Low attenuation with dark beers

Has anyone had problems getting their dark beers(like stout or porter) to fully attenuate? I've done Denny's Porter, an indian brown ale, and 2 dry stouts. None of them finished with the gravity I expected. Most recently, I brewed a dry stout:

6 lb Pale malt
1.75 lb Flaked barley
1 lb roasted barley (crushed fine in electric coffee grinder)
.25 lb acidulated malt

hops: 41 IBUs
60 minute boil

My starting gravity was 1.038, which was a little low, but not a big concern because this is a session beer. I pitched Wyeast Irish Ale at 63F and let it rise to 65F. It was a little while before I saw any airlock activity, maybe 16 hours. Two days later there was no airlock actvity and the gravity was 1.014. I raised the temp by 1F each of the next three days and agitated the bucket to rouse the yeast. At the end of three days I got the same gravity reading. This gives an apparent attenuation of 63%. I pitched enough yeast after making a starter (according to mr malty). I mashed at 150F to get a fermentable wort and my thermometer is calibrated correctly. What might the problem be?

I guess it's a bad correlation(dark beer:low attenuation) since no one else has come to this conclusion. This time I'll chalk it up to Irish Ale yeast as a poor attenuator.

It is worth conmsidering that the sugars contributed by roasted barley may not be very fermentable since they are charred. 1 lbs of roasted barley I am assuming would have contributed about 4.7 gravity points to your beer (assuming 75% efficiency in a 5 gallon batch). It may be fair to assume that those are 4.7 points that will stick around. Some specialty malts and roasted malts will have their starches already converted before mashing and will contribute to the FG of your beer due to unfermentables.

Make sure you hydrometer reading are temperature adjusted. I recently made a lager from a similar dry stout recipe, og was same as yours at 1.038 but taken at 127 degrees. Various calculators have adjusted that up to 1.052 or so(don't remember the exact number). Hydrometers are idealized for 60 degrees.

Thanks for the replies. I took my OG at 63F, so it shouldn't need any adjusting. I just went back and looked at my recipe and it was 5.5 lb Pale malt, not that it matters. I agree that the rosted barley sugars probably don't get fermented. My recipe is based of Jamil's dry stout recipe and I think his FG was 1.010. 4 graivty points isn't that much, but since my OG started so low I think it is significant.

One more thing, I mashed my acid malt separately. I heard mash pH outside of normal range(5.2-5.5) can interfere with attenuation and extract tannin. Roasted barley already tanks it pretty low, so I did mine separately and poured it in prior to boil I had 75% attenuation after 4 days.

Maybe next time try something like 1335 (British ale II). I've had good luck with that one.

Lyikos said:

One more thing, I mashed my acid malt separately. I heard mash pH outside of normal range(5.2-5.5) can interfere with attenuation and extract tannin. Roasted barley already tanks it pretty low, so I did mine separately and poured it in prior to boil I had 75% attenuation after 4 days.

Click to expand...

I had thought about my mash pH being too low and planned on using some gypsum. Of course I forgot. I read that one of the amylase enzymes doesn't work as well in a low pH mash, so perhaps that was part of the problem. I did a 60-70 minute mash, and I don't do a starch conversion test. I guess I should start testing.

In regards to the yeast type, I could certainly pick a better attenuator. I'd probably just use us-05 because it gives a clean taste. But British II does look like a good option.

I did the BCS Dry Stout recipe with Wyeast 1056 and it went from 1.042 to 1.011 (65F for 4 weeks). I think going to a high attenuation yeast and doing a starter if needed for your volume (this is the only beer I didn't make a starter for because it was 3 gallons and low OG) will help along with the low mash temp. That recipe makes a great stout.

I was just reading through old posts regarding my own observations. Yes! All my beers darker than, say, 20SRM have shown less attenuation. My latest stout went from 1.046 to 1.014 using S05 at 70F, even though Beersmith predicts it will drop to 1.009. It tastes awesome and I'm not at all worried. It's just a concern on paper. Glad to see that others report similar things.

