Low attenuation

Levers101 · 10-06-2006, 04:11 AM

I just got done racking a stout based off of a Murphy's clone into secondary. My OG was 1.046 and my FG (at least going into secondary) is 1.016. This is only 65% attenuation. It seems a little low considering the Wyeast Lab's specs for their Irish Ale yeast is 71-75%.

Recipe as follows:

6 lbs Breiss gold LME
3.3 oz Muntons light DME

8 oz British Chocolate malt
7 oz Roasted barley
4 oz 50-60L Crystal malt
3 oz Coffee Malt

1 oz Target @ 60 min
1/4 oz Kent Goldings @ 15 min

Wyeast Irish Ale yeast #1084
Started with a 2L continuously stirred starter at high krausen
OG = 1.046
FG (@ 2ndary) = 1.016
Fermentation temp 70 deg F.

I did the whole shake the bucket deal after checking for completeness before all the krausen had fallen to resuspend the yeast. Is the residual sugar from all the unfermentables in the specialty grains?

I'm sure I have beer, and it tastes good flat. I'm just wondering if there is something more I should be doing? Or if this is expected with my grain bill?

**Yuri_Rage** · 10-06-2006, 04:26 AM

Your OG seems really low. I plugged this recipe into Beer Smith and came up with 1.071 for OG and 1.018 for FG (73% attenuation). Have you adjusted your hydrometer measurements for temperature?

Also, what is the "shaking the fermenter" technique during fermentation? I've heard of gently rocking it when you're using a highly flocculant yeast, but that shouldn't be necessary with the Irish ale yeast you used. If you're introducing oxygen after pitching, you run the risk of oxidizing your beer.

Levers101 · 10-06-2006, 02:33 PM

Your calculated OG seems pretty high to me, because even if I wasn't correcting for temperature, which I did, the difference would be only 0.002-0.003. But perhaps my cheapie hydrometer stinks.

In my case "shaking" = gently rocking. Poor choice of an action verb. I just tip it back and forth side to side inside my fridge.

**david_42** · 10-06-2006, 04:19 PM

I suspect your hydrometer. It is just about impossible to miss an OG by 25 points in an extract recipe. Even if your volume was 6 gallons instead of 5, your OG would have been 1.059. (this assumes "3.3 oz Muntons light DME" was really 3.3 pounds)

Otherwise, your hydrometer is ok and the low apparent attenuation is due to the high percentage of unfermentables in the specialty grains.

**Yuri_Rage** · 10-06-2006, 10:31 PM

Quote:

Originally Posted by david_42

(this assumes "3.3 oz Muntons light DME" was really 3.3 pounds)

Oops, I unintentionally made that assumption when calculating this recipe...if all you used was 3.3 oz of light DME, then see above for david_42's explanation.

Levers101 · 10-07-2006, 12:46 AM

Nope, my units were right--and no self-respecting engineer would have reported units wrong like that, ;-) (or your building collapses). I used 3.3 oz of Muntons on top of the LME to get to where I wanted the OG to be--which was what I measured.

I guess I'll see how it turns out when it is carbed.

**ajf** · 10-07-2006, 01:18 AM

The gravity will continue to drop in the secondary (although slowly).
I wouldn't worry.

-a.