Standard vs Alternate ABV

[Maxonian]

Hi everyone, I’m interested to see what formula everyone uses to calculate your ABVs.

When I wrote my recipes by hand I used the standard method for simplicity and carried on using it when I switched to the Brewer’s Friend app. Since the app calculates it for you, I’m wondering if I should be using the alternate method. I’ve been brewing a lot of high gravity beers recently and I think I may have been underselling the potency of them by using standard instead of alternate.

 

[An Ankoù]

I could never figure this one out. One would have thought that the abv calculators were based on the results some kind of formal chemical analysis of a range of samples so I never understood why there were two. I, too, use the standard one.

 

[Scottyburto]

I use
(OG-FG) x 0.129 = ABV

Is this incorrect?
Can't remember where I got it from.

 

[Maxonian]

I’ve always used (FG - OG) x 131.25. There doesn’t appear to be much difference in the final ABVs until your OG gets above 1.060. With super high gravities of 1.090+ then there’s a fair bit of difference but I’ve read that with these beers then the alternate method is more accurate.

 

[Maxonian]

I could never figure this one out. One would have thought that the abv calculators were based on the results some kind of formal chemical analysis of a range of samples so I never understood why there were two. I, too, use the standard one.

I just read a very technical article about ABV calculations which really made my head hurt.

 

[NotSure]

Using a formula beyond the simple ABV formula really doesn't make much of a difference until you get really high ABV as others have stated. The Hall paper is the formula I use for my website and other websites use it too. The advanced formula in Brewer's Friend do use the Hall paper, but they use a simplified version of Balling's equation plugged into the advanced equation. This will give a result that's too high. My site Calculator for Alcohol By Volume (ABV) and Attenuation (brewingcalculators.com) and Homebrew Dad's Alcohol by Volume Calculator (brewunited.com) do it correctly... or at least I hope!

 

[Maxonian]

Using a formula beyond the simple ABV formula really doesn't make much of a difference until you get really high ABV as others have stated. The Hall paper is the formula I use for my website and other websites use it too. The advanced formula in Brewer's Friend do use the Hall paper, but they use a simplified version of Balling's equation plugged into the advanced equation. This will give a result that's too high. My site Calculator for Alcohol By Volume (ABV) and Attenuation (brewingcalculators.com) and Homebrew Dad's Alcohol by Volume Calculator (brewunited.com) do it correctly... or at least I hope!

Thanks for sharing these. Do commercial brewers use the Hall paper too?

 

[NotSure]

Thanks for sharing these. Do commercial brewers use the Hall paper too?

I'm not sure (no pun intended), but I wouldn't see why not.

 

[Clint]

I'm not bothered. I only use the forum calculator.

 

[Jim Brewster]

I would assume of the two calculation methods, standard one is simplified and gives an error, although mostly insignificant within the normal range but will start to deviate at higher ABV, and the alternative method takes into account non-linearity with a correction factor and so gives a more accurate result beyond the normal range.

 

[Rodcx500z]

when i get a wobble on after 2 or 3 i know it's high abv

 

[Jim Brewster]

Purely out of acsdemic interest I plotted the two at an example 75% attenuation to see how the two formulas vary.

Standard (OG-FG)*131.25

Alternative (OG-FG)*67.1 * (1.775-OG)/(FG/0.794)

They're about the same up to 5% then the standard one gradually deviates..

Personally I just use the recipe as an estimate ABV and that's all, a bit lazy but I don't really feel it necessary and I prefer to keep things as simple as possible. The hydrometer has only been out of its case a couple of times.

 

[Scottyburto]

I use
(OG-FG) x 0.129 = ABV

Is this incorrect?
Can't remember where I got it from.

After a little Google turns out this is the calculation HMRC use, just incase anyone else was interested.
It's obviously not the most accurate as they allow a 0.5% variance for "tax dodging" Multinational Breweries!

 

[An Ankoù]

Standard (FG-OG)*131.25

Wouldn't that result in a negative value?

 

[NotSure]

Wouldn't that result in a negative value?

I'm guessing the HMRC won't let you use that equation for the tax calculations then

 

[Buffers brewery]

https://www.legislation.gov.uk/uksi/1996/1499/schedule/5/made
Beers up to 5.5%ABV have a +/-0.5% tolerance on ABV. Beers over 5.5%ABV have a +/-1.0% tolerance on ABV.

 

[Jim Brewster]

Wouldn't that result in a negative value?

Oh yeah, should have written them the other way around! I took them from brewers friend but of course it should be OG-FG

 

[NotSure]

Oh yeah, should have written them the other way around! I took them from brewers friend but of course it should be OG-FG

No comment.

 

[Scottyburto]

https://www.legislation.gov.uk/uksi/1996/1499/schedule/5/made
Beers up to 5.5%ABV have a +/-0.5% tolerance on ABV. Beers over 5.5%ABV have a +/-1.0% tolerance on ABV.

https://www.google.com/amp/s/www.bbc.co.uk/news/amp/uk-41059610