John Czerny asked about measuring acidity in a fermenting wine.
While my first reaction to this question would be why would you want or need to test/measure the acidity in a fermenting wine, the short answer is that there is no way to do this. Carbonation in the fermenting wine will skew any testing that you try to do. Even the winemaker’s testing of brix level to see how the fermentation is coming along will not be completely accurate but, in that case, the accuracy is not as important as the ability to track that the wine is indeed fermenting properly.
Acid testing should be done in the juice and then again in the finished wine.