[TheFruitlessPunch]

Hi everyone,

So basically my situation is... I've neutralised 20 ml of wine to ph 7 with 0.1M NaOH then I left it in the incubators at various temperatures for 5 days. pH unexpectedly went up to 7.6 for the 5 degree samples. pH dropped to 6.3 on once sample left at 35 degrees Celsius, but the other two sames went to 7.1 pH. The samples left at 45 and 55 degrees stayed around pH7. Problem is that I can't account for the pH level rises. The autoionisation of water was the best explanation, but I let the samples cool down to room temperature for about 2 hours before making my pH measurements with the pH meter.

I was skeptical so I did another experiment where I didn't neutralize the wine and just placed them in the incubators. And titrated the amount versus the control. Surprisingly, the titre amounts for the wine samples were all less than the control by about 0.3ml average which suggests that more base was formed in the wine. Completely opposite to the theory. So my big question is, what exactly happened or could've happened? I have accounted for many errors and still can't explain it. And the autoionisation of water occurs pretty fast according to wikipedia so I guess that won't be acceptable as an explanation.

I've even run a t-test and it showed that the pH did rise a bit and was not due to error by the pH meter.

None of the experimental data matches up with the oxidation of ethanol which is: Ethanol + oxygen ------> Acetaldehyde + oxygen -----> acetic acid + water
Which should cause pH to drop. But it didn't happen apparently. So I guess that the amount of acetic acid formed wasn't enough to change the pH?

Corks were left on all wine samples while they were in the incubators.]

I think that acetic acid did form and that the wine oxidised because I saw that the wine turned yellow at 55 degrees suggesting that it was oxidised and one sample went a bit hazy at 25 degrees. Perhaps there just wasn't enough oxygen in the flask for full oxidation and the reaction halted at acetaldehyde, but that still doesn't explain why more base formed as suggested by the pH and titre volumes.

I am so lost. I have done a lot of research into the mechanisms of wine oxidation and still can't find an answer that would explain my results. Any help is greatly appreciated.

Also my hypothesis was that, the acidity of wine will increase the most at optimal temperatures for bacterial growth, 25 degrees Celsius, and decrease as temperatures veer from 25 degrees.

[Arkcon]

Wow.  Lots of things are happening here.  I have only the most limited suggestions.  To start with, I'm afraid you need a lager sample.  Its just fine to do something in duplicate for added accuracy, but when your two samples a wide apart, then all bets are off.  Consider doing maybe 10 samples at your worst result, 35°C, to check your precision with all your manipulations.

Wine is a complex sample, with multiple sources of acid.  Consider a sort of dry run:  prepare a 10% ethanol in water sample, and see if that sort of sample behaves the way you expect at various temperatures and time points.

I have no idea where you're going with some of your missive.  The autoionization of water always happens, and accounts for water's slight conductivity.  It will never effect a titration or a pH meter.  Or at least, is always the case in every aqueous sample, so not something we have to worry about.

[Borek]

To start with, I'm afraid you need a lager sample.

That would be a completely different experiment (although beers do get sour with time) 

[Corribus]

To start with, I'm afraid you need a lager sample. 

Freudian slip?