Calculating abv

[mark1964]

Can anyone help with calculating abv pre ferment. I've forgot how to do it

[guypettigrew]

It's about 10% of the OG. In other words, a wort of 1.050 will give you a beer of about 5%, probably a bit less.

Graham Wheeler's beer engine will give you a more exact figure, but is all depends on the finishing gravity. You can find it on this page.

Guy

[mark1964]

Thanks

[richard080561]

There's an easy to use calculator on Brewer's Friend, you enter the SG and OG .

[nickjdavis]

OG minus SG times 131 will get you pretty much as close as you need to be.

e.g.

1.050 - 1.010 = 0.040

0.040 * 131 = 5.24 (%)

[vacant]

Plus any priming sugar.

100g in 23 ltr converts to CO2 plus alcohol adding about 0.5%.

[Kev888]

As above, you can guess it based on the difference between apparent OG and predicted FG, plus any priming. The FG can obviously vary quite a lot, depending on the type of yeast and fermentability of the wort, so the accuracy of the ABV prediction will depend on how closely you can predict the FG. Thats something I'm not brilliant at with new recipes/brews, I can often be a percent or so out unless I've tested them before or done a forced-ferment.

(Once you have the actual FG then there are more detailed formulae, that would be accepted for duty calculations. It is still a similar principle, but the values change slightly according to different OG ranges and so on).