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 -
>