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Estimated ABV is higher than expected from my OG-FG calculations

chookherder

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Hi all,

Can you please advise what I am missing in this recipe? I have a estimated OG = 1.090 and a yeast Attenuation Max 82% but the Estimated ABV shows 10.6%.

My personal calculation estimates (1.090 - 1.016) x 131.25 = 9.7% ABV

Attached is the recipe, thanks in advance.

Kind regards,
Ben
 

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BOB357

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BeerSmith estimates are based on ingredients, the equipment profile and mash profile, along with your inputs. If you're using someone else's recipe, without knowing their process and efficiency, you can't expect to match their results. The odds of brewing the same recipe on 2 different systems and having the same results are slim and none.
 

crabbey

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From your recipe it Beersmith has calculated an FG of 1.0111 which feeds into its calculation of the est. ABV.

The Min/Max attenuation values for a yeast are not the only variables used to calculate the estimated attenuation, nor should they be.

HTH

Nathan
 

chookherder

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Thanks Bob,

It is my recipe, buy I think the answer to my question lies in the way Beersmith is calculating the Estimated Final Gravity.

I see Beersmith Estimates OG = 1.090 and Estimates FG = 1.011 , this would require 87.78% attenuation. The yeast profile I have selected shows a Max Attenuation of 83%.

So the question is "How does Beersmith calculate estimated attenuation, other than the selected Yeast 'Fermentation Range' values?"

Cheers,
Ben
 

chookherder

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Thanks Nathan,

You are absolutely right, do you know what the other factors ae?

I understand the factors to get lower than estimated attenuation, but not higher (without unexpected infections etc.)

Cheers
 

crabbey

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Oh and another thing, don't expect the (OG-SG)*131.25 to work in practice. In reality fermenting wort is much more complex to model that simply plugging in these numbers.

From my quantitative experience (using Anton Paar DMA35 and Anton Paar Alcolyser) the closest estimate I use is (OG-SG)*135. Again this is a simplistic estimate but it gets me close enough for the beers I produce. Note this does not match what Beersmith gives as an estimate. It will use a different estimation method.

Nathan
 

crabbey

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Hi Ben,

I don't know what formulae Beersmith uses under the bonnet, but by playing about you can get a feel for what influences what.

The estimated FG and therefore attenuation will be influenced by the fermentables used definitely the mash profile, and the yeast attenuation figures. Probably other things...

The min/max figures are probably based on published figures from the yeast manufacturers. They will assume a "normal" mash. However if you decided to make a super attenuable wort by mashing for hours at say 62 deg C and letting the beta amylase create a really high proportion of maltose, you'll find that you'll get a whole heap of attenuation over and above the published "maximum" attenuation.

 

chookherder

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Thanks Nathan,

Cool info appreciate your time. To be honest out of the 43 brews I've done with Beersmith it seems very close to expectations, just this wacky beer seemed to throw a curve ball.

I see the 'Session' tab down under the Fermentation timeline the pre-filled Gravity after Primary value is close to my expectation and the Gravity after Secondary is the same as the Estimated FG. So this is cool....but no matter what Fermentation Profile I choose these don't change.

Anyway it's all good, I love the tool and will take your advice and update my calculations to use (OG-FG)*135

Cheers big beers!
Ben
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Ben

 

GigaFemto

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You have some very low temperatures in your mash profile. BeerSmith uses those to estimate the fermentability of the mash. I think it uses the lowest one within the beta-alpha amylase range. It assumes, by default, a center temperature of 153.5 F and a slope of -1.25%/deg-F. At the center temperature I think it uses the median attenuation listed for the yeast. If you have a very low-temperature rest, even for a few minutes, BeerSmith will give you a very low estimate for your FG.

--GF
 

chookherder

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Thanks GF,

I certainly can affect the Est FG by playing with the mash temps, when I move the 60min rest to 153.5F the Est FG = 1.016 and the estimated attentuation matches my Yeast Max Att 80.9%.

So I guess we will wait and see how well it actually attenuates: I did mash at 65c (149F ) not the 67.5c (153.5F)

I brewed 5 days ago and yesterday the SG = 1.024 (still fermenting).

I will report back where it stops soon.

Thanks for the information.

Ben
 
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