How Do You Calculate Alcohol Content

Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum

Help Support Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
upperNY01brewer

upperNY01brewer

Well-Known Member
Joined
Mar 14, 2010
Messages
398
Reaction score
6
Location
Hamlin, NY
I did my first Cider a few weeks ago and today transferred to my secondary. My original gravity reading was 1.080, and todays reading is at 1.000. I have been taking readings on a regular bases and have seen a steady drop.

So what calculation do you use to figure the alcohol content. I know from the samples that I have drank it sure seems strong so far.
 
Gravity difference x some number, and possibly x some other number for one of the other alcohol calcs.
I've seen it say 129 through 131 and I'm sure there's some sort of reasoning for it.
http://beeradvocate.com/articles/518
It goes something like 1.080-1.000 is a gravity diff of .08
.08 x 131 = 10.48 abv
10.48 x 1.25 = 13.1 abw
 
As stated there are a bunch of calculators online. I have a couple wine books at home though that have the calculation in them. When I get back home in a day or two I'll find them and put them up so that way it's available for everyone to do on the fly.
 
KevinM said:
Gravity difference x some number, and possibly x some other number for one of the other alcohol calcs.
I've seen it say 129 through 131 and I'm sure there's some sort of reasoning for it.
http://beeradvocate.com/articles/518
It goes something like 1.080-1.000 is a gravity diff of .08
.08 x 131 = 10.48 abv
10.48 x 1.25 = 13.1 abw
Click to expand...

Not to pick on you specifically, since I've seen so many other replies that say the same thing -- so I'm saying this to everyone who gives a questionable formula without attribution, but:

That makes no sense.

You just pick a number between 129 and 131 and multiply it by the difference in the gravities -- and there you have it??

Why not pick the number 2,339.7? Or Pi? Or the measurements of "Miss December"?

I think what everyone is asking for is WHY do we use those numbers? And no saying 'Because that's what works'.

Brewing is as much a science as it is an art -- and if we can't explain how or why we do what we do, then we don't really know what we're doing.


So.... anyone want to explain how we calculate ABV?
 
Fionnbharr said:
Not to pick on you specifically, since I've seen so many other replies that say the same thing -- so I'm saying this to everyone who gives a questionable formula without attribution, but:

That makes no sense.

You just pick a number between 129 and 131 and multiply it by the difference in the gravities -- and there you have it??

Why not pick the number 2,339.7? Or Pi? Or the measurements of "Miss December"?

I think what everyone is asking for is WHY do we use those numbers? And no saying 'Because that's what works'.

Brewing is as much a science as it is an art -- and if we can't explain how or why we do what we do, then we don't really know what we're doing.


So.... anyone want to explain how we calculate ABV?
Click to expand...

Read the article from Wiki that I posted.. I know wiki is user-edited, but it's quite good in these instances.
 
Clann said:
The formula is Og - FG x 131.25 = ABV
Click to expand...

So, with an OG of 1.060, an FG of 1.010, we'd get:

1.060 - 1.010 x 131.25 =

1.060 - 132.5625 = -131.5025

An ABV of "negative 131.5 percent"? I don't think so.

This is exactly why I pointed out early on in this thread that so many replies to the question in the OP blindly give a formula without understanding it or citing a source.

In this case, the 'Order of Precedence' is incorrect: you subtract first, THEN multiply that difference -- not the way it's written above (where the FG is multiplied by 131.25 before being subtracted).

Brewing is as much a science as it is an art -- and if we can't explain how or why we do what we do, then we don't really know what we're doing.
 
It's an interesting read; One has to know the Original in Degrees Plato, and the Final in SG to use the calculation properly, which is weird.

Of course, I got little sleep overnight; coffee hasn't kicked-in. I'll look at it again after I've had more of my Organic Hot Roasted Bean Juice Homebrew.
 
Well, I did mention in my post that I didn't know the reason why the number was used and that I'm sure there's some reason behind it. I just didn't look it up yet. Heck, only found a few references because I had looked it up that previous night. And I at least gave a link to something that showed how they calculated it.
Which leads me to ask Fionnbharr... with all your complaining about not giving the right calculation or order of operation... why haven't you looked up the calculation and given us mathematical reasoning? And do you have one other than wiki?
 
KevinM said:
Which leads me to ask Fionnbharr... with all your complaining about not giving the right calculation or order of operation... why haven't you looked up the calculation and given us mathematical reasoning? And do you have one other than wiki?
Click to expand...

I don't have one other than Wikipedia -- I'm away from home at the moment (hooray for vacations!). I use a spreadsheet formula to do the calculation at home, which I built using a reference in a college-level biology text.

