Length of fermentation vs. alcohol content?

Physics, chemistry and biology of brewing. The causes and the effects.

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Length of fermentation vs. alcohol content?

Postby Weiss » Tue Sep 28, 2004 2:42 pm

I'm making my second batch of Heart's Cream of Wheat beer. It's been about 12 days since I pitched the yeast, about 10.5 days since I noticed regular bubbles in the lock. Fermentation is down from the most active (bubbles every 5-7 secs), but it is still chugging right along at a big bubble every 20-30 secs or so.

Is there any type of correlation between length of active fermentation and final alcohol content, assuming a relatively strong and constant amount of bubbling? In other words, if I wasn't getting much activity, I wouldn't expect a particularly high alcohol content no matter what the length of fermentation was. But since it's been going constantly and for many days, is it possible I'll have a high alcohol content in the end?
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Postby Oldfart » Wed Sep 29, 2004 12:23 am

I don't think that the length of a ferment per se has much to do with alcohol produced by the ferment. I've got a fermentation going right now that is making about 3-4 bubbles per second, but it will be over quickly. You have a much slower fermentation, but longer lasting. Hard to tell if you or I will end up with more alcohol.
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Many factors to calculating Alcohol

Postby Azorean Brewer » Wed Sep 29, 2004 5:08 am


I believe that the alcohol content is a variable between the starting gravity and the final gravity, other variables will be ingridients, type of yeast, fermentation temperature, etc ...

From my experience it has nothing to do with the fermentation time exactly, providing the beer ferments out completely, but more to do with the delta difference between O.G. and F.G. A simple light beer conating adjuncts (Rice, Maize, etc ...) might finish lower than say a beer containing high levels of specialty malts.

The easiest way to calculate your alcohol is to take the starting gravity O.G. (example 1.048) and subtract the final gravity F.G. (example 1.012) from it, you then yeild 1.036 delta, eliminate the 1. so you have 036 or 36 delta, divide that number by 7.5 and you will have approximate alcohol level of 36/7.5=4.8%.

Becareful not to leave your beer on the yeast cake too long (more than 7-10 days) as you may experience undesirable off flavors. My recommendation is after 7-10 days rack it off to a glass carboy for secondary, there you can leave it up to 3 weeks or longer if you are lagering.

Hope this helps ...

"I drink therefore I am"
Azorean Brewer
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Postby Weiss » Wed Sep 29, 2004 1:39 pm

Thanks, guys.
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