From "Winery Technology and Operations", by Dr. Yair Margalit, page 3:

% Sugar (w/v) = (Brix - 2.1) * density
Each 1.7% sugar (w/v) = 1% alcohol (v/v)

so, %Alcohol (v/v) = 0.58 * (Brix - 2.1) * density

where (v/v) is "volume per volume"
and (w/v) is "weight per volume"

with some cautions about the valid range of these relationships (stated on page 4), he continues:

"Thus, for example a must with 22.7 Brix and density of 1.095 has a potential alcohol of 13.3 +/- 0.2%"

Later on page 4, he shows a graph which expresses a linear relationship between Brix and density
and has the following endpoints:

Vertical axis (y) is Brix, horizontal axis (x) is density

Left endpoint (x = 1.05, y = 12.5)
Right Endpoint (x = 1.12, y = 28.1)


Here ends the paraphrase of Dr. Margalit's book...


Personally, I'm a bit confused about the equations on page 3 and the graph on page 4. The
equations alone would suggest that density and Brix are independent, but the graph shows
that they are dependent (which is what I expected). From the data on the graph, we might
be able to derive:

((Brix - 12.5) / 223) + 1.05 = density

and substituting into the first equation, we get:

% Alcohol = (0.58) * (Brix - 2.1) * (((Brix - 12.5) / 223) + 1.05)

Reworking (with liberal rounding), yields:

0.003Brix**2 + 0.54Brix - 0.06 = % Alcohol

which for Brix = 22.7, this yields 13.8%

So, my Algebra needs some work, but it's in the ballpark. Of course, this
assumes all the relationships are valid, which they might not be; I'm just
playing with the formulas, but I don't fully understand them yet. This equation
suggests a "rule of thumb" of "%alcohol is 60% of the brix", that might not
be close enough to be useful (or maybe just dangerous).

By the way, this is all at 20 degrees Celsius. And the book has commentary
on the use and temperature correction of refractometers
(see page 155 and 156).

I hope this helps. If not, let me know (I'd hate to start spreading bad "facts").
And if I've gone off the deep end with an invalid analysis, please point that out.


Jeff Griffith


PS the complete citation is:

"Winery Technology and Operations: A Handbook for Small Wineries", Revised Edition
by Dr Yair Margalit
Copyright 1996, reprinted 2003
published by "The Wine Appreciation Guild", San Francisco, CA

"Wade and Sheri" <wadesheri@charter.net> wrote in message news:vljq5jbdbu30fc@corp.supernews.com...[color=blue]
> Curious if anyone knows of a conversion formula from Brix to gravity? I
> bought a refractometer and have yet to find a good conversion. Or, if anyone
> knows how to calculate alcohol content just using Brix.
>
> Thanks, Wade
>
>[/color]