ABV and Fermentation Time

This is probably a very naive question: say you're brewing a beer with an expected ABV of ~4% vs. a beer with ~8%. Assuming the same yeast is used for both, should the 8% beer take twice as long? Or does a beer with lots of fermentables ferment twice as fast?

I'm asking this because I'm currently brewing a Porter with a high expected ABV relative to previous beers I've made and I'm wondering how long I should expect fermentation to take.

i always use the 1-2-3 rule on all my beers no matter the gravity(excluding barleywines)
1 week in primary
2 weeks in secondary
3 weeks in bottles

I'm not a yeast expert, but I'm going to say from experience that a 1 week primary will be sufficient time for a beer to ferment in that higher ABV range. Assuming that the same amount of yeast is pitched in both your 4% and 8% brew, you might see a more vigorous fermentation in the 8% brew, but it should still start to reside in 2-3 days. Remember, the main bulk of you alcohol is produced in the first few days, no matter how much sugar is in the beer. The tail end of the primary you are just fighting over a couple gravity points.

deharris said:

This is probably a very naive question: say you're brewing a beer with an expected ABV of ~4% vs. a beer with ~8%. Assuming the same yeast is used for both, should the 8% beer take twice as long? Or does a beer with lots of fermentables ferment twice as fast?

I'm asking this because I'm currently brewing a Porter with a high expected ABV relative to previous beers I've made and I'm wondering how long I should expect fermentation to take.

Click to expand...

No, it won't take "twice as long" but it will probably take longer. There are far too many variables for it to be as simple as that.

- how many healthy yeast are in the wort (did you use a starter and what size starter?)
- What temperature are you fermenting at?
- what kind of yeast are you using?
- other conditions (aeration, nutrients, etc.)

even with all these variables, it would still be hard to determine the exact time when you fermentation will finish. you're talking about living creatures here.

This is why it is ALWAYS important to use a hydrometer. the 1-2-3 method "works" for most smaller beers, but it really cannot be used as a perfect rule because time really has nothing to do with whether or not your fermentation is finished.

EDIT: Also, just because a beer has reached it's final gravity, doesn't mean it's completely finished. many would transfer it to secondary at this point, others would leave it in the primary for an extra couple of weeks. During this time, the yeast will clean up after itself. your readings may not even drop, but be assured that your yeast are hard at work making a cleaner, tastier beer. Patience is a necessity for brewing good beers.