# Why is the titratable acidity of my wine going down as it ages and oxidises?

I am currently studying chemistry in grade 12 studies and I have come across a halt in my investigation.

The experiment was to see how the increase in ethanol would lead to a more acidic wine, because ethanol oxidises to ethanal and then to acetic acid. However, the inverse has appeared to happen throughout the 15 days of the test. Inbetween the tests, the wines were stored in an airtight bottle however they had a chance to oxidise while we opened them to test them.

Why is the acidity of the wine decreasing when the increase in reactants should also result in the bias towards the product side? My tests have yielded the opposite to what I expected (titratable acidity going down by almost half of what it was initially by the end of the 15 days) and I cannot explain it in my discussion.

• Have you considered esterification ? – Poutnik Jun 13 at 1:38
• @Poutnik I haven't learned about that, however i will google it and try to learn for myself. – Samuel Byrne Jun 13 at 1:44
• $$\ce{EtOH + R-COOH <=> R-COO-Et + H2O}$$ Typical esterification constant in water is 4, AFAIK. If you add ethanol to mixture previously in equilibrium, the concentration of organic acids would decrease ( in absence of oxygen demanding ethanol to acetic acid fermentation ) – Poutnik Jun 13 at 1:49
• @Poutnik Cheers, pretty sure that's what happened, I don't fully wrap my head around it but as long as the theory is there it should make sense in general. – Samuel Byrne Jun 14 at 1:52
• If you let wine and alcohol enriched wine open to air, then the later should be more acidic. But there may be the catch the alcohol concentration must not be too high, otherwise fermentation to vinegar may not run well. Note that it is rather metabolic then chemical process. – Poutnik Jun 14 at 4:28