"LG1111" wrote:
So this is the question: How can there be that much discrepancy between
TA and
pH? I can't see adding tartaric acid to a must that has a pH of 3.2.
There is no direct relation between TA (% acid) and pH (strength of the
acid) .
From the pH FAQ:
"pH is related to an acid's strength in wine, while the TA relates to the
amount of acid. Although interrelated, they are not the same thing. A
solution containing a specific quantity of a relatively weaker acid such as
malic acid will have a different (higher) pH than a solution containing the
same quantity of a stronger acid such as tartaric.
The pH of a solution is defined as the -log of the hydrogen ion. Given the
measurement is logarithmic in nature, a solution with a pH of 3.0 is ten
times stronger than a pH of 4.0. The total quantity of hydrogen and
hydroxyl ions is constant in a solution, as one increases the other
decreases. Acidic solutions contain more hydrogen ions than hydroxyl ions;
basic solutions contain more hydroxyl ions than hydrogen ions. A pH of 7 is
neutral (neither acid or base) as the concentration of hydrogen ions and
hydroxyl ions are equal at that point.
"Normally", if the TA is within the correct range, the pH will be as well.
But there are many cases where this is not true.
In your situation (pH 3.2-3.3, TA levels .50), it is likely that you have
proportionally less tartaric and higher malic and/or citric acid levels. If
you add tartaric to achieve your target acid level, you will bring the pH
way down. If you add malic, you will bring the pH down much less. On the
other hand, the tartaric component will be reduced during cold
stabilization, and the malic during malolactic fermentation. So I'm not sure
how you should handle this situation.
This was discussed in (heated) detail in the following thread:
http://groups.google.com/groups?hl=e...e%2Bof%2Bph%2B
group:rec.crafts.winemaking%26hl%3Den%26lr%3D%26ie %3DUTF-8%26group%3Drec.cra
fts.winemaking%26selm%3D8003ada.0309161004.730dd78 e%2540posting.google.com%2
6rnum%3D1
The consensus that I got from the thread was to adjust the pH to the correct
level before fermentation, and don't worry about the TA. And adjust the
acid-level to taste post-fermentation.