does fermentation itself generate heat

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I started my first ever homebrew yesterday.  I put the brewer in the fridge
(turned off) at 24 C with an immersible heater nominally calibrated for 22
C.  When I go to check on it the next morning it is up around 24-26
(according to the strip heater).  The ambient temperature was nominally down
to 15 last night.  I am worried that I might over cook it.

I guess there could be various reasons for this.
    o the calibration on the heater is off.
    o the fermentation itself gives off heat.
    o the air inside the fridge warms up to the brew temperature which makes
the strip heater give a higher reading.
    o ????

What is the ideal temperature range (I used a Coopers Real Ale kit).

Any tips would be appreciated.



Re: does fermentation itself generate heat
Most ales ferment at room temp or 68-72F, if you are making a lager then
temp plays more of a role as it needs to be fermented cold and aged colder
using a lager yeast. for your particular kit your temp may be off but you
need to know the range for your yeast.

"sozman" <pauls> wrote in message
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Re: does fermentation itself generate heat
Yes fermentation does generate heat,

Kasper
Denmark
"sozman" <pauls> skrev i en meddelelse
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Re: does fermentation itself generate heat
Kasper,

Thanks - do you know if this is this significant enough to raise the wort
temperature by a couple of degrees in an insulated cabinet?

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Re: does fermentation itself generate heat

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Yep I have had a temp raise of 3-4 degrees C in an open room..

Cheers
Kasper
Denmark



Re: does fermentation itself generate heat
Warning: Geek alert.

Yeah, I believe it should give off heat.

Make the incredibly simplifying assumption (which I hope at least balances):

Glucose (C6H12O6) + Happy Yeast ---> 2 CO2 + 2 CH3CH2OH

Heat of formation of glucose: -1273 kJ/mol (A)
Heat of formation of CO2 (gas): -393 kJ/mol (B)
Heat of formation of ethanol (l): -277 kJ/mol (C)

Thus:

Total enthalpy = 2*B + 2*C - A
Total enthalply change = -67 kJ/mol which mean it gives off heat

Of course, this is incredibly simplistic as wort has different sugars
and the actual reaction is very complex. But since the net effect is
busting up some carbon bonds, it should be exothermic.

I leave it to the motivated student to use delta G and delta S to prove
it's spontaneous (or not)....;^)

But how much would it raise the temp? Hmmm....let's make the incredibly
simple assumption that all heat generated stays in the beer (ie,
perfectly insulated container) and use the specific heat capacity of
water (ignore ethanol's cp). Also assume that all s.g. above 1 is due
entirely to fermentable sugars, and that we have 100% attenuation. Use a
60 GU beer:

5 gallon batch * 0.060 g/ml (glucose contribution) * 3785 mLs/gallon *
1/180 g/mol = 6.3 mol glucose

6.3 mol * 67 kJ/mol * 1000 J/kJ * (1/4.18 J/g/K) * (1/18925 g) (mass of
5 gallons) = 5.33 K or 5.33 C which is about a 9.6 F increase.

Ethanol's cp is about 50% higher than water if I'm not mistaken, which
would mean the actual temperature increase would be lower (though
probably not by much). It'd also be lower due to unfermentables and less
than 100% attenuation.

Anybody wanna check my math or correct any misconceptions on my part?

sozman wrote:
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Re: does fermentation itself generate heat
Thanks Christian and Kasper.

So for practical purposes does this mean I should pitch my yeast when the
brew is well below the recommended top temperature for that yeast so that
the natural temperature rise doesn't "cook" it?

BTW my temperature has stabilised to 22C for over 24 hours now so at least
my heater calibration is ok, bubbling is very slow now.

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Re: does fermentation itself generate heat
sozman wrote:
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It's not so much that it will hurt your yeast as the higher temps. will
hurt your beer.  You'll produce higher alcohols and phenolics that will
make the beer harsh and give you killer hangovers.
 
    ------------>Denny

--
Life begins at 60 - 1.060, that is.

Reply to denny_at_projectoneaudio_dot_com

Re: does fermentation itself generate heat
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balances):
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(snip)

Huh huh.  Chemistry is cool.  I used to think about this stuff myself back
in the day when I first started brewing.  This ain't nuts.  It's real
science.  Cool stuff, ain't it?

Actually, I believe there is supposed to be an oxygen molecule on the input
end of the chemical reaction.  And, not to be rude, but your equation above
does not balance properly.  Take, for instance, the Carbon atoms... if there
are 6 on the left, then there better be 6 on the right.  But anyway... I
believe that based on the amount of oxygen in the fermenting brew, differing
amounts of CO2 and alcohol will be produced, i.e., in the beginning stages
of fermentation, more CO2 is produced and less alcohol.  Then when the brew
is more anaerobic, more alcohol and less CO2.  Something like that anyway.
I've got it all in my old notes somewhere... fun stuff.

--
Dave
Bachelor of Chemical Engineering by degree



Re: does fermentation itself generate heat
There are six on the right. 2 from the CO2 (2 molecules) and 4 from the
ethanol (2 * 2 carbons in the molecule).

Of course, I'm a chem e, too, so I leave balancing to the chemists. I've
got better things to do....;^)

Chris

David M. Taylor wrote:
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Re: does fermentation itself generate heat
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Oops.  You got me on that one.  But you are basically right:  Fermentation
produces heat.

--
Dave
"Just a drink, a little drink, and I'll be feeling GOOooOOooOOooD!" --
Genesis, 1973-ish



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