Calculating ABV w/backsweetening involved...

[M38A1]

I've read quite a bit of threads on calculating ABV and have a pretty good understanding of a starting SG and the ending SG, then using something like BrewersFriend to calculate the ABV.

Where I'm stumped is once I have my ending SG, then toss the k-sorbate/k-meta at it to effectively kill the yeast production/protect the product, how is the ABV calculated when you add sugar at this point?

My beginning SG was 1.096
My ending SG was .990
If I understand correctly, my ABV is roughly 13.9%

But it needed some backsweeting so I added 1/2 cup sugar per gallon leaving me an SG of 1.010. Starting at 1.096 and finishing at 1.010 after adding my sugar, that gives me an ABV of roughly 11.29%.

I suppose the real question is, how is a final ABV calculation performed when back sweetening is involved?

 

[Scooter68]

Without further fermentation your ABV is not going to change just because you back sweeten unless you using large amounts of liquid. It would only decrease then because of the dilution.
If you are adding raw sugar and dissolve it you aren't going to effectively lower the ABV.

 

[M38A1]

That's sort of where my head was..... Kill the fermentation capability, kill the alcohol increase capability. And dilution would do just that, dilute both ABV and flavor.

Thanks for the reply! Looks like I've got a 13.9% batch this time with back sweetening added to my process.

 

[Noontime]

Yup, what Scooter said. It's alcohol by volume, so by adding sugar you are increasing the volume slightly, while the alcohol content stays the same. But unless you're adding huge amounts or adding it with water it's not really enough to effect a change. Using a simple syrup MIGHT make a slight difference, but going by SG calculations are kind-of a really close guess any way, not 100% accurate.

 

[Ajmassa]

My beginning SG was 1.096
My ending SG was .990
If I understand correctly, my ABV is roughly 13.9%

But it needed some backsweeting so I added 1/2 cup sugar per gallon leaving me an SG of 1.010. Starting at 1.096 and finishing at 1.010 after adding my sugar, that gives me an ABV of roughly 11.29%.

I suppose the real question is, how is a final ABV calculation performed when back sweetening is involved?

Just from a mathematical perspective- after backsweetening- when calculating new abv you’ve got .020 fermented SG units unaccounted for. So your starting SG becomes 1.116 instead 1.096 if “ending SG” is 1.010. and the abv remains the same.