My understanding is the SG 1.000 is calibrated with distilled water at
20 degC (68 degF).

Zero PA (0PA) is a stable reference point, though it doesn't reflect the
true zero PA density of grape must. About 5-10 percent of the total
soluble solids in the grape must are from non-fermentable sugars,
organic acids, organic acid salts, nitrogen-containing compounds,
tannins, pectins and mineral salts.

These other soluble solids are responsible for a lot of the uncertainty
in PA calculation from must SG. Alcohol evaporation during fermentation
is the other significant variable making PA an inexact predictor of
final alcohol content.

I found the following reference about grape maturity useful for getting
a good picture of the grape growing practices and analyses on winemaking
results.
http://winegrapes.tamu.edu/grow/maturity.pdf

One topic they discuss is potential alcohol.

Gene



jim wrote:
Hi Gene, alcohol is definitely less dense than water, but if a wine at
1.000 is not quite dry, why do they calibrate 1.000 with 0PA? Do you
see why I think it is confusing?

Jim

On Nov 27, 9:34 am, gene wrote:
The final SG of a wine fermented to dryness has to account for the fact
that the alcohol in the wine is less dense than water. That's why the
dry wine has an SG less than 1.000. A wine at SG 1.000 is not quite dry.

Gene

jim wrote:
Heh sorry to miss you out. Thanks for the info.
I understand that PA starts with the potential. What I am getting at
is that SG and PA are given a common correlation as being discussed in
this thread. Yet, SG works on total movement (from initial to final
SG). So, what is the difference between a wine with PA of 15 that
finishes at SG 1.000 and a wine with a PA of 15 which finishes at
0.990?
That still *weirds me out* Many thanks and I hope this isn't too off
topic.
Jim
On Nov 27, 1:04 am, pp wrote:
Why is everybody calling me Joe these days? :-p
As for the 0.990 vs 1.000 difference, basically, you can think about
it as the table being designed so that instead of using the difference
between the starting and final sg points, you're only using the
starting point. In other words, the table is built with the assumption
that your wine ferments completely to dryness (because that's what PA
means) and gives you the PA values with that assumption.
Pp
On Nov 26, 1:37 pm, jim wrote:
I use this table:http://www.brsquared.org/wine/CalcInfo/HydSugAl.htm
which backs paul and joe's comments.
I have to admit though, I never quite understood how this can be if
0PA is 1.000 and I usually ferment down to around 0.990
Jim
On Nov 26, 8:36 pm, pp wrote:
On Nov 26, 11:46 am, "Paul E. Lehmann" wrote:
Joe Sallustio wrote:
Hi. Is there a special starter I should use to
re-start this? Room temperature shouldn't be
an issue - it's being kept in my pantry so it
is always warm enough.
Steve's post already gave you great advice and
the correct value of
'potential alcohol' for 1.100SG. (My tables
came from NBS so I know
they are right.) The only thing I would expand
on is the amount of
time to give it to get going. Starters need to
get going really well
before you add them to the total volume. I
keep doubling the volume of the starter and let
it get back to fermenting strongly.
13% ABV for an apple wine might be a little
heavy duty; if this died at around 9 or 10 % I
might be happy with that. I show that as 1.022
to 1.029 S.G.
bobdrob,
I show 1.115 as 19.3 % ABV; I have the book at
home that probably
takes them higher; I have spreadsheet I made on
my work PC. I can email you the spreadsheet.
Joe
Joe, are you sure of that? I quick check on my
program shows 1.115 SG to be equivalent to 15.78
Brix and the PA to be 15.78- Hide quoted text -
- Show quoted text -
Same here - don't have the tables on me but last couple of years we
got some Zin and Petite Sirah grapes that were over 1.130. I remember
checking the PA on those and even that was definitely under 20% - not
that we fermented them that way!
Pp- Hide quoted text -
- Show quoted text -