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I'm a moderately experienced homebrewer, and recently I've been making a lot of imperial stouts--variations on the same recipe, hoping to dial it in. Decently strong ones: my OG is usually around 1.111, and I finish between 1.030 and 1.037 (I'm aiming for a sweeter stout, so that's fine). I pitch 2 rehydrated packs of Safale S-04 (new) per 5 gallon batch. I primary until it's done fermenting actively, transfer to a keg for secondary, and let it age for 1-2 months before crashing in the cooler.

However, I have a persistent alcoholic/solventy flavor when I first try the beers. This has happened 3 times now. Really hits you in the back of the nose when you sip/inhale over the beer. The rest of the flavors are fine; no weird yeast making nasty tastes.

I know that this is typically a fermentation temperature issue, but the odd thing is that, if anything, most of these beers ferment a little low (I have a poorly heated room for fermentation in the winter, so even with a water bath, the temps tend to stick between 58F and 63F).

What could be causing these alcoholic/solventy flavors? Should I lower the primary temperature still more?

Also, I've been taking the beer out of the water bath when it's done with primary and letting it secondary in the air. This might lead the temperatures to get somewhat higher during the days (though never more to 70F, and typically not for more than an hour or two). Could this be when/where the off flavor develops?

Could this be a symptom of stressed yeast? Should I pitch more/re-pitch during fermentation? Alternatively, is this a typical "young beer" problem with strong stouts, and one that will fade with time?

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How old are these beers when you start drinking them? Are they bottled? You mention a keg for secondary, but its unclear how quickly you are drinking them after that. I would assume a 12% stout would take no less than 6-7 months of conditioning to be palatable. –  Graham Apr 29 '13 at 16:31
    
Basically stressed yeast is right. Only time can help with a beer with a lot of fusel alcohols. Check out this page on fusel alcohols for more information: en.wikipedia.org/wiki/Fusel_alcohol –  Chris Plaisier Apr 29 '13 at 16:40
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1 Answer

up vote 5 down vote accepted

The problem could be from temperature, alcohol tolerance and pitching rates. While the solvent character will fade with time to some degree, it can take a many months to do so and will not completely disappear.

Although I can't find published figures from Fermentis, S-04 has reportedly an alcohol tolerance of 10-11% in various forums. Your 1.111 beer gives 12% abv so you are definitely at the upper end of what this yeast can do, which in itself may produce more higher alcohols. You might want to try knocking this back to 1.095.

2 Packets of rehydrated yeast will give 360 billion cells. (Assuming 90% viability since they are new.) For a 1.111 beer, Beersmith says you will need 480 billion cells, so this is quite a significant underpitch. Also with bigger beers you need proportionally more yeast - you really do need lots of healthy yeast for these beers to ferment clean. You can either pitch 3 sachets, or brew a regular strength beer and pitch the the yeast cake from that.

If you're not using yeast nutrient blend, that would be a good idea.

A temperature controller would also help. The natural temperature fluctuations in a house do stress the yeast to some extent for normal gravity beers, and that is emphasized with high gravity beers. The ambient temperature of 58F is definitely on the low side - S-04 has a recommended minimum of 59F - although with a beer this big the beer temperature could easily be higher during the first couple of days of fermentation. If Temperature Control is not an option now, you could try storing the carboy in a large bath of water - this will help smooth out the fluctuations and keep the beer temperature at the average temperature of your house.

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All of this is solid. In addition, you really need to oxygenate the hell out of a beer that big. I'd suggest 3 packets of something neutral, like US-05, with plenty of oxygen at pitching. –  Graham Apr 29 '13 at 16:34
    
I agree. I always oxygenate, so it slipped my mind. For a beer this big you could even oxygenate a day after pitching to provide for continued growth of the yeast, similar to staggered nutrient/O2 additions done for mead. –  mdma Apr 29 '13 at 19:14
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