Bad yeast, or just an unfermentable wort?

Assuming a proper amount of healthy yeast, what kind of attenuation should I expect from this brew?

“Oatmeal Stout”

70% Pale malt
11% Flaked oats/barley
11% Mid-range crystals
8% Chocolate/Roasted Barley

Mash 60 min @ 153

OG = 1.051

Fermented @ 68 degrees with Wyeast 1388 London Ale III; expected attenuation 71-75%

FG = 1.020

I have warmed and roused for a few days, and it’s looking pretty clear that the beer is stopping @ 1.020 for an apparent attenuation of 61%. (Assume hydrometer and user are both working correctly).

So either there is a problem (my yeast was poor to begin with or I somehow treated it badly), or there is not a problem and 1.020 is actually a natural stopping point based on my wort fermentability. I want to believe the latter, but 61% seems like a pretty long way from 71%.

According to Style Guidelines, an Oatmeal Stout finishes at 1.010 to 1.018. You're not too far off. Can you really tell your FG to within .002?

Time may tell. I have found most beers lose another .002 in the secondary.

how long has it been fermenting? i've just had a porter get down to 1.016 after one week, then it took the entire 2nd week to get down to 13.

however, that is a lot of unfermentables.

It'll will have been 8 days as of dinnertime this evening. It's soon, and I sound noobish whining about it, I know. But honestly, all of my ferments (the last 15?) get to within 1-2 points of FG after day 3 or day 4. So, it's usually around day 5 that I check. That's what I did this time, and I was @ 1.021. I roused and warmed for 2 more days, and it dropped to 1.020.

Maybe it'll drop another point... I'm not counting it out. I almost always give 'er 2 weeks in the primary no matter what. But based on previous experience I'm really not expecting it to drop another 5-6 points, which is what it would take to make Wyeast's 71% 'minimum' attenuation.

I do think it is a lot of unfermentables as well. 22% if you lump flaked and crystals together. So that's why I'm wondering if 62% attentuation is rather expected.

(I can read gravity very clearly to within .001 with my duplo-scale hydrometer).

Some of those English strains can be temperamental. If you had a sudden drop in temp towards the end of the ferment the yeast will drop out and stop working. This will leave you with a high finish gravity and an abundance of diacytle. When using these strains (and most any strain) it's a good idea to boost the temp towards the end to keep the yeast working.

As I said, I did boost. It's been warmed up to 72-75 degrees for the last 3 days. Last night I stirred with my thief and really broke up the yeast cake on the bottom.

I guess I'm really fishing for someone to tell me that 61% attentution is reasonable based on my grain bill and mashing regimen, but it seems like most folks are seeing this as a problem to fixed.

dang.

Judochop said:

As I said, I did boost. It's been warmed up to 72-75 degrees for the last 3 days. Last night I stirred with my thief and really broke up the yeast cake on the bottom.

I guess I'm really fishing for someone to tell me that 61% attentution is reasonable based on my grain bill and mashing regimen, but it seems like most folks are seeing this as a problem to fixed.

dang.

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yeah but if you had a cold snap before that it could have put your yeast to sleep. Once they fall to the bottom it's very hard to get them working again. Especially with a very flocculant strain.

maida7 said:

yeah but if you had a cold snap before that it could have put your yeast to sleep. Once they fall to the bottom it's very hard to get them working again. Especially with a very flocculant strain.

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Ah. I see where you're going, and it's a fair point. But to the best of my knowledge, they were cruising along @ 68, and it only went up from there.

What's the deal with sleeping yeast not wanting to wake up and work again, even after extreme rousing? That seems contradictory to the common practice of harvesting these same yeast and repitching them into a new wort. Yet if I pitch NEW yeast into my stuck stout, they might decide to finish the job? Or no? (Because if new yeast do decide to finish the job where the old yeast won't, it almost sounds as if these dudes are working based on a change in environment, like how poorly performing professional basketball teams suddenly go on a 5-game win streak when you replace their coach).

Judochop said:

Ah. I see where you're going, and it's a fair point. But to the best of my knowledge, they were cruising along @ 68, and it only went up from there.

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well then maybe temp is not the problem. It was just a guess. This time of year it's easy to get bitten by a cold snap.

Judochop said:

What's the deal with sleeping yeast not wanting to wake up and work again, even after extreme rousing? That seems contradictory to the common practice of harvesting these same yeast and repitching them into a new wort. Yet if I pitch NEW yeast into my stuck stout, they might decide to finish the job? Or no? (Because if new yeast do decide to finish the job where the old yeast won't, it almost sounds as if these dudes are working based on a change in environment, like how poorly performing professional basketball teams suddenly go on a 5-game win streak when you replace their coach).

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The yeast in your stout are under the influence of alcohol. You can understand that it's hard to get any work done under those conditions

For a new pitch to work it's best if they are at high krausen. But before you do that, I'd wait at least one more week and see if the gravity doesn't magically drop on it's own.

PS: have you confirmed that you mash thermometer is accurate? Was the mash extra thick? A thick hot mash can make an unfermentable wort

at 68F ferm temp I'm leaning more towards high amount of unmentionables and high mash temp (for this specific grain bill).

and possibly inaccurate thermometer.

motobrewer said:

at 68F ferm temp I'm leaning more towards high amount of unmentionables and high mash temp (for this specific grain bill).

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At last! The voice of hope I'd been waiting for!

and possibly inaccurate thermometer

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But then you had to go and ruin it with that. :cross:

Yeah, 1.020 is fine for that recipe. You've got 11% crystal, chocolate malt and oats, a moderate mash temp, and a moderate attenuating yeast. My oatmeal stout finished at 1.018, I believe.

Yooper said:

Yeah, 1.020 is fine for that recipe. You've got 11% crystal, chocolate malt and oats, a moderate mash temp, and a moderate attenuating yeast. My oatmeal stout finished at 1.018, I believe.

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Thanks Yoop.

A little baffled by how I could be seeing 61% attenuation for a strain that is listed with a range of 71-75%, I went straight to the horse's mouth with my question and asked Wyeast what exactly their attenuation ranges referred to. Their answer was rather enlightening, a bit shocking but also relieving.

Here's the convo:

MY QUESTION:
What assumptions about wort fermentability does Wyeast make when determining the attenuation variability range for each paticular strain? For example, does the low end of the range account for an unusually non-fermentable wort, such as one created using 30% specialty/flaked/roasted grains, and mashed at temps around 156F? Or do the ranges assume a 'normal' wort and reflect only variability within the yeast itself.

WYEAST RESPONSE:
The reported attenuation numbers are based on tests completed years ago (standard media) but are, in my opinion, considered obsolete. Over the last year, I have been working to reduce the importance assigned to attenuation numbers. Wort and fermentation conditions are far more important when considering the expected level of attenuation. Most ale strains attenuate to the approximately the same level (+/- 1.5%). Lager and Wheat strains will attenuate a little less (-1.5%).

I am currently working on assigning new numbers to all of our strains

It'll be interesting to see the 'new numbers' when they come out.

that is interesting.

Yeah with that grain bill I don't think you're going to get much lower.

JonK331 said:

Yeah with that grain bill I don't think you're going to get much lower.

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Good. Because the body feels just right where it is and I'm tired of waiting.

I'll take a reading tonight, and barring any shocking developments, I"ll be kegging it tomorrow.

Thanks for the words of comfort, fellas. I will toast to HBT when I crack the keg next week.