It is widely known that when you leave wine in a pertially opened btl, it starts to oxidize, with one of the prime oxidations being oxygen acting on ethanol to produce Acetaldehyde. Acetaldehyde is the primary sensory component you get in baked sherries and Madeiras. Yet you can leave a btl of vodka or gin open for several yrs w/o the formation of Acetaldehyde.
So...why is the production of Acetaldehyde occur in wine but not in spirits???
TomHill

But I'd guess that it's the distillation process. Spirits really aren't alive like wine is, and don't seem to change much with aging in the bottle or with exposure to air.

Right you are, Marshall...you ain't no chemist. But thanks anyway for giving it a shot.
The only wine I have that's alive are my Coturris....and they're teeming w/ all sorts of bugs that are truly "alive". But most of my wines, I hope, are not "alive". They may be changing as various chemical reactions are taking place, but I hope they're not bioligically "alive", save the occasional brettanomyces.
When one of those no-good/ornery/wascally oxygen atoms starts to attack an ethanol molecule to make an acetaldehyde molecule, I'm pretty sure it doesn't first ask that poor ethanol molecule if it had been badly abused in its childhood by that nasty distillation process. It just sees an ethanol molecule sitting there in solution and goes to work on it.
Bear in mind I ain't no chemist, ethier...just a simple little ole Country computational physicist.
Tom

From what I have read the oxidation of phenols to quinones in the presence of S02 allows some alcohol to be converted to acetaldehyde.
Alcohol doesn't easily convert to acetaldhyde without an enzyme such as alcohol dehydrogenase or other oxidative compounds to cause the oxidation.
Therefore vodka doesn't convert to acetaldehyde because it is only alcohol and water.

Here is a link.
http://www.newworldwinemaker.com/article_content.asp?id=228

A Google search of "phenol quinone oxidation acetaldehyde" will find other articles.

Gordon

Thanks, Gordon. That's what have been able to glean from other sources as well. It's not a simple matter of an oxygen molecule knocking up an ethanol molecule to produce the offspring acetaldehyde, but there are other complicated reactions, some that include hydrogen peroxide, that do the nasty job.
Tom

Tom, good question, and a nice reference in answer from Gordon. EtOH on its own, as you noted, is very stable. I've had some opened vodka bottles as old as 30 years that were just fine, even cognac opened 10-15 years tastes pretty good. I think two things are at play: wines contain the phenolic compounds Gordon's article talks about; any spirit may or may not (probably not), but I think the key is that the spirit has already been well cooked by virtue of the distillation process. So, there's probably not much there aside from alcohol, water, and some very low concentration compounds that make the spirit what it is, and anything that is there has already reacted through distillation.

Cheers,
Alan

Ok now remember that when I took my first chemistry class the periodic table was an X with only dirt, air, fire and water as elements. I understand that they have discovered others since then.
However as I understand things ethonol is not easily oxidized but represents food (carbon) used to oxidize yeasts and bacteria that for on the surface ie as in Sherries. This oxidation also produce acidic acid and ethyl acetate which are very volitile and are noticable very quickly.
Also in higher alcohols solutions acetaldehyde tends to accumulate rather than oxidizing into acedic acid. (all redox reactions are pH dependent and I do not know what pH spirits tend to be but this may have an effect.
The vodka in question my well be producing acetaldehyde but may not have the necessary componants (that are in wine but not spirits) to create the more volatile and noticable oxidative components.

Now if you find that any of the above makes sense and helps perhaps you can help me. Please help me explain why whenever I take brix readings with a hydrometer, no mater how I do it or the what the phase of the moon is when the hydrometer slows down the side of the hydrometer with the brix scale always faces away from me. Now there is a question.

Easy answer for that one...it's the very same reason that when you drop your toast, it always lands jelly side down. Or when you stand near a bonfire, the wind is always blowing the smoke onto you...no matter which side of the fire you stand. It's just nature.
Thanks for your chemistry lesson, Joel. Your explanation is pretty much what I've found from other sources. It's a complex reaction that produces the acetaldehyde, not just a simple oxygen atom attacking an ethanol molecule. The necessary phenolics to carry this out are present in wine, but not in spirits. Still don't fully understand it in detail, but have the general picture, though.
Tom