Author Topic: ABV Calculation Different to Other Calculators  (Read 3596 times)

Offline abcthomas

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ABV Calculation Different to Other Calculators
« on: July 06, 2020, 11:22:22 AM »
Hi all,

I know there a lot of posts about ABV calculation on here but none of them appear to be the same issue I'm having.
 
So I've been brewing with BS3 for a little while now (my exact version is 3.0.8 for Windows) but I've never actually double checked their ABV calculations against other calculators, which seems odd now that I think of it...

But I've just done some comparisons with a beer I'm currently fermenting and I've realised that both the estimated ABV from the recipe screen and the calculated ABV from the "Alcohol and Attenuation" tool give out a different value to every other calculator I can find online:

https://www.brewersfriend.com/abv-calculator/
https://homebrewsupply.com/abv-calculator/
https://www.hopsteiner.com/abv-calculator/
https://www.morebeer.com/content/abv_calculator

So that begs two questions; which is correct, BS3 or all of the other calculators? And why are the calculations different?

To give some real data here are two calculations from some recent beers:

Beer #1
OG 1.077
FG 1.017
BS3 ABV: 8.2%
Online calculators (standard equation) ABV: 7.88% (one of the calculators differs by 0.02%)

Beer #2
OG 1.102
FG 1.029
BS3 ABV: 9.9%
Online calculators (standard equation) ABV: 9.58% (one of the calculators differs by 0.02%)

Even the "alternate" method that some calculators offer are still different from BS3.

Offline BOB357

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Re: ABV Calculation Different to Other Calculators
« Reply #1 on: July 06, 2020, 01:23:09 PM »
How many of the other calculators require you to enter an extensive equipment profile? More importantly, have you created an accurate equipment profile in BeerSmith?  With Beersmith, you furnish a lot of the data and the software does the calculations. This allows you to tailor the program to fit your equipment and procedure. Many of the freeware calculators assume some generic equipment and process with whatever efficiency fits their model.
Bob

Offline Oginme

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Re: ABV Calculation Different to Other Calculators
« Reply #2 on: July 06, 2020, 01:55:16 PM »
Most calculators use a simplified formula for calculation of ABV which is (OG - FG) * 131.25 = %ABV.

The actual calculation is a bit more complex and is described in the paper:  Examination of the Relationships Between Original, Real and Apparent Extracts, and Alcohol in Pilot Plant and Commercially Produced Beers published by Anthony J. Cutaia, Anna-Jean Reid and R. Alex Speers in the Journal of the Institute of Brewing.

Calculating ABV from specific gravity
The standard method of estimating ABV is to use the specific gravity. Specific gravity is the relative density of a liquid compared with the density of water. When fermentation occurs, the specific gravity of the liquid changes. You can monitor this change to find the alcohol content of your homebrew.

All formulas for finding the ABV are approximate, as they are found empirically rather than derived. The most recent formula was derived by Cutaia, Reid and Speers in 2009. The first formula from their research relates the measurements of the alcohol content by weight with the original and apparent extract:

ABW =(0.372 + 0.00357 * OE) * (OE - AE)

where:

ABW is the alcohol by weight, measured in percents
OE is the original extract (before fermentation), measured in Plato degrees (?P)
AE is the apparent extract (after fermentation), measured in Plato degrees (?P)
From this alcohol formula, they derived an equation for alcohol by volume:

ABV = ABW * (1.308 * 10^-5 + 3.868 * 10^-3 * AE + 1.275 * 10^-5 * AE^2 + 6.3 * 10^-8 * AE^3 + 1) / 0.7907

The last thing our beer calculator does is finding the exact amount of alcohol in a given volume of alcoholic beverage. For example, you can determine the volume of alcohol in a 500 ml bottle of 4.5% beer. If you are interested in finding this value, use this equation:

alcohol volume = total volume * ABV

Using this calculation, I got the following results based upon your posted examples:

Example 1:  OG 1.077 > FG: 1.017  ==> 8.08%   (BS = 8.0%)

Example 2: OG 1.102 > FG 1.029 ==> 10.08%  (BS = 9.9%)

Given rounding errors, this is not too far off the mark.

