Alcohol By Volume?

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MTBbrewer

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How do you figure your ABV when you add fruit into the secondary? OG was 1.068 and FG was 1.009 so I know I have at least 7.74%, but if the added sugar in the fruit ferments then there is no way to compute. Does anyone know a way, or is it just a guess?
 

Beernik

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Fruit does add sugar but it also adds a lot of water. I generally assume fruit as 5 to 9 ppg unless I'm using a puree.

As far as calculations go, it doesn't matter if you assume it's added in the primary or secondary.
 

buzzerj

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You can always measure the S.G. with a hydrometer before and after addition of sugars to the secondary and add the points to the O.G. to adjust the %ABV calculation. You add sugar late is the same as adding sugar at the start. Just add the points to the O.G. and subtract whatever the F.G. ends up being. So if O.G. is 1.060 and F.G. is 1.010 and you add sugars back to 1.020 and the final F.G. is 1.012, the % ABV is 0.058 x 131.25 = 7.6%. Let's say the O.G. was 1.060 and F.G was 1.010 and you added some unfermentable sugars to 1.020 and the final F.G. was 1.020., your %ABV would be 0.040 x 131.25 = 5.25% with a much sweeter result.
 

zoomzilla

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I'm dumb at math and have always wondered about this as well. Frankly I don't understand the formulas put forth. If I measure the OG that is the original gravity. It is the only thing that can be original. Then I measure the final gravity to determine abv. Additional sugar additions and how yeast process them seem to only mess these measurements up. If someone can explain this process to a drunk like me that would be fantastic.
 

Calder

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Just ignore it. Use your original OG and whatever the eventual FG is. Doing the calculation may upset you.

For most beers, the addition of fruit actually lowers the effective OG. Fruit contains roughly 10% of sugars per lb when compared to plain sugar. Of course it does vary by fruit.

Assuming your fruit has 10% sugars, 10 lbs of fruit made up to 1 gallon would give a gravity of 1.046. 10 lbs is a large volume. Some fruits that have about 10% sugar (by weight) are apples, blueberries, blackberries, cherries, kiwi, pears, and plums.
 

buzzerj

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I did. If you add a fermentable sugar anywhere during fermentation, the yeast will metabolize it and make more alcohol than before. So if your O.G. is 1.068 and your F.G. is 1.009 you would expect a %ABV of 1.068 - 1.009 = 0.059 (you with me so far?) 0.059 x 131.25 = 7.74% Some people multiply by 133 so it would be 7.85%. OK then lets say you add some fermentable sugar and your yeast's alcohol tolerance is 10% so your yeast will still ferment a wort up to 10% alcohol. And you add enough fermentable sugar to raise the 1.009 F.G. up 11 more points to 1.020. (you'd have to take a hydrometer reading after adding more sugar into the beer). So the yeast swimming around see the new sugar and say yum more lunch! They metabolize that sugar (airlock activity resumes). You take a final F.G. reading days later and it reads 1.008. 1.020 - 1.008 is 12 points. You can figure it one of two ways. Either 0.012 X 131.25 = 1.58%ABV and add that to the 7.74% ABV above and get an adjusted %ABV of 9.32%. Or you can add 12 points to your O.G. number 1.068+ 0.012 = 1.080 and subtract the final gravity 1.080 - 1.009 = 0.071 and 0.071 x 131.25 = 9.32%. Now do you see? So what was your hydrometer reading after you added the sugar and stirred it in? And what was the final gravity prior to bottling?
 

Calder

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I did. If you add a fermentable sugar anywhere during fermentation, the yeast will metabolize it and make more alcohol than before. So if your O.G. is 1.068 and your F.G. is 1.009 you would expect a %ABV of 1.068 - 1.009 = 0.059 (you with me so far?) 0.059 x 131.25 = 7.74% Some people multiply by 133 so it would be 7.85%. OK then lets say you add some fermentable sugar and your yeast's alcohol tolerance is 10% so your yeast will still ferment a wort up to 10% alcohol. And you add enough fermentable sugar to raise the 1.009 F.G. up 11 more points to 1.020. (you'd have to take a hydrometer reading after adding more sugar into the beer). So the yeast swimming around see the new sugar and say yum more lunch! They metabolize that sugar (airlock activity resumes). You take a final F.G. reading days later and it reads 1.008. 1.020 - 1.008 is 12 points. You can figure it one of two ways. Either 0.012 X 131.25 = 1.58%ABV and add that to the 7.74% ABV above and get an adjusted %ABV of 9.32%. Or you can add 12 points to your O.G. number 1.068+ 0.012 = 1.080 and subtract the final gravity 1.080 - 1.009 = 0.071 and 0.071 x 131.25 = 9.32%. Now do you see? So what was your hydrometer reading after you added the sugar and stirred it in? And what was the final gravity prior to bottling?
How do you account for the additional volume of liquid you added when adding the new fermentable sugars?
 

buzzerj

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Correct, depending on the net added volume of sugar solution. I was assuming the net volume was the same (as in adding fruit in a bag and removing it later). Let's say you added your 12 points of sugar in 0.5 gallons so the initial volume was 5 gallons and the final volume is 5.5 gallons. The ABV is Alcohol by Volume so if you increased the net volume by 10% (5.5/5 =1.10), you can factor that dilution by 0.071 divided by 1.10 or 0.0645. 0.0645 X 131.25 = 8.5%ABV for 5.5 gallons.
 
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MTBbrewer

MTBbrewer

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Lots of activity since I asked this question. Checking the sugar after I added the fruit is probably what I should have done. This is actually a Sour experiment and the fruit I added was 15oz of yellow raisins. The more I think about it checking the sugar after I added may not have worked since the raisins are dried up until they hydrate with the beer. Either way she started bubbling again.
 
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