Ways to Terminate Fermentation at a Desired FG?

[Protos]

Gentlemen, I'm trying to clone an old recipe that requires a Final Gravity of 1.030 (OG is 1.088, all-malt, no adjuncts). It's obvious the yeast in the original recipe is a much lower-attenuating one than any of what we have today. No ways to get such a high final gravity however I alter my mashing schedule (Lactose, Maltodextrine and other non-fermentables are out of question because that's a clone).
My question is, what methods you might suggest for terminating fermentation at a desired FG?
Pasteurisation? Adding some yeast-inhibiting chemicals? Or something else?

 

[magno]

Myself... I'd use a low-to-moderate attenuating yeast, like Windsor, mash on the high side, and get as close to 1.030 as I could without fretting too much.

Where did you find this recipe? What is the style you are cloning?

 

[Genuine]

I would mash on the higher side as well. 156-160 depending on what your recipe calculator is telling you. I've done this before with NEIPA's to have the FG finish in the 1.020-1.025 range without the use of lactose.

 

[MMP126]

You would be looking for a yeast to attenuate the wort to about 64%. This is pretty low, as most yeast attenuates to the mid 70s, or higher.

Most people touched on it, but, yes, mash at a higher temperature. 156F to 160F would be good. And use a lower attenuating yeast that matches your style. All reputable yeast companies will post the attenuation ranges for their yeast. Just find one with low attenuation, that works for the beer style.

I have never really tried to hard stop fermentation. So, I am not sure how that would be accomplished? You may be able to pasteurize, but I have heard that it can lead to weird flavors in the final product. And this sudden halt could lead to off flavors, as the yeast do not enter the "clean up" stage of fermentation, to rid any off flavors that develop during fermentation (Like Diacetyl and such).

I would do the high mash, and get a low attenuating yeast strain. You may not get 1.033, but with a high mash, and the right yeast, you should get close.

 

[Protos]

What is the style you are cloning?

It's a Latvian dark sweet lager, Dižalus ("Strong Beer"). I believe, the style emerged historically not without some influence of North German Mumme.
In this recipe, I need an apparent attenuation of 65%, while the least-attenuating Lager yeast I can put my hands on attenuates no lower than 72% at a single 68°C infusion.
Windsor would easily attenuate to 65% and stop there, but it is an Ale yeast, while I need a low-attenuating Lager.

That's why I'm thinking I have to terminate the fermentation at the desired gravity so I'm searching for the best method to do that.

 

[Protos]

And this sudden halt could lead to off flavors, as the yeast do not enter the "clean up" stage of fermentation, to rid any off flavors that develop during fermentation

Yes, that's what I'm afraid of.

 

[marc1]

Try mashing at 71C.

 

[hotbeer]

It'd seem that you'd want more unfermentable sugars in your wort and make certain that your yeast is not considered diastatic. Or what ever it is about a yeast type that lets it start breaking down the unfermentable sugar into sugars it can ferment after it's finished with the easy stuff.

So yes, I'd think mash at a higher temperature.

Might could just add some unfermentable sugars after the fact to bring the FG back up. Might give you an opportunity to adjust flavors if you use certain types. Not sure how well that works though.

And another method I've not ever seen anyone talk deeply about... pasteurization.

 

[VikeMan]

In this recipe, I need an apparent attenuation of 65%, while the least-attenuating Lager yeast I can put my hands on attenuates no lower than 72% at a single 68°C infusion.

Is there some reason you have to mash at 68C? If not, you could go higher and reduce the wort's fermentability. And you can also go shorter, like, say, 30 minutes.

 

[Protos]

No, no reasons to mash exactly at 68C. I mentioned that just to say that the lowest-attenuating Lager yeast available to me (S-23) attenuates rather high even at such a hot mash temperature. I did a beer with it at 68C once, and it attenuated up to 72%. Don't think it would attenuate significantly lower at 72 or 74C.
Anyway, the recipe must be brewed with a Hochkurz Decoction, so a single super-hot mash isn't an option in this case.

MMP126 is right: forced termination might cause off-flavours. Probably, adding non-fermentables remains the only option. Though that will make the beer not a clone anymore...

 

[VikeMan]

I did a beer with it at 68C once, and it attenuated up to 72%. Don't think it would attenuate significantly lower at 72 or 74C.

I bet it would. I don't think there's anything special about S-23 that would allow it to ferment dextrins bigger than maltotriose, which a warmer, shorter mash would make more of.

 

[Protos]

Well, that's quite probable, but the decoction required by the recipe won't let me to benefit from it.

 

[marc1]

Where did you get this recipe from? Is it a homebrew recipe or commercial?

 

[Protos]

The recipe is of an old commercial beer, adapted from some old brewing book. Very low attenuation, sometimes no more than 55%, was very typical for that time but nowadays those yeast strains are unavailable.

 

[Misplaced_Canuck]

Freeze the beer to 0C (32F) once you reach your desired FG. Don't do that in a glass carboy though!

 

[Protos]

Won't the yeast spring back to fermentation when the temperature rises back again?