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General Category => Yeast and Fermentation => Topic started by: cenosillica on July 17, 2011, 08:32:38 PM

Title: High Gravity fast fermentation?
Post by: cenosillica on July 17, 2011, 08:32:38 PM
I'm a little surprised to see how quickly this beer fermented. Eight days ago I made an Imperial stout with a SG of 1.096 measured by way of refractometer (I don't really use software, I just x4 to get my gravity so brix was originally 24). I took a reading today (8 days fermenting) and had 15 on the refractometer. I remember reading that you have to adjust your readings by refractometer due to the non-sucrose elements in the wort (e.g. alcohol). So by entering this in my brewing software calc, it tells me that 15 Brix of fermented wort is really 1.039.

The type of yeast I used was whitelabs WLP002 English Ale Yeast which is supposed to have an attenuation of 63-70%. I also created a 1L starter and added yeast nutrient along with a fish pump O2 diffuser stone for about 3 minutes. Currently, by my fuzzy math, I have an attenuation of 57% ((1.096-1.039)/1.096)=.57 right? I'd venture to say that I'm about 85-90% through the fermentation.

I'm going to let it sit for another week and check the gravity again. Come next Wednesday or Thursday I will raise the temp and give it a diacetyl rest then keg.

My question after a long winded background is if this is really possible to ferment an imperial stout or any high gravity style for that matter this quickly? Most of the recipes I have dealt with have been 4-6 weeks total fermentation time. I'm happy, don't get me wrong, just a little befuddled that it is fermenting so fast!
Title: Re: High Gravity fast fermentation?
Post by: a10t2 on July 17, 2011, 08:42:54 PM
What was the temperature? That's the biggest variable in fermentation time.

High or low gravity, ale or lager, I've *never* had a beer take four weeks to ferment out. If yours do, you have a problem.
Title: Re: High Gravity fast fermentation?
Post by: cenosillica on July 17, 2011, 08:56:14 PM
The first week it was at 70. The current fermentation temp is a high at 73 F (ambient temp of house thermostat). Inside the bucket, its probably even higher. I suppose that would attribute to a fast fermentation. I forgot to post that ever important detail.

Before I became an all grain brewer, I used to buy extract recipes online. I'm stuck on that paradigm in that they all say 4-6 weeks for fermentation. What is your average fermentation to keg/bottle time?
Title: Re: High Gravity fast fermentation?
Post by: morticaixavier on July 17, 2011, 10:16:23 PM
even if your gravity readings tell you it's done with a high gravity like this I would recommend giving it at least another couple of weeks before doing anything with it. Just because the yeast says 63-70% attenuations doesn't really mean that you will absolutly get within that range. in my opinion 1.039 is still way to high but that may just be me. Let it ride. and remember, yeast don't read the calendar.
Title: Re: High Gravity fast fermentation?
Post by: a10t2 on July 17, 2011, 11:04:38 PM
The first week it was at 70. The current fermentation temp is a high at 73 F (ambient temp of house thermostat). Inside the bucket, its probably even higher.

70°F ambient is far FAR too warm for almost any beer. Heck, 70°F fermentation temperature is too warm for most. That could be why the fermentation has (potentially) stalled out. Once activity started to slow down, the temperature in the fermenter probably dropped 10°F, and that will cause some strains to prematurely flocculate.

http://seanterrill.com/2009/05/20/regulating-fermentation-temperatures/

What is your average fermentation to keg/bottle time?

The average is ~14 days for an ale, 6 weeks for a lager (4 weeks at <40°F). That's assuming there's no secondary fermentation or dry-hopping, either of which would add about a week.
Title: Re: High Gravity fast fermentation?
Post by: Thirsty_Monk on July 17, 2011, 11:53:41 PM

What is your average fermentation to keg/bottle time?

The average is ~14 days for an ale, 6 weeks for a lager (4 weeks at <40°F). That's assuming there's no secondary fermentation or dry-hopping, either of which would add about a week.

I everything should ferment within 2 weeks (a few days + or -).
If this does not happen then you
1) underpitched
2) have temp swings when fermenting.
Dry-hopping is extra step so add some time for it.
Title: Re: High Gravity fast fermentation?
Post by: tubercle on July 18, 2011, 12:41:08 AM

 Come next Wednesday or Thursday I will raise the temp and give it a diacetyl rest then keg.


 You are already @ 73f which is about 10 degrees too high. What temperature were you planing to raise it to?
Title: Re: High Gravity fast fermentation?
Post by: bluesman on July 18, 2011, 02:11:51 AM
Typically, for high gravity ales, I like to pitch in the low 60's and let the fermentation rise up on it's own to about 65-68F. This practice keeps the esters and fusel alcohols at bay, and allows the beer to have a moderately fruity character.

In your case you can expect some higher levels of esters. Your beer should be okay, but try pitching lower and controlling your fermentation temps in the mid to upper 60's for ales, in an effort to produce better beer.