CanaBeer said:

I was just reading through old posts regarding my own observations. Yes! All my beers darker than, say, 20SRM have shown less attenuation. My latest stout went from 1.046 to 1.014 using S05 at 70F, even though Beersmith predicts it will drop to 1.009. It tastes awesome and I'm not at all worried. It's just a concern on paper. Glad to see that others report similar things.

Click to expand...

Yes, this reassuring. I'm convinced it is related to pH. A significant portion of dark grains, especially with acidulated malt added, may result in a pH below 5.1. I've begun to add my dark malts at vorlauf, rather than mash the full time. My last oatmeal came out with good attenuation using this method. Of course this is still speculation. I need to get a pH meter... Merry Xmas to me,

slarkin712 said:

Yes, this reassuring. I'm convinced it is related to pH. A significant portion of dark grains, especially with acidulated malt added, may result in a pH below 5.1. I've begun to add my dark malts at vorlauf, rather than mash the full time. My last oatmeal came out with good attenuation using this method. Of course this is still speculation. I need to get a pH meter... Merry Xmas to me,

Click to expand...

I'm not sure that makes sense. Bad mash pH would cause poor efficiency, but shouldn't have an effect on the sugars you are able to get out. It is more likely that it is either like cheier said and it's non-fermentable sugars from the roasted malts, or bad mash temp, or a combination of the two.

slarkin712 said:

Yes, this reassuring. I'm convinced it is related to pH. A significant portion of dark grains, especially with acidulated malt added, may result in a pH below 5.1. I've begun to add my dark malts at vorlauf, rather than mash the full time. My last oatmeal came out with good attenuation using this method. Of course this is still speculation. I need to get a pH meter... Merry Xmas to me,

Click to expand...

I wouldn't think that the pH would get that low, and even if it did, it would affect flavor but not fermentability.

Darker crystals and roasted malts have less fermentability that the lighter ones. That's a good thing, as I like my oatmeal stout to not be dry. Mash temperature can be manipulated to favor maltose over maltiose for better fermentability, but it sounds like you did that by mashing at 150.

Reviving an old thread.....

All three of my strong dark ale batches had attenuation issues. Every light, including my strong golden Belgians, fermented down to exactly where BeerSmith predicted. All temps were strictly monitored and confirmed with thermapen. I assumed that my starters were not large enough so every batch escalated in size. The final size was a two step, 4L each, starter.

1). I'm suspecting BeerSmith is not providing accurate results on beer darker than 40SRM. The maximum % of all dark malts (>120) never exceeded 15%.

2). Did anyone else have issues, not typically experienced, with Wyeast attenuation rates during 2017?

I've had Yooper's Oatmeal Stout in the fermenter now for three weeks. Denny's 1450. OG was right on target at 1.052. I checked the gravity at one week, it was 1.022. At two weeks it was the same. Every day for the past week I've been rousing the yeast. Since then I've been getting bubbles in the airlock but apparently no more fermentation, as I checked it again yesterday and it's still stuck at 1.022. I'm going to keep it in there one more week and then bottle next weekend regardless. The samples do taste good though. Hoping for the best.

Sounds like you're checking FG with a refractometer. That's won't work, you need a hydrometer.

The_Bishop said:

Sounds like you're checking FG with a refractometer. That's won't work, you need a hydrometer.

Click to expand...

Not sure who this is directed to, but if it's me I am using a hydrometer. Checked it with distilled water and it's reading correctly.

Same. Hydrometer...check. Distilled water....check.

Update. After a week of constant airlock activity (every 30/1min) gravity drop was zero.

I’ve reviewed everything (mash temps, yeast attenuation, oxygenation, yeast nutrient, pitching rate, fermentation temp) and my conclusion, by deduction, is still inconclusive. The only two possibilities left are:

1) Beersmith2 is not accurately representing dark malts/unfermentables. All of my light ales worked as predicted.

2) Advertised yeast attenuation is not accurate.