Low Attenuation w/ Maris Otter?

[deisty]

We've run into a strange issue with our BSI1 (Chico) ale yeast when fermenting any of our Maris Otter base brews, particularly our IPA. Yeast seems to reproduce well according to cell counts and ferments strong until around 70% attenuation and then fermentation ceases, or slowly drops for anywhere from 4-6 additional days and yeast health at harvest is terrible. We've typically seen 80+% attenuation in the past and we still see that activity on non-Maris Otter brews (and non-BSI1 brews). I'd like to get this yeast to attenuate back to 2.5-3 plato rather than the 4.5-5 plato it's finishing at for our IPA. I've been brewing on this system for 2.5 years and this is a new issue within the past 6 months. The troubling part is that we're not seeing similar behavior across all brews so it's been difficult to pinpoint the cause. We typically brew 15-17 bbl batches.

Facts:
1. IPA OG is roughly 15.0. This is our highest OG regular brew.
2. DO at knockout is 11-13 ppm. Constant for all brews.
3. Fermentation temp is 68, knockout temp is slightly lower. Constant for all BSI1 brews.
4. Pitching at a million c/ml/p at 90+% viability. Constant for all BSI1 brews.
5. Yeast nutrients provided in boil at 15 minute mark.
6. Malt analysis for Maris Otter shows no drastic variance between batches.
7. Typical mash temp is 156, mash and wort pH within acceptable range.
8. Strike water total alkalinity typically 100-120 ppm.
9. Sparge water <170 degrees.

We thought aeration was for sure the cause but have confirmed our O2 flow at knockout and swapped out our O2 stone as well. We're now focusing on hot-side and wort quality. Given the facts above, can you think of any hot-side causes of this yeast performance? I combed through all the yeast threads and couldn't find solutions that seemed applicable to our situation. Any feedback would be appreciated. Cheers.

[freysbrewing]

7. Typical mash temp is 156, mash and wort pH within acceptable range.

Yeah, we ran into this a few times as well. We'd never had the issue until a new brewer came on board and suddenly it started happening with him (he wasn't used to our system) and since we brew with a mash tun we built, it took a bit of head scratching. Here's a list of things that may help:
1) Probably not it, but check your temps with a few different thermometers.
2) Are you measuring your mash from the top, or do you have temp probes inside? If from the top, since this is an IPA, the depth of the mash bed is likely different than your other beers. Are you using a 4" thermometer on a 2' deep mash vs your other beers, which might be 1' deep? (Remember: heat rises). If from mounted temp probes, do you have enough to cover the extra area the IPA requires?
3) since it's an IPA, some of the malt may be sitting in one area (and not getting quite up to temp), but other parts of the mash tun are getting overly heated and causing your finishing issue. We found what was happening with ours, and it came down to how he was putting the grain in. It was not getting an even spread when the grain was going in and even though it was getting stirred, one side was hotter than the other (e.g., a hotter area and a colder area). Had the brewer spread the malt around and mix in the grains more evenly (e.g. darker malts didn't get one side only) when putting it in the mash tun and that stopped our issues.


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[deisty]

Thanks Freysbrewing, I think you are definitely correct that our mash temp readings need improvement. We've also found that MO has relatively low diastatic power and the DP has dropped pretty considerably over the last 3 batches of malt. We'll need to insert a bit more of a mash rest than we are currently doing. That combined with proper mash temp readings should really improve our consistency and attenuation.

[liammckenna]

I encourage you to consider yeast health and nutrition as well as Temp and malt.

What generation of pitching yeast are you at? How often do you re-propagate, introduce new yeast?

Do you use yeast food?

Fermentation stresses the heck out of yeast. Especially higher alcohol ones.

Interesting article here. http://youngscientistssymposium.org/...f/Lawrence.pdf

Good luck,

Pax.

Liam