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Old 09-24-2007, 07:30 AM   #1
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Default % alcohol, time and fermentation

I am new to this hobby/art/science and I don't entirely understand how fermentation time, yeast, and alcohol content are related. I am yet to attempt my first batch, but in going over different recipes I would like to try 'some day' I became a little confused on this. Let me lay down what I think I know and then we can work from there.

Alcohol content is based largely on the quantity of sugars used and on the type of yeast chosen. As yeast changes sugars to alcohol it would seem to follow that more initial sugar would mean more alcohol later on. And, of course, a yeast must be chosen that can handle a sufficiently high alcohol content when shooting for more alcoholic final products. I made this inference in reading a recipe for pretty standard Pale Ale (the first batch I intend to start within the next couple weeks) and another for higher alcohol content Barley wine. The Barley wine calls for nearly double the sugar that the PA calls for.

Now, something that eludes me is how to determine how long exactly to ferment ones brew. It would seem to me fermentation is done when its done, when there really isn't much sugar left to convert to alcohol. But recipes seems to have this already worked out. For the PA recipe mentioned above, it says within 8-14 days the fermentation should be finished. However the Barley Wine recipe lists fermentation time cryptically as 7 months. Why does it take only 8-14 days to hit 4% and a full 7 months to hit 10-12%?

I am also curious on this point because the second batch I intend to work on is some kind of mead. I would like to start this shortly after I start the Pale Ale and I am shooting for somewhere around 10-15%. But how exactly to hit that is beyond me. I guess that should just mean more initial honey (but how much?) and more fermentation time (but how long?). I read somewhere good high alcohol mead like that takes 4-12 months, but that is a pretty big range.

Finally, I have also run into "double fermentation" in reading about higher content brews. What exactly is double fermentation? Is it related somehow to my questions above?

Thank you for your time, I would appreciate any advice you veterans out there could give a pre-novice like myself.

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Old 09-24-2007, 12:44 PM   #2
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Well, you have it right. Basically, it's done when there is no more fermentable sugar left to ferment. The time given is just a guideline of when to expect that. It is not the alcohol content that makes it take longer, really. It depends on many things, temperature, yeast, types of sugars, etc. When they give you such a long time for barleywine, it doesn't mean it actually takes that long for it to ferment- higher ABV beverages take longer to mellow and actually taste good. It finished fermenting way before that. If you have a reasonable temperature and good yeast, fermentation is fairly quick and then the yeast are just cleaning up after themselves. I use the 1-2-3 method (more or less) for ales- 1 week in primary, 2 weeks in the clearing tank (secondary) and then 3 weeks in bottles. For a lager, wine, etc, I change that as needed. Just because I leave it sit in primary for a week or 10 days doesn't mean it is actively fermenting that long. It usually ferments out in about 2-3 days and just quietly sits there the rest of the time.

Mead is make with honey, and honey is notoriously slow to ferment. It also takes a very long time to mellow and taste good. Anything around/over 14-15% ABV usually tastes like rocket fuel for the first year or two.

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Old 09-24-2007, 04:19 PM   #3
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that barleywine recipe sorta sounds like its taking secondary + aging time into account...more like a timeline from brew day to drinkable product, than true fermentation time frame.

Otherwise you've got it right, more fermentable sugar = more alcohol, and the more to ferment means more time needed. really strong stuff adds a steep incline to the bell curve for fermentation time frames.

also remember that not all sugars are can make a very malty, low alcohol beer that ferments quickly even though its got a high starting gravity.
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Old 09-24-2007, 05:11 PM   #4
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It should also be mentioned that you should always use (and trust) a hydrometer for every stage of your brew. It'll eliminate a lot of the guesswork for you. They're cheap and very easy. Just follow the instructions that come with the hydrometer and you'll be fine.
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Old 09-24-2007, 05:28 PM   #5
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Originally Posted by eddie
It should also be mentioned that you should always use (and trust) a hydrometer for every stage of your brew. It'll eliminate a lot of the guesswork for you. They're cheap and very easy. Just follow the instructions that come with the hydrometer and you'll be fine.
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