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The most common way to calculate ABV (Alcohol By Volume) is through some correlation between Original Gravity (OG) and Final Gravity(FG).

Is there any way to calculate ABV just from the current specific gravity reading?

Example - a week into fermentation you can read an sg of 1.038. Is it possible to deduce the current ABV from this using just a hydrometer and as much fancy math as you can imagine?

  • presumably with two sg readings and a knowledge of the yeast's expected performance curve you could do something, but with only one sg reading it looks unlikely unless you had every other variable nailed down, and could assume exactly the same duration of lag phase etc. But then if you don't know the og, you don't have all the variables nailed down. – David Liam Clayton May 20 '18 at 18:36
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As Evil Zymurgist said, you can estimate OG and ABV based on uncorrected refractometer reading and final gravity, more precisely :

The formula is the following : calculation formula

Complete explanation can be found in : http://www.moundtop.com/alcohol/Alcohol-via-Refractometer-Hydrometer.pdf

which is based on the papers :

Rogerson, F. & Symington, C. (2006). A method for the estimation of alcohol in fortified wines using hydrometer Baumé and refractometer Brix. American Journal of Enology and Viticulture, 57, 486-490.

Son, H.S., Hong, Y.S., Park, W.M., Yu, M.A. & Lee, C.H. (2009). A novel approach for estimating sugar and alcohol concentrations in wines using refractometer and hydrometer. Journal of Food Science, 74, C106- C111.

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    This is great, actually the first time I've seen the formula layed out. I took a look at the brewzors source code, even as an ex programmer took one look at the 1000 characters of code and said F that, not even gonna try. Lol – Evil Zymurgist May 21 '18 at 13:33
  • The most accurate description I've seen to date - kudos, JeanMi! Is there a way to do this without a hydrometer, though? – Mike Meyers May 21 '18 at 13:56
  • With only 1 measuring device and 1 measure value, i don't think it is possible :/ (to my knowledge) – JeanMi May 21 '18 at 14:20
  • Damn.... Fair enough, was worth checking. Thanks! – Mike Meyers May 21 '18 at 17:37
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Actually there is a way to estimate the OG on finished beer. Then calculate ABV normally.

However it needs both a hydrometer reading and a refractometer reading, and some fancy math.

A couple programs have this formula built in.

Brewzor Calculator for free app Androids. Beer Smith for PC ( possibly in mobile versions IDK)

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