Beer Math

[william_shakes_beer]

I would like to verify my description below for calculating the % alcohol of Apple Jack is correct.

I am making the classic Cider with 5 gallons of cider, 2 pounds of brown sugar and WLP 775. In past batches I have determined that my % alcohol was 10%.

If I then jack it by freezing and removing water, is the resulting alcohol percentage a simple linear function or are there other variable involved? Here is what I think the calculation should be:

OV=original volume
OA=Original alcohol
FV=Final Volume
FA=Final Alcohol
Jack=OV/FV

Given: OV=5 gallons
FV=2.5 gallons
OA=10%
Jack=0.5
FA=Jack*OA=20%

Does this sound reasonable?

 

[brewSJ]

It might still work in terms of volumes (I'm a physicist, not a chemist), but it's a lot easier to just work with weights. Let's make up some numbers. Suppose you start with 10g of alcohol in 100g of solution (i.e., 90g of water) so your starting ABW is 10%. You then remove 50g of water (in the form of ice). What you're left with is 10g of alcohol and 50g of solution, so your new ABW is 20%. As long as you don't remove any alcohol, the math is really easy in terms of weights.