I'm embarrassed that every year I have the same question, and it still doesn't
make sense.

The grapes that I can get here on the east coast are usually overripe Central
Valley California grapes. Invariably, they have low acid levels. But I just
tested a sauvignon blanc batch that had pH levels in the 3.2-3.3 range (tested
with 2 different recently calibrated meters) and TA levels in the .50 range. I
tested the TA's on freshly pressed juice, using a titration method with a color
indicator. I even verified the titration using the pH meter and waiting for a
pH of 8.2 as the titration progressed, and the TA of .50 is valid. I guess my
NaOH standard could be off, but I doubt it.

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.

What would you do?

Lee

Lee,
You are not far off from my numbers on Central Valley juice from
Regina. I did a little experiment this morning on pH that you might
find interesting.

I have a blend of 12 gallons of Cab Sauv juice, 6 of Cab Franc juice
and 5 gallons of Cab Sauv grapes, pressed after about 5 days of
fermentation on the skins.

The SG is 0.996, it is still 'gassy'.

I checked the pH without removing the CO2, it was 3.65. After a few
second boil, it dropped to 3.55. Not a huge change, but significant
to me.

3 other blends of different juices did about the same thing, all read
a little different but the change was about -0.10 pH units.

Here is the initial and final pH and TA of a white (Riesling)from the
Central Valley this year.

Initial Current (3 weeks)
pH 3.17 3.10

T.A. 5.3 (corrected to 5.8 preferment), now 7.7.

Other reds did about the same. All went up at least 1 g/l. All taste
a little tart and will go through a cold stabilization which should
drop out some tartaric, so I'm pretty much not concerned here.

In other words, I'm not sure you have to add any acid, my Riesling TA
went up almost 2 g/l. If I added anything, it would be tartaric if it
were mine, it can be dropped out with cold stabilization.

Hope that helps.
Regards,
Joe


The grapes that I can get here on the east coast are usually overripe Central
Valley California grapes. Invariably, they have low acid levels. But I just
tested a sauvignon blanc batch that had pH levels in the 3.2-3.3 range (tested
with 2 different recently calibrated meters) and TA levels in the .50 range. I
tested the TA's on freshly pressed juice, using a titration method with a color
indicator. I even verified the titration using the pH meter and waiting for a
pH of 8.2 as the titration progressed, and the TA of .50 is valid. I guess my
NaOH standard could be off, but I doubt it.

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.

What would you do?

Lee

..

I checked the pH without removing the CO2, it was 3.65. After a few
second boil, it dropped to 3.55. Not a huge change, but significant
to me.


That would be significant to me Joe.

Wouldn't you expect the pH to go up after removing carbonic acid?

clyde

"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.

"LG1111" wrote in message
...
I'm embarrassed that every year I have the same question, and it still
doesn't
make sense.

The grapes that I can get here on the east coast are usually overripe
Central
Valley California grapes. Invariably, they have low acid levels. But I
just
tested a sauvignon blanc batch that had pH levels in the 3.2-3.3 range
(tested
with 2 different recently calibrated meters) and TA levels in the .50
range. I
tested the TA's on freshly pressed juice, using a titration method with a
color
indicator. I even verified the titration using the pH meter and waiting
for a
pH of 8.2 as the titration progressed, and the TA of .50 is valid. I
guess my
NaOH standard could be off, but I doubt it.

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.

What would you do?

I'd leave it as is and ferment it. Trust the pH. Ignore the TA. Sounds
like the grapes are low in potassium.

Tom S

Clyde,
I thought that was what it should do too, but that's why I measured
it. I made fresh buffers last night and am going to do it again on a
larger sample of wines; I have 8 going now.

It's a potential measurement from the probe to solution; maybe the CO2
gas that forms on the pH electrode confuses it, I don't know.

I'm an electronics guy, not a chemist though. Maybe someone else can
chime in that understands this better.

Regards,
Joe


"Clyde Gill" wrote in message ...
.

I checked the pH without removing the CO2, it was 3.65. After a few
second boil, it dropped to 3.55. Not a huge change, but significant
to me.


That would be significant to me Joe.

Wouldn't you expect the pH to go up after removing carbonic acid?

clyde