Gravity, Fruit, and Alcohol content

Will adding about 4-5 cups of watermelon juice to my secondary secretly affect my alcohol content?

I will be using an organic, fully ripened watermelon from a local farm. That means it have a higher sugar amount than most store bought melons.

If you get the alcohol content from subtracting the alcohol equivalent of the OG from the FG, then it would seem that adding sugar skews this number. If the basic science is yeast turns sugar into alcohol, then adding more sugar (which isn't taken into account in the gravity equation) would add more alcohol which isn't calculated. Right?

Is there a way to get a more accurate calculation?

 

My rule of thumb for fruit: 7 OG gravity points per lb of fruit per gallon of wort. You might get a little more sugar with juice than with whole fruit.

You can add it to your beer OG as if it was going in the primary to ballpark your FG.

You'll never know exactly how much sugar is in the fruit, so you can never be completely sure what the FG should be. However, unless you are adding huge amounts of fruit, it doesn't add a lot of OG. Therefore the FG won't be that different and the ABV won't go up very much.

 

"Gravity, Fruit, and Alcohol"

my new band name

 

Dont know if this helps, but when I was making a mead with multiple honey additions I took a gravity before and after every add to get the differnece and jsut kept a running total. Ended with a final SG 1.151 and FG 0.994 for an ABV of 20.6. It is currently aging, 6 months already will try for New Years Party.