Brewing Master

Question:

says… Interesting.  I’ve never *really* understood the whole thing, myself. I just checked my spreadsheet calculator, and it first converts to degrees Plato, and then converts from apparent extract to real extract.  But the formula it gives for Alcohol % w/v is:

Mike, which spreadsheet are you using? Can you post a link? Thanks.

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I know that you can measure the alcohol precent of your beer by subracting FG from SG and multipling by 131. My questions are: What percent does that give you, alcohol by weight or alcohol by volume? What is the difference between the 2? How is the other one calculated? Which one of the 2 is the % that is listed on commercial brews? Sorry for all the questions, but I’m still a little hazy on this particular subject and would like to clear it up. Thanks for the help. Kyle

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I know that you can measure the alcohol precent of your beer by subracting FG from SG and multipling by 131. My questions are: What percent does that give you, alcohol by weight or alcohol by volume?

Volume. What is the difference between the 2?

25% How is the other one calculated?

ABV/1.25 = ABW or ABW x 1.25 = ABV Which one of the 2 is the % that is listed on commercial brews?

Most do ABV Sorry for all the questions, but I’m still a little hazy on this particular subject and would like to clear it up.

No problem. Cheers, Mike

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Excellent, exactly what I was looking for. Thank you Mike. – Hide quoted text — Show quoted text – I know that you can measure the alcohol precent of your beer by subracting FG from SG and multipling by 131. My questions are: What percent does that give you, alcohol by weight or alcohol by volume? Volume. What is the difference between the 2? 25% How is the other one calculated? ABV/1.25 = ABW or ABW x 1.25 = ABV Which one of the 2 is the % that is listed on commercial brews? Most do ABV Sorry for all the questions, but I’m still a little hazy on this particular subject and would like to clear it up. No problem. Cheers, Mike

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Which one of the 2 is the % that is listed on commercial brews? Most do ABV

Have they finally all standardized on ABV?  I thought it was the case years ago that most American megaswill beers listed ABW, while imports were ABV.  I can’t say I pay much attention to what the % is when I buy commercial beer anyway, so my info may be way out of date. John. —                            *** John P. Kolesar ***            *** Head Administrator, Monty Python’s Flying Talker ***

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Which one of the 2 is the % that is listed on commercial brews? Most do ABV Have they finally all standardized on ABV?  I thought it was the case years ago that most American megaswill beers listed ABW, while imports were ABV.  I can’t say I pay much attention to what the % is when I buy commercial beer anyway, so my info may be way out of date. John.

I think this varies by state.  In Washington, for example, it’s illegal to state the alcohol content on the label (go figure).  Some states *require* it, and I’ll bet they each have their own preference for ABW and ABV. Regards, Mike

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- Hide quoted text — Show quoted text – I know that you can measure the alcohol precent of your beer by subracting FG from SG and multipling by 131. My questions are: What percent does that give you, alcohol by weight or alcohol by volume? What is the difference between the 2? How is the other one calculated? Which one of the 2 is the % that is listed on commercial brews? Sorry for all the questions, but I’m still a little hazy on this particular subject and would like to clear it up. Thanks for the help. Kyle

At the risk of causing some folks to sputter and spit their beer, I don’t believe the "131 method" (i.e. 105 * 1.25) is really correct.  AbW needs the Final Specific Gravity to be used as a divisor in the calculation.  (And 1.25 is pretty close, but 1.26 or 1.27 is closer to the reciprocal of 0.79). Is this heresy?  Have I dwelt in darkness in this matter?  I’m not trying to stir up an argument, and apologies if this has been discussed before. Doug

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At the risk of causing some folks to sputter and spit their beer, I don’t believe the "131 method" (i.e. 105 * 1.25) is really correct.  AbW needs the Final Specific Gravity to be used as a divisor in the calculation.  (And 1.25 is pretty close, but 1.26 or 1.27 is closer to the reciprocal of 0.79). Is this heresy?  Have I dwelt in darkness in this matter?  I’m not trying to stir up an argument, and apologies if this has been discussed before.

