Any reason to use the alternate equation for higher abv beers? I get almost a full percentage point more using the alternate equation for a 1.093 og beer.
The relationship between change in real extract and alcohol just isn’t linear, it varies with original extract across all beers, no matter the gravity. But AFAIK it’s pretty simple to approximate: ABW=[0.8192(OE-AE)]/[2.0665-(0.010665OE)] That’s the formula I’ve always used for all beers. Is that what’s now called “alternate?” Is it the standard? Or is there another one out there now?
According to some sources:
Standard:
ABV = (og – fg) * 131.25
Alternate:
ABV =(76.08 * (og-fg) / (1.775-og)) * (fg / 0.794)
I get 9.3% abv with the standard and 10.1% abv with the alternate
Apparently the alternate may be more accurate for higher abv beers. I’m too dumb to know what is better or more accurate. One of my apps is standard and another appears to use the alternate. I guess I will just send it to the lab.
Well, that second one obviously accounts for difference in OG, and the first one just assumes a linear relationship. I’m way too lazy to figure out if the second is just a restatement of the one I know. But anything accounting for different OG would be more accurate for all beers, so if your calculator gives you a choice, why not always use the alternate?
I don’t know hence the post. Beersmith seems to use the standard equation from my experience.
It’s math time. I opened Excel and dropped the two formulas in with a range of original and final gravities. The OG values I used were 1.100, 1.090, 1.080, … down to 1.020. I set the final gravity for everything to be 1.000. Here are the ABV results:
Standard formula:
1.100 - 13.1
1.090 - 11.8
1.080 - 10.5
1.070 - 9.2
1.060 - 7.9
1.050 - 6.6
1.040 - 5.3
1.030 - 3.9
1.020 - 2.6
Alternate formula:
1.100 - 14.2
1.090 - 12.6
1.080 - 11.0
1.070 - 9.5
1.060 - 8.0
1.050 - 6.6
1.040 - 5.2
1.030 - 3.9
1.020 - 2.5
Assuming these equations are accurate, it looks like the standard would be good up through about 1.060. Once it gets up to 1.070 they start to split. I think as Robert stated, the alternate should be good to use all the time.
Thanks guys
Thanks, joe_meadmaker, for doing the math for us, the math-challenged and lazy. I still wonder if my weight/°P based formula is effectively the same as the alternate SG version given here. But I don’t wonder enough to actually do any math.
Robert, here’s the results from your equation. But take this with a grain of salt because there have been a lot of conversions with the numbers. I first found a website to convert the test gravity readings to OE and AE. I then also needed to convert the ABW results to ABV. For which I used a linear equation, even though the relationship isn’t linear. It was the only one I could find that gave results that made sense.
ABW=[0.8192(OE-AE)]/[2.0665-(0.010665OE)] converted to ABV:
1.100 - 13.5
1.090 - 12.1
1.080 - 10.7
1.070 - 9.4
1.060 - 7.9
1.050 - 6.6
1.040 - 5.3
1.030 - 3.9
1.020 - 2.6
So from that, the formula you have also appears to pull away from the standard as OG goes up, but not as much as the alternate formula. Who knows which one is actually more accurate? These equations are always advertised as an “approximate ABV” anyway. I think any of these are close enough at the homebrew level.
Now it’s time to RDWHAHB!
Yeah, the formula I have (Greg Noonan was my source a couple of decades ago, and I’m sure I saw the same in something by George Fix too) is definitely an approximation, I suspect precision requires a regression equation. What’s probably the key thing here is that the digression starts at the same point, and tracks closely, so I’d bet both equations are approximating the same “real” formula. And also, most importantly, it does suggest that up to a pretty high gravity, the inevitable errors in your gravity readings will be far more significant than the errors in your chosen calculator. Thanks again, cheers, enjoy your evening.
(In my equation things probably go pear shaped right off the top. That 0.8192 is an approximation of the relationship between real attenuation and apparent attenuation. Another nonlinear relationship, I believe. The SG equation is obviously doing the same, differently. )
I’m glad that some of you guys took classes in college that were where I stopped, or way beyond where I stopped. I trust your calculations and in no way suggest that I can follow them. I rarely care significantly what my final gravity is, but I appreciate that you guys do, and that is cool with me. Thanks for being the keepers of the gate, fellows!
Yes, it is important to calculate the ABV – Alcohol By Volume. Fans of highly alcoholic beers are well aware of what ABV means—or at least that a beer with an ABV above 10% has the potential to leave you with a buzz before the first pint’s finished. Determined with an instrument called a hydrometer. [abv calculator](http://abv calculator) is a handy one-stop tool for determining the final ABV percentage of your fermented beverages. To determine the ABV, simply measure the Original Gravity (OG) of your wort or must on the day you made it and then measure the FinaGravity (FG).
One of the greatest articles ever written on brewing calculations:
This article first acquainted me with many of the more thorough versions of common brewing calculations.
The relationship is non-linear. I learned almost 20 years ago that the 131.25 factor is a farce, that at low alcohol the factor is closer to 128 and at high alcohol it’s closer to 133 or 134. Forget the effing .25, that’s ridiculous. The result is good to 2 sig figs at best.
So… for a 1.093 beer finishing at approximately 1.023, just for example, I’d use a factor of 133, which by the old linear equation would give (1.093 - 1.023) * 133 = 9.3%. But maybe that factor should be 134. If so, then it’s 9.4%. Meanwhile…
I’d have a hard time believing any “alternate” equation that told me the ABV is >10% unless the FG was much lower than my example of 1.023.
Thanks for the link, Big Monk. Now I’ve got a refinement of the first term (approximation of RA) in my old equation (post #2.) So now I’ll go with ABW = [OE - (0.8114AE + 0.1886OE)] ÷ [2.0665 - 0.010665*OE]. Still an approximation but a better one.
(Edited for numerous bungles.)
Reread article, finally got the idea of that “q.” Now I think the really accurate equations have displaced my old approximation, and what I said above, in my memory. Thanks again.
Had some down time today and made myself a new spreadsheet. Incorporated the detailed equations from the Hall article, and the Novotný refractometer correction per his 2017 article. Now I have a comprehensive and very accurate alcohol and attenuation tool on my phone, tailored to my needs and practices. Proves two things: Zymurgy can be a valuable resource, and this forum is corrupting this old, curmudgeonly pencil, paper and wetware guy. 
I’ve been beating the drum on that article for years and all those calcs have lived in my spreadsheets for years.
I put this together as a companion for the article:
It’s a nice article posted out there. Haven’t seen such a good analysis of abv calculation for a while. When I was traveling throughout Europe I had participated in various alcohol drinking contests (ABV higher than 40%). And they had very stupid rules, so oversized people couldn’t even participate. You know, I’m not a skinny guy, so I had to convert kg to lbs proving that I can participate. It was insane, but I even won a couple of contests. Honestly, I’ve never drunk anything since that trip because I felt so bad these days.
By the way, If anyone knows other articles like that, pls share. It’d be interesting to compare the methodology of research and the conclusions in the end.