Alcohol calculator for the lazy brewers amongst us (like me)

[Ady1975]

Why bother with mental arithmatic?

http://www.cascadehomebrew.com.au/brewk ... lators.asp

It's a nice little site to spend some time browsing aswell to be honest, some good tips for new brewers like myself.

[Eadweard]

It doesn't calculate correctly though. For normal strenth beer for each degree fermented you get 0.129% alcohol, the online calculator gives me higher than that.

[Ady1975]

oh, sorry, maybe no good then, I didn't know. Just assumed it'd be right. damm those hoodwinking aussies!!
Having said that, I invented a couple of figures and I checked the results from the site against the calculation method given in my coopers instructions and it was very slightly less.

I just don't know who to trust now!!


on the plus side, everyone will think they're brewing strong beer and be amazed at how well they can handle it !!

Sod it! Drink it!

[Sunray11A]

Maybe you'd like to try this one:

http://www.worldwidemetric.com/metcal.htm

[anomalous_result]

It doesn't calculate correctly though. For normal strenth beer for each degree fermented you get 0.129% alcohol, the online calculator gives me higher than that.

Honestly, I've seen more numbers touted as correct than I've had hot dinners. Divide the number of degrees fermented by anything between 7 and 8.1 and you won't be far off.

[Eadweard]

Well, the method I use is the one HM revenue and customs use:

http://customs.hmrc.gov.uk/channelsPort ... 402_149026

[nik_g]

Out of interest, does anyone know where the various constants come from? Are they determined analytically or experimentally?

Or, judging by the range of values out there, just plucked out the air?

[Lillywhite]

7.45 is the Gay-Lussac constant...so far it's the only one with a name so it must be right

Out of interest do you need to add for the priming sugar or is that included in the 7.45 figure?

[nik_g]

Interesting - after a bit of googling on Gay-Lussac (thanks for the name Chris!) I see that the true value of the 'constant' is dependent on the FG (as suggested on the HMRC page). The actual calculation, derived from the explanation given here, is:

ABV(%) = (OG-FG)*105/(FG*0.79)

where gravity values are in kg/l (i.e. water would be 1.000, not 1000). So for the Coopers Stout I just kegged, OG 1.042 FG 1.014, the ABV would be 3.67% using this method, and 3.76% using (1042-1014)/7.45

Or, looking at it another way, the constant to be used with an FG of 1014 would be 7.63, based on the equation above. (Interestingly, this suggests that the 7.45 constant is only 100% accurate when applied to a brew with an FG of 0.990 - so maybe historically this constant came from wine makers?)

To be honest though, I suspect for most of us that such a small error (<0.1% in the example here) won't cause much lost sleep!

I'll stop boring you all now...

[Ady1975]

The Irony!
I posted this for Lazy brewers and everybody is out searching their chemistry books for exact figures and putting more effort in than ever.
I think i'll stick with the loosely accurate calculator and just tell my mates it's about 4-5%.

on a serious note, i'm off for a drink!

[nik_g]

It is unnecessarily complex when og-fg/7.45 gives perfectly good results considering the accuracy of your average hydromenter/refractometer

Agreed - I can't claim to be able to measure SG values with anything like the accuracy required for the precise value of the constant to be an issue. I was really just satisfying my curiosity as to where the value came from.