How does Beersmith calculate %AA

[mr x]

I originally asked about this on a couple other boards, and didn't get many takers, so I'll throw it out again here:

Does anybody have any idea how Beersmith/Promash calculate %AA (apparent attenuation)?

For instance, my grain bill for JZ's Southern English Brown contains 6 lbs of 2 row, and 2.5 lbs of specialty malts (crystal, carafa, etc). Jam the numbers into Beersmith with my wYeast strain, and it gives me an O.G. and an F.G., with the F.G looking like it's calculated from the Average AA for that yeast strain in the Beersmith database. (I am using 1469VSS, and I copied the 1968 specs into the Beersmith database for it)

Now, if I use 8.5 lbs of 2 row in Beersmith, and compare with an equal O.G. of crystal 80l, I get almost the same AA (1.6% difference, the wrong way AFAIAC)).

For example:

8.5lbs UK 2 row and wYeast 1968 gives an OG/FG of 1.041/1.013
8.75lbs of crystal 80L and wYeast 1968 gives an of 1.041/1.012

Beersmith says a beer made of 80l crystal should attenuate better than a beer made of 2-row. Shouldn't there be a bigger difference than that in F.G.?

In JZ's original recipe, aren't 2.5 lbs of specialty malts pretty much non-fermentable (crystals, chocolate, etc). Shouldn't Beersmith calculate a significantly higher F.G. for the 2-row/specialty malt SEB recipe?

I look at the recipe I brewed (from JZ's book), with it's target AA, taste my sample, which I measured at 7% lower AA than the target and Beersmith calculation, find it's pretty good (that's the best I can do descriptively), and wonder, are the given AA numbers right?

[BeerSmith]

Hi,
  The apparent attenuation numbers can be calculated by hand as follows:
    apparent attenuation = ( ( OG in points - FG in points ) / OG in points ) x 100

Cheers,
Brad

[mr x]

Where does the F.G. get calculated?

[BeerSmith]

For the actual attenuation it uses the FG you enter.  For the "estimate" it uses the estimated OG which is primarily a function of your yeast attenuation and OG estimate.

Cheers,
Brad

[mr x]

I think you are missing my point. Beersmith estimates F.G. incorrectly in many cases. For instance, if you make a beer with 100% lactose, it should not ferment at all. But Beersmith will show an F.G. that indicates full fermentation. As in my example above with crystal malt.

[MaltLicker]

A friend and I looked at AA% a while back and thought that BS uses the average attentuation %.  This was purely based on swapping from high attenuators to lower ones and watching the stats change. 

I just created a basic small-batch test, swapping 7# of 2-row (Briess; PPG of 1.037) for 7# of roasted barley (generic; PPG of 1.025), at 75% EE%. 

For the OG/FG numbers, I got 1.053/1.013 (pale) and 1.036/1.009 (roasted), so it would appear to be working on the OG.  32% less PPG led to 32% less OG. 

I don't know about pure lactose, but I 'believe' that the diminished fermentability of roasted is reflected already in the 32% lower Potential Points per Gallon.  Roasted barley, the crystals, etc., are "steep only" grains, so the sugars already converted by the malting process, although lower, should still ferment out at the same AA%, here being 75%.  That seems correct here, going from 036 to 009. 

The two grains you mentioned are PPG of 1.036 and 1.034, much closer, and you added an extra 1/4# of the 80L, effectively compensating for the slightly lower PPG, thereby equalizing the total OG and FG from each grain, as your numbers indicate. 

The crystals, roasted, etc., are slightly less fermentable and that's reflected in their PPG.  I think where we start talking about significant "unfermentability" is when the proportion or raw amount of crystal grains gets large in relation to the base grains, as in your SEB, with 2.5# crystal in 8# total, or 31%. 

Hope that helps. 

[mr x]

I am very surprised that the roasted barley fermented out like that. Everything I have read indicated that there would be next to no fermentable sugars in a grain roasted to that level. For example:

http://www.vikingmalt.com/ourproducts/robarley.html


If that is not the case, my assumption could be wrong.

[MaltLicker]

I would agree with the zero enzymes on any roasted malt.  Perhaps by "fermentable extract of RB is minor" they mean additional extract that we could extract in the mash?  The PPG that the maltster created in the malting/roasting process is what it is, per the grain analysis sheet, which is what Brad puts in his database, just like ProMash, BeerTools et al. 

As an aside, this is also how seemingly identical recipes generate different OG specs.  One 2-row may have a PPG of 38 and another has a PPG of 36, and with 14# of either that would result in a slight difference in gravity, all else equal. 

[mr x]

I took the fermentable extract comment as meaning the extract was not fermentable, but I am sending them an e-mail to be sure.