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How to Calculate Wine ABV %

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DirtyDawg10

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I posted this in another thread but I think it gets lost because of the bad title of that thread :slp I figured I'd make a new one, so here goes.

Cool! Thanks...so I was taking a look online and from what I can see my wine's ABV is 12.34% does that sound right? (Starting SG=1.090 - Finishing SG=0.996)
I've gone to a few different places online to try and figure what the ABV of my first wine will be. Here's what I came up with...

Online Calculator (Brewer's Friend) - 12.34% ABV

Online formula from eHow - (1.090-0.996)1000)/7.36 = 12.77% ABV

Online Calculator (Vinter Resources) - 13% ABV

Can anyone tell me what they use to calculate ABV and which might be right? They are all fairly close but I like to be accurate. I figured you guys would have done this before and can steer me in the right direction. I looked but couldn't seem to find a sticky or recent thread about this on here. Thanks for any help you can give me.
 

Rocky

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DD, as you say they are all close. Do you know that the ABV as stated on a bottle of commercial wine can be plus or minus 1%? So what you see on those bottles is not dead on accurate either.

But, if you really want to do an accurate job and don't mind sacrificing some of your wine, try the following:

1. Take an accurate sample amount, say one pint.
2. Put the sample in a pot on the range and turn on the heat to medium.
3. Bring the wine to about 180 degrees F and keep it there for at least 15 minutes.
4. Remove from the heat and measure the volume of the remaining liquid.
4. Alcohol boils off at about 175 degrees F, water at 212 degrees F, so the change in volume will be the alcohol that is vaporized.
6. Divide the amount lost by the starting volume to give you the % alcohol in the original wine.

PS: This is a good method for determining alcohol when you forget or did not take an initial SG reading.
 
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DirtyDawg10

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Hmmm...didn't know that. I guess I'll pick the formula in the middle and split the difference. I'd rather not sacrifice the wine.

Thanks for the response Rocky. What do you use to calculate yours?
 

BobF

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I got used to SG - FG / 7.36, so I stick with it. As time has worn, I've become less CDO about how accurate I can calc the ABV.

Keep in mind that any method that depends on specific gravity readings can only be close.
 

cpfan

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Personally I use (1.090-0.996) * 133 = 12.502%

The factors 133, 7.36, 135, and others are used by various people. I have no idea which is perfect (and don't really care). The factor 133 comes out pretty close to the hydrometer that I use, so that works for me.

As BobF suggested, sg readings with a hydrometer are not perfectly accurate due to eyesight. Also there are temperature factors to consider (which personally I ignore).

Steve
 

sweetcheeks

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Blood brillian!

DD, as you say they are all close. Do you know that the ABV as stated on a bottle of commercial wine can be plus or minus 1%? So what you see on those bottles is not dead on accurate either.

But, if you really want to do an accurate job and don't mind sacrificing some of your wine, try the following:

1. Take an accurate sample amount, say one pint.
2. Put the sample in a pot on the range and turn on the heat to medium.
3. Bring the wine to about 180 degrees F and keep it there for at least 15 minutes.
4. Remove from the heat and measure the volume of the remaining liquid.
4. Alcohol boils off at about 175 degrees F, water at 212 degrees F, so the change in volume will be the alcohol that is vaporized.
6. Divide the amount lost by the starting volume to give you the % alcohol in the original wine.

PS: This is a good method for determining alcohol when you forget or did not take an initial SG reading.
This is bloody brilliant. Thanks so much. One to write in my journal!
 

DirtyDawg10

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Good info. I never realized it wasn't an exact science and that people use different formulas to calculate the %. Thanks for the help.

And I just realized that the x135 formula is the same as 1000/7.36 so I'll be using that from now on.
 

jswordy

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What's wrong with starting potential alcohol subtract finished potential alcohol? That's how I learned to do it.
 

BobF

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What's wrong with starting potential alcohol subtract finished potential alcohol? That's how I learned to do it.
Nothing wrong with it at all. Some folks might not have a PA scale on their hydro.
 

jswordy

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It's easy for math-challenged drunks like me! :dg

B&WS, you have to let me know when you next have a shipping special, please. I could easily have put money in your pocket that went elsewhere if I had known about that last one. Is there an email notification sign-in somewhere I can join?
 

winemanden

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Stop worrying about ABV being accurate.
Pour yourself a glass, look, sniff, taste, and look in the mirror. If you've got a pleased look and you feel good, you've got it right. Life's good, Enjoy it.

