Calculating ABV - Home Brew Forums

 Home Brew Forums > Calculating ABV

02-17-2011, 06:01 AM   #1
muse435

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So i have BeerAlchemy on my mac and a trial of Beer Smith on my PC. When i entered my last batch in to BS i got a different ABV than with BA. I tried a couple of online calculators and got some more ABVs

5.9 - rooftopbrew.net
5.78 - brewersfriend.com
5.74 - Beer Smith
5.9 - BeerAlchemy

Why am I getting a variety of different ABVs?
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02-17-2011, 06:36 AM   #2
RMitch
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Simple errors/variations in the programming of those "calculators". Best bet is to take an average of them all.

5.83% ABV

02-17-2011, 06:45 AM   #3
Weizenwerks
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OG-FG and multiply by 131.25.

02-17-2011, 01:14 PM   #4
SumnerH
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Quote:
 Originally Posted by Weizenwerks OG-FG and multiply by 131.25.
That's the simplified but less accurate formula; it underestimates slightly in the <7% ABV range and underestimates more significantly for bigger beers.

More accurate:
abw=76.08*(og-fg)/(1.775-og)
abv=abw*(fg/.794)

The Brewer's Friend site is using the simplified algorithm.

Rooftopbrew looks to be using the more accurate one (BeerAlchemy has the same answer so is presumably using the same algorithm).

BeerSmith must be using the simplified one and rounding things off too early in the process or something.
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02-17-2011, 01:20 PM   #5
trevorc13
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Quote:
 Originally Posted by Weizenwerks OG-FG and multiply by 131.25.
I'll have to remember this. Of course factoring for temp too. I adjusted my og by 1 point and my abv went from 7.87 to 8.0.
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Thanks for the input

02-17-2011, 03:40 PM   #6
Weizenwerks
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Quote:
 Originally Posted by SumnerH That's the simplified but less accurate formula; it underestimates slightly in the <7% ABV range and underestimates more significantly for bigger beers. More accurate: abw=76.08*(og-fg)/(1.775-og) abv=abw*(fg/.794) The Brewer's Friend site is using the simplified algorithm. Rooftopbrew looks to be using the more accurate one (BeerAlchemy has the same answer so is presumably using the same algorithm). BeerSmith must be using the simplified one and rounding things off too early in the process or something.
The simplified formula is good enough for home brewers that want an idea, but don't need much precision.

02-17-2011, 05:38 PM   #7
SumnerH
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Quote:
 Originally Posted by Weizenwerks The simplified formula is good enough for home brewers that want an idea, but don't need much precision.
Yep, but the poster was asking why different software was giving him different numbers. The answer is that 2 of them are using the more precise formula, one's using the simple formula, and one's doing something weird.

Not directed at you: if you're writing brewing software, why use the simple formula? The computer is good at doing math quickly...
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On deck: Little Bo Pils, Bretta Off Dead (Brett pale)
Secondary: Oude Bruin, Red Sky at Morning (Sour brown ale)
On tap: Saison Duphunk (sour), Amarillo Slim (IPA), Earl White (ginger/bergamot wit)
Bottled: Number 8 (Belgian Strong Dark Ale), Eternale (Barleywine), Ancho Villa (Ancho/pasilla/chocolate/cinnamon RIS), Oak smoked porter (1/2 maple bourbon oaked, 1/2 apple brandy oaked)

02-17-2011, 06:05 PM   #8
muse435

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After doing some more looking online i found that different require different formulas, I assume the reason why i kept getting different results is due to the fact that programmers are lazy and only wrote a single line of code for the calculations. I'm guessing that they used a medium value for F that will/should give a good approximation, with higher degrees of inaccuracy at the extremes.

As a result i'm now writing my own code based on the UK customs office definition of ABV. I'm not sure if it will be right but hey, its something to do at work
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02-17-2011, 07:08 PM   #9
frazier
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You know, after your third beer you're not going to care...
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02-17-2011, 07:29 PM   #10
muse435

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Quote:
 Originally Posted by frazier You know, after your third beer you're not going to care...
I'mnot neerly as think as u drunk i am
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