understanding fermentablity numbers

[GeneDaniels1963]

I am fairly new to ale brewing, been doing wines for years. I am trying to understand the "fermentablity" on extract. For example, most Briess DMEs say they have 75% "fermentablity." Does that mean that only 75% of the sugars are available to the yeast? Therefore, it seems to me that attenuation numbers on the yeast, say 80%, would be taken factored from the percentage of the wort that is actually fermentable, the 75%?

Say I make an all extract wort OG 1.080, which gives me a PA of 11% ABV. But since only 75% of the sugars are fermentalbe, PA is really only 8.25%. Then, to account for the yeast, with an estimated attenuation of 80%. So 8.25 x 80% = 6.19%. Is that really what I am to expect as the final product?

 

[Gnomebrewer]

Yeast can ferment 100% of short chain sugars (glucose, sucrose, fructose - as long as they have enough nutrients), regardless of the attenuation listed for the yeast. The yeasts attenuation is a guide, given a typical all malt wort. Different yeasts ferment varying amounts of other sugars, right up to some diastatic strains that can ferment close to 100% apparent attenuation by cutting the longer chain sugars (and sometimes starches) into fermentable shorter chains. I'd assume that the '75% fermentability' listed by briess is the average for typical yeast fermenting that extract; i.e. fermentability is 75%, not 80% of 75%. 75% apparent attenuation means a 1.080 wort would finish at 1.020, which gives an ABV around 7.9% according to brewers friend. 80% apparent attenuation would give an FG of 1.016 and ABV at 8.4%. IME grain brews tend to attenuate a bit better - bigger beers that are all extract can benefit from some dextrose or table sugar to help drop the FG a bit (depending on what you're aiming to brew).

 

[Steveruch]

I got an extract brown ale with specialty grains down from 1.050 to 1.007 with nottingham: 86%.
5 gallons
5.5 lbs Briess golden light lme
1 lb. victory malt
10 ozs. crystal 60 malt
5 ozs. pale chocolate malt.

 

[GeneDaniels1963]

Yeast can ferment 100% of short chain sugars (glucose, sucrose, fructose - as long as they have enough nutrients), regardless of the attenuation listed for the yeast. The yeasts attenuation is a guide, given a typical all malt wort. Different yeasts ferment varying amounts of other sugars, right up to some diastatic strains that can ferment close to 100% apparent attenuation by cutting the longer chain sugars (and sometimes starches) into fermentable shorter chains. I'd assume that the '75% fermentability' listed by briess is the average for typical yeast fermenting that extract; i.e. fermentability is 75%, not 80% of 75%. 75% apparent attenuation means a 1.080 wort would finish at 1.020, which gives an ABV around 7.9% according to brewers friend. 80% apparent attenuation would give an FG of 1.016 and ABV at 8.4%. IME grain brews tend to attenuate a bit better - bigger beers that are all extract can benefit from some dextrose or table sugar to help drop the FG a bit (depending on what you're aiming to brew).

So that is it. They reflect estimated the yeast attenuation in their "fermentable" numbers. Thanks for explaining.