Surprising attenuation level for Imperial Stout

[QuercusMax]

Last weekend I brewed a decently big Imperial Stout (1.092 OG), aerated with a drill/paint stirred, and pitched a big slurry of US05. My mash temperature was around 158, and I mashed for 75 minutes.

I chilled down to 55 prior to aerating and pitching, and then put in my basement where ambient was around 60, and the temperature stayed pretty constant around 65 for the first 5 days. It started slowing down so I moved it to a slightly warmer room where it sat at 64.

I checked the gravity yesterday, and to my surprise it was down to 1.022! I was not expecting that at all. :rockin:

Is my beer ruined?

Seriously, though, is this a typical attenuation level for US05 aeration and a big pitch? This is the biggest beer I've made, so I don't really know what to expect here. I wasn't expecting quite this level of attenuation with such a high mash temp, not that I'm complaining.

 

[peterj]

You got around 76% attenuation, which seems about right. US-05 is a pretty high attenuator, though that does seem to be on the high side for a mash temp of 158F. What was the recipe like? How much cyrstal did you use?

1.022 sounds like a great FG for an Imperial Stout. Anywhere in the 1.020s I would say is good. I just brewed an RIS a couple weeks ago with an OG of 1.099 and I'm hoping it gets down into the mid to low 1.020s.

 

[ill4delph]

You got the attenuation that i was shooting for...my Imperial Stout was 1.090 and it finished out around 1.028. That was pitching 2 packets of Safale-05. I was shooting for around the 1.022 range but im happy with it where it is because it's got a bit more mouth feel to it. Going to keg with a bit of cold brewed coffee and let it sit until christmas....it's going to be goooooood.

 

[dankbeer]

The last time I used S-05 was on a pumpkin ale. I mashed in at 154 F, collected 6.5 gallons at 1.044 OG. Which fermented down to 1.007 (84% attenuation). I was also surprised when I saw how beastly this yeast was.

 

[QuercusMax]

My grain bill was:

18.2lbs American 2-row malt
4lb Dark Munich
1.0 lb crystal malt (120 °L)
12 oz. chocolate malt
12 oz. black patent malt
10 oz. roasted barley (ground to powder)
9.6 oz. flaked rye
8.0 oz. flaked barley

So I don't have much crystal. I boosted the base malt as I did a partigyle and made a 4 gallon 1.050 coffee milk stout (half pound lactose, extra half pound roasted barley).

I'm just hoping it doesn't drop too much farther! 1.022 seems like the perfect FG.

 

[peterj]

That's awesome, I did a partigyle with my RIS too. Ended up with a 1.037 beer that tastes a lot like a dry Irish stout. I didn't add anything to it, just drained my full volume for the RIS then took the 2nd runnings for the small beer. Made for a long brew day though because I only have 1 burner.