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Old 09-12-2010, 10:47 PM   #1
brad26
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Jun 2010
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Does anyone know what actually happens, after fermentation has completed, inside the beer. I know flavors and aromas change, but I'm just curious as to WHY that happens. What chemically is actually going on in there?

 
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Old 09-13-2010, 01:02 PM   #2
ajdelange
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Quote:
Originally Posted by brad26 View Post
Does anyone know what actually happens, after fermentation has completed, inside the beer. I know flavors and aromas change, but I'm just curious as to WHY that happens. What chemically is actually going on in there?
Lots and lots of things. Most striking (and perhaps of most concern to brewers) are
1) Acetolactate which has leaked out into the beer is nonenzymatically oxidized to diacetyl which is then taken up by the yeast cells and reduced to acetoin and 2,3 butanediol which have much higher taste thresholds
2) Acetaldehyde is taken up by the yeast and reduced to ethanol.

There is a whole thread on these 2 reductions here but much of it is devoted to pedantic bickering over the details of how they take place. There is a useful tip on how to test for diacetyl in your beer, however (at the end).

Many other perhaps less dramatic flavor changes take place as well. Sulfides (jungbuket) get scrubbed out by CO2, other aldehydes get reduced, the CO2 bonds with the beer in some mysterious (to me anyway) manner, flavors mellow. I'm sure if you search the literature you'll find hundreds of papers on these as sending stable beer out from the brewery is a big concern for commercial operators.

 
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Old 09-13-2010, 02:20 PM   #3
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aj,
I've seen this debated back and forth and don't think I ever saw a consensus but do you think there is any difference between force-carbed and naturally-carbed beer (all other things equal so to speak)?
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Old 09-13-2010, 06:25 PM   #4
ajdelange
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CO2 is CO2 is my take on it but there is certainly something in being able to say "naturally conditioned". If you want to thoroughly scrub out the smelly "green beer" volatiles I figure you have to let all the CO2 produced by the yeast go and actually carbonate with CO2 from a bottle. Of course the big guys capture CO2 from the fermenter, clean it up and then put it back into the beer. I think that's the only way Biersteuergesetz allows.

 
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Old 09-13-2010, 08:20 PM   #5
Fletch78
 
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I aged an oatmeal stout for 6 months in secondary, it tasted delicious when I bottled it. Now that it has carbed naturally in the bottle, it tastes like I just cooked it up last week.

 
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Old 09-13-2010, 11:17 PM   #6
-TH-
 
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Originally Posted by ajdelange View Post
CO2 is CO2 is my take on it but there is certainly something in being able to say "naturally conditioned". If you want to thoroughly scrub out the smelly "green beer" volatiles I figure you have to let all the CO2 produced by the yeast go and actually carbonate with CO2 from a bottle...
I always thought that some/most of the "green beer volatiles" were a result of the priming sugar and the yeast feeding on it - which would only be present when bottle conditioning. No?
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Old 07-22-2011, 04:32 PM   #7
Aunt_Ester
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Bump.

Quote:
I aged an oatmeal stout for 6 months in secondary, it tasted delicious when I bottled it. Now that it has carbed naturally in the bottle, it tastes like I just cooked it up last week.
Quote:
I always thought that some/most of the "green beer volatiles" were a result of the priming sugar and the yeast feeding on it - which would only be present when bottle conditioning. No?
I've surrendered to this hypothesis, too. I'd like to hear more experienced squabbling about the effects of conditioning. Like Fletch, I almost feel like the aging process has to start over when bottle conditioning; whereas, the flavor does not change when artificially carbing.

 
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Old 07-22-2011, 05:30 PM   #8
ajdelange
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Quote:
Originally Posted by -TH- View Post
I always thought that some/most of the "green beer volatiles" were a result of the priming sugar and the yeast feeding on it - which would only be present when bottle conditioning. No?
Don't think so because beer that is not primed has them too.

 
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