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Calculated yeast attenuation

brendanc

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Hi all

I am planning my next brew to clone a beer, aiming to clone ABV  and FG as close as possible.

What is confusing me is how  Beersmith 2 calculates FG based  on the attenuation of the yeast in the recipe. I am going to use WLP570 which is listed as 73%  - 78% attenuation in the  ingrdient profile.

My recipe OG is 1.068 and BS2 predicts an FG of 1.005. The alcohol  and attenuation tool in BS calculates 1.068 to 1.005 as 90%attenuation, confirmed by another calculator.

So if the yeast in the recipe has a max attenuation of 78% why is it predicting 90% attenuation?

Help?
 
brendanc said:
So if the yeast in the recipe has a max attenuation of 78% why is it predicting 90% attenuation?

the 90% values does seem high. My first question is are you looking at the measured or estimated final gravity? without modifying the default recipe, all of the measured values are prepopulated with numbers that have nothing to do with the recipe.

In addition, it is possible to increase the fermentability calculation with low temperature mashes and decrease it with higher temps. The slope and center of this variable is found in Options > Advanced. Be careful, it's a global adjustment and will change all recipes.
 
Hi,

thanks for the reply.

The 90% attenuation is calculated using the predicted OG and FG of the recipe. To be honest this is the first time I am really aiming to hit a target FG and ABV% so I hadn't checked it against any of my previous batches, which we all great but not targeted to specific ABV%. Will go check my brew notes for the last few batches and then will CAREFULLY look at the setting under Advanced and see how that goes.

Cheers
Brendan
 
Much of the attenuation is based upon the type of sugars you are fermenting.  If you recipe contains a good portion of simple sugars (corn sugar, sucrose, honey, brown sugar, etc.), the yeast will pretty much fully ferment these out versus maltose derived from the grains/extract used.  This will be reflected in a higher calculated attenuation than is published for the yeast.  Those attenuation numbers are derived from use of a standard mash (all-barley malts) using a standard method.

It is not unusual for such high attenuation numbers to be achieved when brewing Belgian styles which contain a good portion of candi syrup.
 
Aaah makes sense, 15% invert sugar in this recipe.

Looking at my notes my last 5 malt only batches were pretty much bang on for predicted vs measured FG.

Thanks for help, am gonna brew on the basis whatever comes out will be drinkable
 
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