More on TA Measurement

If I remember correctly, the 8.2 pH number comes from where phenolphthalein changes from colorless to pink.

FWIW, I haven't even bothered to measure TA on my wine/juice/must for the past 15 years or so. I watch the pH very carefully though. That's the number that really counts in the long term.

Tom S

Hi: The titration curve is very steep at pH7 so there is very little difference between 7 or 8.2. The latter is the accepted value/

phenolphthalein

Tom I, like you, have started to rely more on pH. I posted a question to the group a couple weeks ago but never got a response. The question is: Does the pH change once the wine is bottled? I assume it does because there are some chemical changes taking place during the aging process. I am just trying to get some handle on what is happening and how to possibly get longer shelf life from my wines. Typically, I have found that my red wines are best between 18 months and three years, but I have been keeping track of the pH of my unbottled wines recently and wonder if proper pH control before bottling could lengthen shelf life.

Tom,

I realize the importance of pH to the stability of the wine, particularly SO2 requirements but don't understand why you don't monitor TA as well. Everything I've read suggests that TA determines the acidity taste by 10 to 1 over pH. In the event of a must with the pH in the "normal" range and the TA much higher don't you risk a wine that is too acidic tastewise. For example, I now have a Riesling-Geisenheim blend that is almost fermented out and has a pH of 3.29 and a TA of 11.2 g/l which I think is too high so I'm inclined to lower the TA to at least 9.0 keeping in mind that I am making an off-dry wine.

Of course the taste-test is always important but it is difficult to sense the acidity by taste until it is fermented out somewhat.

I'd be interested in your thoughts particularly on the TA of my blend.

Cheers,

Glen Duff

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Tom S wrote:

From a pure chemistry standpoint, titration to pH=8.2 will yield the more "correct" value for TA. The reason is that wine is a buffered solution. When you titrate using NaOH, you are neutralizing the weak organic acids in the wine (Tartaric, Malic, Lactic, etc.) with a strong base, namely NaOH (Sodium Hydroxide). The result of this neutralization reaction is things like Sodium Tartrate, Sodium Malate, etc. These compounds are referred to as salts. A salt that is formed from a strong base and a weak acid will itself be slightly basic (pH>7.0), likewise, the salt of a weak base and a strong acid would be slightly acidic. During titration, you are neutralizing the weak acids and forming salts which are slightly basic. So, when you have neutralized all the organic acids in the wine by titration (which is the definition of determining Total Acid (TA)), all you have left is a bunch of salts of weak acid/strong base which are slightly basic and give a pH~8.2, slightly basic.

CHEERS!

phenolphthalein