The calculation is fairly straightforward as I recall, and is based off the molecular weights of sugars, carbon dioxide and ethOH. When I get back to it, I'll post a link or an explanation.
 
Cool. There hasn't yet been a reason for me to know, other than being asked once, so I didn't even bother calculating before. until looking up the simplistic calculation for a closer estimate. I was curious about the 131ish number, but it's not important enough for me to look further right now, and the wiki page didn't want to load (404).

If I ever make something worth labeling, perhaps I'll pay attention to it, or if I feel like submitting something. Half the time, I haven't been taking my gravity readings either, since I haven't gotten to a brewing point where I'm making subtle adjustments.
 
KevinM said:
Well, I did mention in my post that I didn't know the reason why the number was used and that I'm sure there's some reason behind it. I just didn't look it up yet. Heck, only found a few references because I had looked it up that previous night. And I at least gave a link to something that showed how they calculated it.
Which leads me to ask Fionnbharr... with all your complaining about not giving the right calculation or order of operation... why haven't you looked up the calculation and given us mathematical reasoning? And do you have one other than wiki?
Click to expand...
Have to agree with you, being Im the original poster of this question and was just putting this out there looking for a simply answer that I thought someone here on the board would have a quick answer to.
 
KevinM said:
Cool. There hasn't yet been a reason for me to know, other than being asked once, so I didn't even bother calculating before. until looking up the simplistic calculation for a closer estimate. I was curious about the 131ish number, but it's not important enough for me to look further right now, and the wiki page didn't want to load (404).
Click to expand...

I'm guessing it comes from the mass of ethanol/ the mass of CO2 times the density of ethanol (46.069/44.01*.789). That gives you ~1.326 which, if you want an output that is 100 times the actual number (i.e., 9 '%' instead of .09) would be 132.6. It's not exactly correct still though, since the actual formula is:

(OG-FG) * (1.326 / FG)

But since it is assumed that most final gravities are close to 1.01 it is fair to round the 1.325 number to 1.31, then just multiply by 100 to get it in % terms.

It's just an easy way to get close to the actual ABV.
 
and the short explanation of THAT is that we are converting sugar to ethanol and CO2... sugar being the 'difference in gravities' we measured. We are of course assuming that nothing but pure ethanol and CO2 are being produced, and that we are only converting from sucrose, but it gets you really close to an actual ABV.

I think a high precision measurement with a refractometer and a final gravity will get you a more accurate ABV, but who really cares?
 
I actually will. Well... once I get this stupid sorghum to malt correctly. Cause then I'm definately going to need solid numbers and calculations beyond this to find out everything, including RS. No casual guesstimating at that point. I'm also going to want refine it down to get repeatable results and known constants. You know... once I can get the first step working.
 
Also, nobody has mentioned the fact that the temperature makes a difference... I am guessing that accounts for the variation in the number you are all using. There are plenty of good references online that explain the whole process and give a means of accounting for temperature variation.

And of course, you might have trouble getting an EXACT reading for some of the reasons stated above, including the fact that other reactions may be going on that affect gravity but don't produce alcohol, and sometimes not all the sugar may be fully dissolved, etc. Without expensive equipment and lots of experience, you are only going to be able to get close. Of course if you do it right, you should easily be within +-0.2% or so
 
Fionnbharr said:
So, with an OG of 1.060, an FG of 1.010, we'd get:

1.060 - 1.010 x 131.25 =

1.060 - 132.5625 = -131.5025

An ABV of "negative 131.5 percent"? I don't think so.

This is exactly why I pointed out early on in this thread that so many replies to the question in the OP blindly give a formula without understanding it or citing a source.

In this case, the 'Order of Precedence' is incorrect: you subtract first, THEN multiply that difference -- not the way it's written above (where the FG is multiplied by 131.25 before being subtracted).

Brewing is as much a science as it is an art -- and if we can't explain how or why we do what we do, then we don't really know what we're doing.
Click to expand...

No.

1.060 - 1.010= .050

.050 x 131.25 = 6.5625 or 6.5 ABV
 
Clann said:
No.

1.060 - 1.010= .050

.050 x 131.25 = 6.5625 or 6.5 ABV
Click to expand...

Sorry; the calculation you made of 6.5 ABV is incorrect, given the way the equation was written.

If you remember back to fourth grade math class -- there's something called "Order of Precedence" when it comes to doing calculations. One of the rules is that multiplication and division are performed before addition and subtraction, unless the numbers are grouped with parenthesis. The way the response above is written, the "Og - FG x 131.25 = ABV" implies the FG is multplied by 131.25 first.

This is basic math.

That was my point in my reply above -- where I got the obviously wrong answer of 'negative 131.5'. Far too many homebrewers blindly use formulas to prepare or understand their brew without understanding why we do what we do. My worry is that if we don't understand, then wrong information gets spread around.