I also do not know what the other calculators are using for their computations.
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Offline BOB357

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Re: ABV Calculation Different to Other Calculators
« Reply #3 on: July 06, 2020, 05:02:35 PM »
Sorry if I misread your post and thought you were referring to calculations within the recipe design rather than the stand alone calculator.
Bob

Offline abcthomas

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Re: ABV Calculation Different to Other Calculators
« Reply #4 on: July 07, 2020, 08:23:40 AM »
Thanks for the in-depth response Oginme, I spent quite a few years as a 3D graphics programmer so these types of equations bring back fun(?) memories  ;D.

Your response prompted me to actually look into the equations and I didn't realise the amount of background and the different equations that were available.

I think the main thing to keep in mind is that all of these equations are approximate. Although from looking at the different formulas it looks like BS3 is using the CJJ Berry (1987) method: (SG-FG) / 0.00736

When plugging the numbers from both beers into that equation the numbers match exactly what BS3 outputs. Maybe a potential improvement to BS3 would be to allow the user to switch between the different equation methods when using the calculator.

The friend that I brew with actually works in a commercial brewery so we're going to test the ABV of beer #2 after fermentation. Should be interesting to see which equation was most accurate.

Cheers! 

Offline MartinFa

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Re: ABV Calculation Different to Other Calculators
« Reply #5 on: December 22, 2020, 05:36:12 AM »
I *think* BS3 is using the formula...

%ABV = 133*(OG-FG)/FG

which gives the same results as the Standard ABV calculator at https://www.brewersfriend.com/abv-calculator/

Offline jomebrew

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Re: ABV Calculation Different to Other Calculators
« Reply #6 on: December 22, 2020, 10:07:39 AM »
I created a web calculator over 10 years ago.  I see the formula I used in other calculators. Some are oddly almost the same exact javascript I wrote. weird.

My tool is at http://web.jomebrew.com/beercalc.htm where I used formulas from a long gone site primatetab. I saved a copy of their page for reference http://web.jomebrew.com/beercalc_primetabFormulas.html

To calculate ABV, I researched how ABV was calculated based on OG and FG and settled on ABV = ((OG - FG)  / 0.75)*100 which also approximates the ABV somewhere in the middle of formulas I found at the time. 

For SG and FG of 1.077 and 1.017, I calculate 8%ABV
For SG and FG of 1.102 and 1.029, I calculate 9.73%ABV

Ultimately, we are all estimating and using slightly different formulas and with different levels of accuracy.  Many commercial breweries use one of these formulas to report their beer ABV. They are allowed .5% variance from the actual ABV.

Offline meszibalu

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Re: ABV Calculation Different to Other Calculators
« Reply #7 on: December 28, 2020, 07:50:22 AM »
All formulas for finding the ABV are approximate, as they are found empirically rather than derived. The most recent formula was derived by Cutaia, Reid and Speers in 2009. The first formula from their research relates the measurements of the alcohol content by weight with the original and apparent extract:

ABW =(0.372 + 0.00357 * OE) * (OE - AE)

Hey Oginme, where did you find this formula? The publication what you refer (and available here: https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.2009.tb00387.x) uses another formula:
Code: [Select]
ABW = 0.387 * (OE - AE) + 0.00307 * (OE - AE)^2
Your formula is not the same, because the second one has AE^2 tags.

You also say:
ABV = ABW * (1.308 * 10^-5 + 3.868 * 10^-3 * AE + 1.275 * 10^-5 * AE^2 + 6.3 * 10^-8 * AE^3 + 1) / 0.7907

How did you arrive to this formula? The previously mentioned publication uses:
Code: [Select]
ABW = ABV * 0.7907 / SG
Where SG is the final plato converted to Specific Gravity.

Thanks in advance!

Offline KB

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Re: ABV Calculation Different to Other Calculators
« Reply #8 on: January 01, 2021, 01:41:07 PM »
Topic is interesting to me as I've run into different calculated ABV values between the recipe and the ABV tool over the years.

 

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