watermelon in beer - how much fermentable sugar?

[mitsitsad]

Hi all,

I made a brew at my homebrew club big brew day and its turning out nice so far. 1.078 OG pale ale (maybe imperial?) and I wanted to add a nice watermelon bite.

I took a reading today (brewed on Saturday, pitched chico yeast) and its at 1.020. I added 1 gallon of puréed watermelon and it's happily fermenting.

Anyway, I'm trying to figure out how much sugar this added to my beer to calculate FG numbers as well as abv. Any input would be appreciated. Cheers!

 

[chickypad]

With fruit you're likely not adding to the ABV because you're also adding volume/water. I've measured fresh squeezed watermelon juice at 1.030, so it actually dilutes the beer a bit when I add it. There is an article discussing this here.

 

[mitsitsad]

With fruit you're likely not adding to the ABV because you're also adding volume/water. I've measured fresh squeezed watermelon juice at 1.030, so it actually dilutes the beer a bit when I add it. There is an article discussing this here.

Maybe I don't know anything about this so if you could explain it'd be appreciated. Say my juice was what you measured (1.030) and 1 gallon. If this is the case, and my gravity at the time of addition was 1.020 (4 gallons), would it make the "new gravity" 4x1.020 + 1x1.030/5 = 1.022? Or is it OG which would be 4x1.078+1x1.030/5 = 1.068?

Or can I use them as separate calculations? Assume FG = 1.020. So for beer OG-FG = 1.078-1.020 = 7.6% and watermelon = 1.030-1.020= 1.3% for 8.9% total?

Sorry if it's a little confusing

 

[chickypad]

I think the OG formula you list would be correct. I don't usually bother trying to calculate since I'm adding like a quart of 1.030 juice to 5 gal of 1.050 beer, so pretty minimal impact (brings it to 1.049 if the math is right). Seems like you could just go with the newly calculated OG and the final measured FG though, unless I'm missing something. The trick is measuring the fruit I guess, juice is pretty easy.