Ok, technically all the calculations are estimates.  The alcohol percentage changes as the gravity of the beer changes. What I mean by that is it is not a linear calculation. 0.131 or 105 *1.25 is pretty darn close to the average. Now, back to your reciprocal discussion.  Try any number of calculations, and you will find this to be the case.  Let’s talk percentages.  20% of 1 added back to itself is 1.2, so it looks like 80% divided into 1 would yeild 1.2 also, but it doesn’t, it yeilds 1.25. The exact reciprocal of 1.2 is 0.833333. Anyway, where are you getting the 0.79 in the first place. There are many, many different formulas for calculating ABV, and the absolute easiest is (OG-FG)*0.131 where OG and FG are in points (1.050 = 50 points). Cheers, Mike

Response:

- Hide quoted text — Show quoted text – At the risk of causing some folks to sputter and spit their beer, I don’t believe the "131 method" (i.e. 105 * 1.25) is really correct.  AbW needs the Final Specific Gravity to be used as a divisor in the calculation.  (And 1.25 is pretty close, but 1.26 or 1.27 is closer to the reciprocal of 0.79). Is this heresy?  Have I dwelt in darkness in this matter?  I’m not trying to stir up an argument, and apologies if this has been discussed before. Ok, technically all the calculations are estimates.  The alcohol percentage changes as the gravity of the beer changes. What I mean by that is it is not a linear calculation. 0.131 or 105 *1.25 is pretty darn close to the average.

Yes, the changes in specific gravity represents changes in the percent alcohol, and this change is continuous until fermentation is complete.  But the calculation of AbW at the end of the fermentation process is not an average.  At the end of fermentation there is an amount of alcohol and an amount of beer, no longer changing for all practical purposes, which can be measured/calculated. You know the weight of the alcohol in the vessel and the weight of the beer (fsg) at the end of the process, so what is the percent?  Although the 131 method is close for AbV,  I was simply saying that the calculation is really more than 105 * 1.25, so why not include the rest? Now, back to your reciprocal discussion.  Try any number of calculations, and you will find this to be the case.  Let’s talk percentages.  20% of 1 added back to itself is 1.2, so it looks like 80% divided into 1 would yeild 1.2 also, but it doesn’t, it yeilds 1.25. The exact reciprocal of 1.2 is 0.833333. Anyway, where are you getting the 0.79 in the first place. There are many, many different formulas for calculating ABV, and the absolute easiest is (OG-FG)*0.131 where OG and FG are in points (1.050 = 50 points).

The reciprocal issue was to say that the weight of ethyl alcohol is 0.79 kg/L. So 0.79 is used as a divisor (or  1.26 as a multiplier) in the AbV calculation. (osg – fsg) * 131 is indeed easy to remember, even fairly close, I’m just saying it’s not complete.  At the end of fermentation, you can calculate the weight of alcohol, you know the weight of the beer (if fsg = 1.02 then the beer weighs 1.02 kg/L), and can therefore do a simple percent.  But that percent uses the fsg.  And you can use the weight of alcohol (0.79 kg/L) to convert AbW to AbV. Cheers, Mike

Time for a homebrew! Regards, Doug

Response:

- Hide quoted text — Show quoted text – I know that you can measure the alcohol precent of your beer by subracting FG from SG and multipling by 131. My questions are: What percent does that give you, alcohol by weight or alcohol by volume? What is the difference between the 2? How is the other one calculated? Which one of the 2 is the % that is listed on commercial brews? Sorry for all the questions, but I’m still a little hazy on this particular subject and would like to clear it up. Thanks for the help. Kyle At the risk of causing some folks to sputter and spit their beer, I don’t believe the "131 method" (i.e. 105 * 1.25) is really correct.  AbW needs the Final Specific Gravity to be used as a divisor in the calculation.  (And 1.25 is pretty close, but 1.26 or 1.27 is closer to the reciprocal of 0.79). Is this heresy?  Have I dwelt in darkness in this matter?  I’m not trying to stir up an argument, and apologies if this has been discussed before. Doug

Interesting.  I’ve never *really* understood the whole thing, myself. I just checked my spreadsheet calculator, and it first converts to degrees Plato, and then converts from apparent extract to real extract.  But the formula it gives for Alcohol % w/v is: ((OE-RE)/2.0665-0.010665*OE)/100 Where: OE is Original Extract in degrees Plato RE is Real Extract in degrees Plato It gives Alcohol % v/v as: ABW * (FG/0.794) Where: ABW is Alcohol % w/v FG is Final Gravity So for the Barleywine I just kegged (which is quite good, BTW!), I get 11.0 % v/v 8.60 % w/v which is closer to 1.28…(1.279) Either way, though, 11% v/v or 8.6% w/v is gonna give me a buzz!  I’d better bottle it up before I’m tempted to drink the whole thing. YMMV! Regards, Mike Sharp

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