Regards to all, Winemanden. :h:h:h
 
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Qualitykez

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I'm also on my first batch of homemade wine and although I understand an accurate ABV reading doesn't really mean a great deal, whilst I have the home brewing bug I am reading as many tips and as much advice as possible, more out of impatience than anything else! I also have come across several variations of calculators however none of them state exactly whether FG is the reading taken once fermentation has completed or after the stabiliser and finishing agents have been added? Like most things in sure to the accomplished winemaker this question is probably silly and obvious but it's supposing how one word missing from a statement to a newbie like myself can make a whole world of difference in this instance, my SG was 1.082 after fermentation was 0.994 and after the stabaliser and finishing agent was 1.002 (I am brewing a young's 6 bottle Riesling) Any advice welcome
 

BernardSmith

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Qulaitykez, I am not totally convinced that James' calculator will answer your question. In part because it is not likely that adding stabilizer and a finishing agent would have any impact on your final gravity. But if what I am about to write more or less describes your wine then perhaps this might help.
Let's say your wine just before you stabilized was about 11 percent ABV (alcohol by volume). You stabilized it and you added some chemicals to finish and polish it and with those chemicals was some sugars to back sweeten. The sugars are not fermenting and that is how they sweeten. If the "six bottles" refers to the volume then we are talking about a large gallon or thereabouts, if the amount of stabilizing chemicals and the finishing chemicals and sugars did not significantly add to the volume then the estimated Alcohol By Volume (11 %) is not going to be affected (no increase in volume). The fact that the gravity has risen is because of the addition of sugar so that is NOT going to raise the gravity at which the wine stopped fermenting, so IF the wine's gravity was .994 it is still .994 and if the amount of sugar that was to be fermented at the start was 1.085 then it was and is 1.085 and neither figure has changed. IF the difference between those tow figures is about 11 percent alcohol then it is still 11 only now it is a sweeter wine.
Of course, if the finishing and clearing chemicals added substantially to the volume (substantially) then the AB by VOLUME would fall (if the volume was 5 Liters and now is 6 then you have added 20 percent more volume so the ABV would be reduced by about 1/5 but if the increase in volume was say, 50 ml then the change is insignificant and the error and inaccuracy of the estimation of the ABV mean that small changes in volume of the wine don't change the calculation of the ABV.
 

Qualitykez

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Thank you Bernard. That clears it up quite nicely (no pun intended)!! I eagerly await my first batch!! Thanks again
 

Yogi

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DD, as you say they are all close. Do you know that the ABV as stated on a bottle of commercial wine can be plus or minus 1%? So what you see on those bottles is not dead on accurate either.

But, if you really want to do an accurate job and don't mind sacrificing some of your wine, try the following:

1. Take an accurate sample amount, say one pint.
2. Put the sample in a pot on the range and turn on the heat to medium.
3. Bring the wine to about 180 degrees F and keep it there for at least 15 minutes.
4. Remove from the heat and measure the volume of the remaining liquid.
4. Alcohol boils off at about 175 degrees F, water at 212 degrees F, so the change in volume will be the alcohol that is vaporized.
6. Divide the amount lost by the starting volume to give you the % alcohol in the original wine.

PS: This is a good method for determining alcohol when you forget or did not take an initial SG reading.
I don't think this will give correct answer. When 1 ltr alcohol is mixed with 1 ltr water, the resulting volume of the solution is not 2 ltrs. It is less than 2 ltrs.
I don't know the exact % by which the volume of solution is less than 2 ltrs. But I am sure it is less.

Suppose it is 1.8 ltrs (hypothetically); and you boil it at 185 degrees for 15 minutes, and then measure the volume of remaining solution after evaporation of alcohol. It will come out to be 1 ltr.
By your method, the volume of alcohol will turn out to be 0.8 ltr... when actually it was 1 ltr.

I think, the correct method will be to find out the weight of solution before and after evaporating alcohol. Subtracting the final weight of solution from initial, you will get weight of alcohol. And then convert that weight into alcohol volume. That will be the correct volume.
Then you can find its volume % to solution volume before evaporation.. and you get your ABV.

I must declare that I haven't done this. I am no scientist, or a mathematician. I am just applying the logic on available facts.

Another correct method seems to be to distill and collect the evaporated alcohol and actually measure its volume.
 
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The formula I use (and I don't remember where I found it) is (S.G. - F.G). x 131.25
example (1.1 - 1.03) = .07 x 131.25 = 9.1875% ABV
 

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