HOW DO I CALCULATE ALCOHOL FROM FRUIT?

[trucker5774]

The "dragon" wants me to make an AG beer with fruit (blackberries are all around at the moment) I was thinking probably just pale malt with perhaps cascade or amarillo to compliment the fruit. The plan (feel free to offer advice) is to add the fruit (pulped?) about two thirds through primary fermentation.

The question is .....if I add fruit part way through (or any other sugar for that matter) how do I work out the final ABV?

[trucker5774]

I have since noticed a thread on brewing a clear liquid to imitate a weak vodka. They add sugar late in fermentation............if anyone has the formula to calculate ABV it would be helpful to that thread to.

Is it as simple as adding on the increase in gravity then the usual calculation? This obviously won't work in the case of fruit as the sugar will take time to release, unless it's added as an "extract"

Any ideas?

[edit1now]

Strain some juice off the pulped fruit and measure the SG with a hydrometer. Rinse and sanitise the hydrometer and measure the PG of the fermenting beer. Assume the volume of the fruit to be all liquid (not very scientific ) and then work it out by:

Approx: PG of 20 litres of 2/3rds fermented beer is 1.020
SG of 3 litres of fruit is 1.040

ignore the 1 at the front of the gravities

Beer: 20 x .02 = 0.4
Fruit: 3 x .04 = 0.12
Add: 0.4 + 0.12 = 0.52
Total volume: 20 litres + 3 litres = 23 litres
Total gravity: 0.52 / 23 = 0.023 approx

put the 1 back in front = 1.023

when you put 3 litres of 1040 fruit into 20 litres of 1020 beer you get 23 litres at 1023

Measure the FG - say 1010?

From the point of adding the fruit you get a drop of 1023 - 1010 = 13 so use the HMRC fudge factor of 0.127 (for gravity drops between 10.5 and 17.2)

13 x 0.127 = 1.65 % ABV

Now what was the OG of the beer at the start of fermentation...? If we knew that we could get the overall ABV.

[trucker5774]

Thanks edit1now. I was trying to get my head around it. The fruit was throwing me. Assume the OG of the original brew was 1040, would you be good enough to complete the equation.....................seems a shame to have gone so far I'm not sure if I should calculate to the FG of the whole brew or to when the fruit was added

Your help is very much appreciated.............it's not expressed by enough people when a member helps out

[edit1now]

I think you add the drop from OG to PG to the drop from PG to FG, so if the PG of the beer is 1020, then

OG 1040 - PG 1020 = 20
HMRC fudge factor for drops from 17.3 to 26.1 is 0.128, so
20 x 0.128 = 2.26 % ABV

add 2.26% to 1.65% from my previous post = 4.21%

If you didn't add the fruit then if the FG is 1010 then
OG 1040 - FG 1010 = 30
HMRC fudge factor for drops from 26.2 to 36.0 is 0.129, so
30 x 0.129 = 3.87% ABV

Now try it with your actual figures?

[trucker5774]

Cheers edit, thanks once again