Yes, we all understand we multiply the difference in gravities. We are somewhat experienced.

But what if we don't understand it, or don't have that experience? Someone reads "The formula is Og - FG x 131.25 = ABV", applies basic math rules, and gets the wrong answer.

The formula, as written, is incorrect.
 
ThunderPanda:

The variation in the number (the one near 131) comes about because it is dependent on the original gravity, not temperature. In the OG ranges that we routinely brew to, the number changes slowly over that range, so we can give a reasonable approximation at 131.

The conversion of sugars to alcohol is straightforward, but not linear. And the rate (the speed) of conversion is dependent on temperature, but the quantity (the amount) is NOT dependent on temperature. If we don't know the temperature, but we know the beginning and ending gravities, we can still determine the ABV.

Temperature makes a difference in the gravity reading (if you're using, say, a hydrometer), not the 'true' gravity. It's the reading that depends on temperature, not the ABV calculation. You use the 'true' value of the gravities in the calculation.
 
Here you go... (OG - FG) x 131.25 = ABV. Now it's written properly. Which reminds me... I need to go find the calculation in the wine book.
 
Sorry; the calculation you made of 6.5 ABV is incorrect, given the way the equation was written.

If you remember back to fourth grade math class -- there's something called "Order of Precedence" when it comes to doing calculations. One of the rules is that multiplication and division are performed before addition and subtraction, unless the numbers are grouped with parenthesis. The way the response above is written, the "Og - FG x 131.25 = ABV" implies the FG is multplied by 131.25 first.

This is basic math.

That was my point in my reply above -- where I got the obviously wrong answer of 'negative 131.5'. Far too many homebrewers blindly use formulas to prepare or understand their brew without understanding why we do what we do. My worry is that if we don't understand, then wrong information gets spread around.

Yes, we all understand we multiply the difference in gravities. We are somewhat experienced.

But what if we don't understand it, or don't have that experience? Someone reads "The formula is Og - FG x 131.25 = ABV", applies basic math rules, and gets the wrong answer.

The formula, as written, is incorrect.
Click to expand...

Stop being an ass. The formula was posted in good faith that anybody using it to determine % alcohol would have enough brain cells to rub together to figure out that -131.5% is not the correct answer and could infer that using the formula in the only other possible way would give a more correct answer. In most situations, yes, giving an incorrect formula could result in wildly incorrect results. In this situation anyone with a lick of sense realizes that the threshold for alcohol content in (most) beers/ciders will be more than 0 and less than 20. If the expected alcohol content is going to be more than 20 then we're likely not dealing with a novice here.

You're making it harder than it needs to be. Why would anyone need to account for the atomic weight of CO2 or any other minor variation? We're going to round the final value to a tenth of a percent anyway. Hell, I round to the nearest whole number, personally.
 
So I've just been able to find tables on PA from the books. Haven't found a calculation. I'm going to go with either just use a table on the ABV depending on the SG or use a calculator online.
 
Because we're trying to be the best brewers we can be.

And if we can't identify at least *why* we do what we do, then we simply don't know what we're doing.

I'm not saying we need to know the ins and outs of the chemical and biological processes we're working with, but we do need to have a broad, general understanding of what's going on and why we do it. Otherwise, it becomes magic and hand-waving and praying to the gods of fermentation, instead of the science and art that it truly is.

There are rules-of-thumb and shortcuts, to be sure. ABV calculation is one of them. But simply giving the " (OG-FG) x 131.3 = ABV " magic spell neither increases knowledge nor helps anyone become a better brewer.
 
geneb said:
Stop being an ass.
Click to expand...

Hear hear!

I mean really, does understanding the exact method for figuring out your ABV really make you a better brewer? No, not really. I know some awesome brewers that never even take measurements after fermentation. It's not about the science, it's about the process. Sure, science can help you nail down a problem in your process, but it is a means to an end, not the end itself.

This is so way off topic that I think I am done here now...
 
Fionnbharr said:
Because we're trying to be the best brewers we can be.

And if we can't identify at least *why* we do what we do, then we simply don't know what we're doing.

I'm not saying we need to know the ins and outs of the chemical and biological processes we're working with, but we do need to have a broad, general understanding of what's going on and why we do it. Otherwise, it becomes magic and hand-waving and praying to the gods of fermentation, instead of the science and art that it truly is.

There are rules-of-thumb and shortcuts, to be sure. ABV calculation is one of them. But simply giving the " (OG-FG) x 131.3 = ABV " magic spell neither increases knowledge nor helps anyone become a better brewer.
Click to expand...

I disagree with that knowledge making anyone a better brewer.

