Brix calc ABV potential correlation to ABV calc results?

[mujin]

I put in a 20% brix value and get 1.083 SG and a potential ABV of 11.5%.
However if I use the ABV calculator entering 1.083 Initial Gravity and 1.019 Final Gravity (from the recipe) I get 8.4% ABV

Shouldn't these match?

 

[Nosybear]

I don't think the calculations use the same equation.... Looks like the difference between the classic ABV formula and the more precise alternate equation to me. The first calculation you mention assumes a FG of 0° Brix (Plato, but the two measurements are essentially equivalent) using the alternate equation and I get 11.49%. Using the SG figures you mention in the second scenario, I get 8.4% using the standard equation. So no, for the scenarios you outline, the results should not match. Here's my recommendation:
- Use the Alternate Equation for higher gravity brews (like yours). It's more accurate.
- Whether you use Brix/Plato or SG, always enter both values (OG and FG)

 

[BOB357]

The potential is a value you'd reach if the beverage fermented down to 1.000. Works great for estimating ABV for a dry cider, but not worth a hoot for beer.

 

[Yooper]

The potential is a value you'd reach if the beverage fermented down to 1.000. Works great for estimating ABV for a dry cider, but not worth a hoot for beer.

Right- the potential alcohol is the alcohol you’d have if every bit of the sugar fermented out to alcohol. Ciders and wines easily get to .990 and all of the simple sugars are fermentable. Beer, on the other hand has more complex sugars that do not ferment out completely and will often finish at 1.005-1.016 or so depending on the recipe and mash temperatures.