~8C. The specific heat of ice is 1938J/kgK and water is 4186J/kgK. So the packs absorbed 19C x 3kg x 1938J/kgK + 8C x 3kg x 4186J/kgK = 210,930J. That's over about 12 hours, so 210,930J/(12 x 60 x 60) = 4.88W. That's assuming of course that the heat generated is evenly distributed over that 12h timeframe, which it probably isn't. If you design your system with 5-6W of cooling power for a single 20l batch or 10-12W for a double (40l) batch, you should be fine.

Edit: fixed math.


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## seravitae (19/1/10)

you *did* account for the enthalpy of fusion, didn't you?? :unsure:


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## wessmith (19/1/10)

From Kunze: 587kJ = 0.16KwH per 1 kg of extract. Put another way and taking an average: 4500 kJ/100L

Wes


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## drtomc (19/1/10)

wessmith said:


> From Kunze: 587kJ = 0.16KwH per 1 kg of extract. Put another way and taking an average: 4500 kJ/100L
> 
> Wes



[sorry - number keys a busted on this keyboard]

times attenuation / time, I presume will give you W.

T.


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## growler (19/1/10)

All the above numbers may be correct, but only accounting for the exothermic yeast reaction is like working our the kw required to propel your car along a flat road at a steady speed. Add hills, traffic lights and a trailer full of sand on the back and youll need much more to get up to speed.

My fridge takes about 8 hrs to drop 50lt from ambient (28-30ish C) to 12C for a lager ferment.

Dont think a few peltiers would do it. 

growler


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## newguy (19/1/10)

sera said:


> you *did* account for the enthalpy of fusion, didn't you?? :unsure:



D'oh! No I didn't. Thermodynamics wasn't my forte. Add a couple of watts to my previous numbers and that should cover it.

But as someone else has pointed out, these calcs are only valid if your wort starts off at pitching temperature. A few watts' worth of cooling wouldn't be adequate to cool 20-30C wort down to 10C in the first place. Add a few more watts if your insulation isn't that great.


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## Nick JD (19/1/10)

My fridge set on "1" is between 17C and 20C. Set on "2.5" is 13C for lagers.

What the yeast gets up to behind that hot and steamy plastic is none of my godamn business. How rude.


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## samhighley (19/1/10)

drtomc said:


> I've been discussing building a peltier device based temperature control "fridge" for fermenting





drtomc said:


> [sorry - number keys a busted on this keyboard]



Perhaps the time would be better invested in fixing your keyboard?


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## drsmurto (20/1/10)

drtomc said:


> Indeed, but buying imported base malt does.
> 
> T.



Touche'

When I can buy Australian base malt that is as good as the imported stuff I'll be a happy hippy.


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