Beersmith 3 FG vs yeast attenuation

[Bullhog]

I assume there is a logical reason for this, but can someone explain why BS3's FG is lower than the given yeast's attenuation? For example. Let's assume a lager with a light body mash @ 145, with Mangrove Jack M84 with an attenuation between 74-76. Let's say this yields an OG of 1050. At 76% attenuation, you should get a FG of 1012, but BS3 says 1008. What am I missing here? 1008 assumes an attenuation of 84.

edit: technically the recipe I put in has a step mash 125/145/158/168. I don't think the temp really matters though since it's predicting over attenuation, but maybe it's a software thing.

edit 2: if you go into advanced settings and uncheck "adjust FG for Mash Temperature" then it is correct, but I feel like this shouldn't be the case.

 

[VikeMan]

Couple of things...

Every yeast strain can attenuate both below and above its stated range. There is nothing special at all about the manufacturer's stated ranges.

Mash temperatures do matter. Beersmith does use mash temp and mash length when predicting attenuation. It also may be worth being aware that BeerSmith does not take the makeup of the grain bill into consideration when predicting attenuation.

edit 2: if you go into advanced settings and uncheck "adjust FG for Mash Temperature" then it is correct, but I feel like this shouldn't be the case.

By doing that, you are undoing the predicted influence of your step mash on attenuation. I wouldn't do that if I were you.

 

[Bullhog]

Every yeast strain can attenuate both below and above its range.

But 76 max attenuation vs 84 predicted attenuation is out of line right?

 

[VikeMan]

But 76 max attenuation vs 84 predicted attenuation is out of line right?

Not necessarily. As I said, there is nothing special at all about the manufacturer's stated ranges. i.e. there's nothing "max" about that 76. Assuming you have a grain bill with relatively little (or nothing) in the way of dark malts or crystal malts, and given those mash temps, 84% doesn't seem out of line at all (at first blush) for any of czech lager yeast strains I've used.

Note: I'm not saying that 84% is "right." If you want to post your grain bill, I can see what BrewCipher predicts.

 

[Bullhog]

I'm not saying that 84% is "right." If you want to post your grain bill, I can see what BrewCipher predicts

That sounds good. 9 lbs pilsner (weyermann) 14.4 oz Dextrine malt

 

[VikeMan]

That sounds good. 9 lbs pilsner (weyermann) 14.4 oz Dextrine malt

Ok, with your grain bill, yeast, and step mash, I'm getting a predicted 81.4% apparent attenuation. And just as an illustration of how grain bill matters, if I make that 100% pilsner malt I get 84% apparent attenuation (which happens to agree with BeerSmith, even though it arrived there via different models).

 

[Bullhog]

Ok, with your grain bill, yeast, and step mash, I'm getting a predicted 81.4% apparent attenuation. And just as an illustration of how grain bill matters, if I make that 100% pilsner malt I get 84% apparent attenuation (which happens to agree with BeerSmith, even though it arrived there via different models).

Thank you! Interesting stuff.