... I hate computers sometimes...

Here is what I was saying before about potential alcohol;

Dujardin (1913):

PA (V/V)= 0.0594*[2.66*Oe-31.8]

Where Oe = Oechsle [(s.g.(20/20C-1.000]*1000

Ribereau-Gayon (1975):
PA (V/V)= 0.0595*[2560*((S.G 20/20 C)- 1)-22.2]

These two come out pretty close to one another.

Californian Data (Bioletti (Marsh 1958):

PA (V/V) = 0.592*[(sugar w/w%)-3.0] (Huge difference)

From Ough, Amerine and Jones (1963-1985)"
PA (V/V) a+b* brix

Where 'b' varies by year, cultivar and growing region and 'a' varies
from -4.92 to + 4.37. I can't give you what a and b are, they are
measured values that are not stated clearly (at least to me).

The bottom line is they saw mean ethanol yields vary from 0.665 to
0.588 from region I to region IV over 9 years. That's a variation on
the order of 1.5% varied around 12.5% V/V.

The modulus 145 values of Baume roughly correlate to PA if you exclude
nonsugar extract, a bad idea. The good news is its easy to measure
that one in finished wine, but by then its a little too late. You
could guesstimate at 2 or 3%, but that is what the other calculatins
are compensating for and they got those values from somewhere.


I guess what I'm trying to say is as far as i am concerned Potential
Alcohol is just a best guess. Too many factors can influence the
final yield of a wine. It's hard to estimate the unfermentable
dissolved solids and that will impact a hydrometer, period. That
number seems to bounce around at least 1 % that's a big deal to me.

As to the prefered methods of analysis, ebulliometry and distillation/
hydrometry are really the only approved methods of measuring alcohol
by the BATF. Ebulliometry is affected by sugar at 2% or greater,
distillation/ hydrometry are impacted by excess SO2 (>200 mg/L) and
excess acetic acid (>0.1%). As long as those issues are deal with,
you can get accurate data to at least 0.3% which is good enough for
BATF. (I can't speak to other countries regulations, I just don't
know for sure.)

I have a chart of ebulliometric values once barometric pressure is
compensated for from Wine Analysis and Production by Zoecklein et al
that I am going to transfer to Excel as an FYI.

Regards,
Joe