[wmlindel]

I cultured and grew up the yeast from Tripel Karmeliet. Pitched into all grain wort at 1.073 and it fermented vigorously and fairly quickly. As it slowed, I roused and upped the temps into the 70s. It finished at 1.024 and is sweeter than I would like, with an apparent attenuation of 67%. My question is this: would it be worth racking into a secondary and adding US-05 to attempt to get it to attenuate further?

[BrewBama]

I believe the taste of US-05 could mask your original effort.

[dmtaylor]

I say go for it, it's worth a shot.  It would be better to make a little starter from the US-05, to wake it up good before adding it in there.  The addition of actively fermenting wort is known as krausening and is better than just tossing a pack in without doing so, even for dried yeast.  Otherwise the inactive yeast might not wake up, outcompeted significantly by the yeast that's already in the finished beer.

[denny]

I'd start with a forced fermentation test. That will tell you whether adding more yeast will do any good.

[erockrph]

I'd start with a forced fermentation test. That will tell you whether adding more yeast will do any good.

If it's the same yeast strain, this is true. An alternate yeast, especially a more attenuative one, could potentially ferment beyond what the original yeast could do.

To the OP - I think Belle Saison would be a better choice than US-05 for getting some more attenuation out of a stuck fermentation, but it may have some flavor impact. In the end it's your call whether it's more important to get some more fermentation or keep the original yeast's flavor profile.

How much of a starter did you make with the harvested yeast, and how did you step it up? Maybe the pitch wasn't big and hearty enough to handle a full fermentation yet? If so, maybe you could get another starter going from the existing yeast and pitch it at high krausen.

[RC]

A forced fermentation test would indeed be useful. It will tell you if the yeast crapped out prematurely or if they simply finished attenuating the wort. If the former, adding more yeast (krausening) is the best choice. If the latter, you could add ultra-ferm. This would resume the attenuation without imparting flavors from some other yeast strain. Once the gravity and flavor are where you want them, cold crash asap to halt further yeast activity.

As a side note, that beer is 8.4% abv. Seems risky (?) to culture from a bottle that is who knows how old and this high an abv. I wouldn't be surprised if the yeast simply couldn't get over the finish line. And is the bottle dregs the same strain that was used to ferment? Not uncommon to use a different strain for bottling, although admittedly I don't know anything about this beer.

[denny]

I'd start with a forced fermentation test. That will tell you whether adding more yeast will do any good.

If it's the same yeast strain, this is true. An alternate yeast, especially a more attenuative one, could potentially ferment beyond what the original yeast could do.

To the OP - I think Belle Saison would be a better choice than US-05 for getting some more attenuation out of a stuck fermentation, but it may have some flavor impact. In the end it's your call whether it's more important to get some more fermentation or keep the original yeast's flavor profile.

How much of a starter did you make with the harvested yeast, and how did you step it up? Maybe the pitch wasn't big and hearty enough to handle a full fermentation yet? If so, maybe you could get another starter going from the existing yeast and pitch it at high krausen.

A forced ferment test doesn't use the original yeast.  I use bread yeast.  You're just trying to find out if there are any fermentables left.

[wmlindel]

Thanks for the input. The culture was in multiple steps - 10cc, 100cc, 1 liter then 2 liters. Knowing nothing about the qualities of this yeast, it may be a low attenuator and was finished. The flavor was excellent and hopefully with a clean strain, it won't impart any other flavors and the Belgian esters will still shine through. Fermentation test may be a good choice. Thanks for the help!

[HopDen]

Test first then add kveik strain.

[Iliff Ave]

I wouldn't rack to a secondary but 05 should work well depending on the fermentability of the wort. Champagne yeast could be an option as well...

[soymateofeo]

wth is a forced fermentation test?

[denny]

wth is a forced fermentation test?

It's a way to find the limit of fermentabiliy of your wort. You pull some wort,  add a bunch of yeast to it and keep it warm.  If it ferment, it means you have a yeast problem. If it doesn't, then your wort is preventing further attenuation.

[reverseapachemaster]

I would do a forced fermentation test before throwing more money into the beer but I would assume this is an issue with the yeast rather than an issue with fermentables.

Bosteel beers in general are sweeter than a lot of other Belgian beers so it may simply be that their yeast(s?) is not a fantastic attenuator like many other common Belgian strains. Some can be notoriously finicky about sugar composition, heat, rousing, etc. to get down to low numbers.

Sending in a neutral ale yeast to finish the job would probably be fine and not affect the yeast driven flavors from the Bosteel yeast. I would add nutrients along with yeast. If you want to keep to a single strain you may want to give it time and keep it warm. Sometimes those finicky Belgian strains will drag out the end of fermentation over a long period of time. If there are unfermented fermentable sugars then they aren't going away if you want to wait, check again and then make a decision about adding more yeast.

[majorvices]

I wouldn't think using a neutral yeast would affect the yeast flavors from the Belgian. If you really want it dry add a diastaticus yeast. It will definitely finish the job! (Belle Saison, for instance).