Greg Cook > wrote:

> I think the difference between pH 7 and 8.2
> during the titration is a matter of just a few drops anyway (the titration
> curve is very very steep at the point of neutralization of the acids).

Theoretically, that's true and I always assumed there'd be little
difference. I haven't done enough comparisons to accurately judge, but
I actually just read a paper recently which suggests this difference
*is* significant.

In the paper [1], they compared the OIV method (titrate to pH 7.0, 50
ml wine) and the AOAC method (titrate to pH 8.2, 10 ml wine diluted
with water to 100 ml) for 30 wines. They found no significant
difference due to operative technique (i.e. the dilution and sample
sizes), but they did find a difference due to pH end-point. This
difference correlated to a TA difference of 0.6 g/l (as tartaric) for
reds and 0.5 g/l for whites. Well, I consider that significant.

BTW, if the standard was to titrate to the actual equivalence point
for wines, we'd all be titrating to pH's of around 10. In the purely
practical sense, I'm glad we have a standard at pH 7/8.2. Certainly
saves on the NaOH ;-)

Ben

[1] Darias-Martín, J. et al. (2003). Comparative study of methods for
determination of titrable acidity in wine. J. Food Composition and
Analysis 16, 555-562.