Knowing how we achieve the OG or FG does, yes. Knowing how and why grain and water create wort does. Knowing how and why yeast make wort into beer or how they make juice in cider does. But knowing the intricacies of how we determine the amount of alcohol in a brew? How does that make anyone a better brewer?

It's the yeast's job to make alcohol, not mine. I don't feel a need to micromanage (no pun intended) them. The only reason I would ever try to determine how much alcohol is in a brew would be so that, if I am asked, I don't have to say "I don't know".

I'm not a chemist, I'm a brewer. As for the "(OG-FG) x 131.25 = ABV" equation, I am willing to take it on faith that someone who is a chemist determined or at least verified this value. It may not be exact but it is more than exact for my needs.


ETA: lordbeermestrength is right.. We're way off topic here. If anyone wants to continue the conversation we should take it to a new thread in the Fermentation & Yeast, General Techniques, or General Beer Discussion forums.
 
One last post: I would like to show the world the fearsome science that Fionnbharr prostrates himself before.

BEHOLD!

The "unscientific" calculation: (1.06-1.05) * 131.25 = 6.565% =~ 6.6%

The "scientific" calculation, where EtOHm= molar mass of ethanol, CO2m = molar mass of CO2, and EtOHd = density of ethanol in liquid form: (((OG-FG)*(EtOHm/CO2m))/FG)/EtOHd

==>

(.05) * (46.07/44.01) * (1.01/.79)

==>

0.06691 or 6.691% =~6.7%


WOW!!!! .1% difference! This will surely make my beer taste like the nectar of the gods, the dead will rise and the blind will see!!

PRAISE SCIENCE!!!



EDIT:
My science calculations were off: The actual answer is 6.56%. SCIENCE BE GLORIFIED!!
[(.05)*(1.0468)/1.01]/.79 = 6.56%
 
Regardless, the formula to figure ABV is in every beer and wine brewing book that I and everyone else owns.
 
geneb said:
Stop being an ass. The formula was posted in good faith that anybody using it to determine % alcohol would have enough brain cells to rub together to figure out that -131.5% is not the correct answer and could infer that using the formula in the only other possible way would give a more correct answer. In most situations, yes, giving an incorrect formula could result in wildly incorrect results. In this situation anyone with a lick of sense realizes that the threshold for alcohol content in (most) beers/ciders will be more than 0 and less than 20. If the expected alcohol content is going to be more than 20 then we're likely not dealing with a novice here.

You're making it harder than it needs to be. Why would anyone need to account for the atomic weight of CO2 or any other minor variation? We're going to round the final value to a tenth of a percent anyway. Hell, I round to the nearest whole number, personally.
Click to expand...
total with you on this repl:ban:y
 
I learned from an old shiner that you go by the percent scale for approx. alcohol and the S.G. scale tells you when to get it out of the primary to prevent a dead yeast taste. He said the other scales are for Science guys. On your first read it should be 10+% and when its good to go it should down as close to zero if you start at 10% and its now at 5% you got 5% in that batch.
He may be wrong but his apple peach whiskey would make you talk to trees!
 
oldmate said:
So I'm taking it that no-one read the article I posted?
Click to expand...
I wrote it back in 2009. Does that count? It's been appreciably butchered since then but there is still a lot of basic truth in it. Clearly the amount of ethanol produced depends on how much sugar is consumed but not all sugar consumed gets turned into ethanol and not all the sugar in a wort or must gets consumed. Thus the best we can do is try to estimate how much actually gets consumed which we do by measuring gravities and estimate how much of that goes to biomass production. The rest we assume goes to alcohol. We eventually come down to a bunch of formulas, determined empirically, most of which simply multiply the apparent attenuation (difference between original and final extract readings) by a number. A refinement recognizes that the multiplicative factor is dependent on the original extract.

WRT the Wikipedia article, please note that it discusses beer. While the beer formulas are probably generally accurate enough to give at least a rough idea as to the alcoholic strength of wines and ciders I am sure those industries have developed formulae more applicable to those beverages. To accurately determine alcohol content one really has to go to the lab and measure. For beer and cider this is tough as the alcohol content is relatively low. With wine and mead it is a little easier as their alcoholic strength is greater.
 

Similar threads

P
Cell count estimation
Replies
8
Views
331
hottpeper13
H
Thomas1999
Not Fermentable Malts
Replies
24
Views
1K
Yooper
Yooper
Chalkyt
A “new” way to produce sweeter cider, perhaps.
2
Replies
41
Views
2K
Johnny2
J
X
Is there a difference in the formula for calculating titratable acid in wine and mead?
Replies
1
Views
281
lumpher
lumpher
P
Next steps
Replies
9
Views
655
Chalkyt
Chalkyt

Latest posts

Back
Top