Calculating alcohol content in Cherry Wheat Beer

[brewdvm]

I brewed a really nice Cherry Wheat beer recently. I added 9 lbs of malt extract to the boil and fermented it 1 week before racking onto 10 lb of pasteurized cherries. I added this much malt extract because I erroneously assumed a dilution once racked onto the cherries. Here are the SG readings:
OG = 1.074
SG before racking onto cherries in secondary = 1.015
SG after racking on cherries with gentile mixing to avoid aeration = 1.020 (it went up due to sugar in mashed cherries)
FG = 1.013

Here’s how I calculated it. Since the cherries added 0.005 to the SG, I assumed I could add that to the OG. So 1.074 + 0.005 = 1.079 -1.013 (FG) x 125 + 0.5% for priming sugar fermentation = 8.75%.

Is that at all correct? Can anybody verify this or tell me how to calculate it the right way? Thanks.

[flars]

On line calculator comes up with 8.01%.

http://www.brewersfriend.com/abv-calculator/

Sorry, this is flawed.

[nighthawk]

Not quite correct. Yes the cherries added some residual sugars. I doubt 10lbs only added 1.005 to the batch.

I’m sure you had a new fermentation after adding the cherries? If so, the yeast ate much of the sugar from the cherries and created more alcohol. How much? Every crop of cherries will be a little different. You could search for a general number and try to calculate it.

An easier way would be to have a refractometer reading and your hydrometer reading for FG. With a calculator you can then get the ABV.

If we knew where you lived, someone near by may loan their refractometer to you.

[brewdvm]

Thanks for the replies. Yes, I did have a vigorous secondary fermentation after racking onto the cherries in secondary. I kept the blow off tube on which was a good idea since I actually did blow off some krauzen for the first 2 days. I left the cherries in for 12 days and then racked to tertiary. I then bottled 3 days later.

 I can get my hands on a refractometer.  Can you go into more detail here?  Are you using the Brix scale and somehow comparing it to the FG on the hydrometer?  Thanks again.

[brewdvm]

Another thought. I know the cherries had a lot of sugar (maybe I should have done a gravity on the juice before racking?), and the fermentation was vigorous, but I was also adding 5 gallons of almost fully fermented beer to this approximately 1 gallon of cherries. Wouldn’t that create quite a dilution? For example, let’s say the juice from these cherries had an OG of 1.055. The following equation might come close to a mixed beer / cherry SG?

1 gallon of mashed cherries at 1.055 + 5 gallons of beer at 1.015 / 6 gallons total volume = 1.020 This is of course not factoring in sugars left in the cherries themselves. Thanks again for the replies.

[nighthawk]

http://www.northernbrewer.com/refractometer-calculator/

Try these calculators when you get access to a refractometer.

Stop trying to “think” about the numbers and use some actual ones.

[brewdvm]

Thank you, Nighthawk! I cracked open a bottle and measured the Brix at 9.0. SG from hydrometer was still at 1.013 (beer was at room temperature). The calculator gave me an answer of 7.5%. It calculated an initial SG of 1.07 which was very close to the 1.074 reading I got. This is cool! Thanks again.