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"Ben Rotter" > wrote in message
om...
| 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.