So, the common belief is that wine ages in bottle because of oxygen transfer through the cork.
In sparkling wine this obviously doesn’t happen until the wine has gone completely flat. I know there are some very slow Maillard reactions going on in the wine, but what else changes in sparkling wine over time, specifically the first 30 or so years when there still should be some bubbles left.
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Why do you think air doesn’t get through the cork in champagne? It’s still cork, like any other wine.
I think he’s saying that the bottle is under pressure, so any air exchange should be going from the area of high pressure (inside the bottle) to the area of low pressure (outside the bottle), not vice versa.
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Yeah, that’s not how it works.
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Fascinating question. I’d never considered it before.
Can you enlighten me? How does it work?
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“The huge difference in CO2 partial pressure between the headspace (close to 6 bars at 12 °C) and the ambient air (around 0.0004 bar) forces CO2 molecules to slowly escape outside of the bottle, while at the same time O2 molecules invade the bottle (Liger-Belair, 2012, Valade et al., 2006)”
from Natural oxygenation of Champagne wine during ageing on lees: A metabolomics picture of hormesis
Gougon et al, Food Chemistry, 15 July 2016, Pages 207-215
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No time, will come back and answer later.
It’s common to think that because one component has a high partial pressure that it somehow prevents other gases from entering a solution - or in this case, permeating through the cork. But molecules are not walls, or pistons. They are tiny particles, circulating randomly in what is mostly empty space (at least in the gas phase; and in solution, they are spread out and separated by the solvent, in this case water and ethanol).
The way to think about this is like watching a large field of people walking around randomly, but with plenty of space between them. You could have a large number of people in red shirts, and a small number of people in black shirts. Even though the red shirts might be tending in one direction, the black shirts would have no problem passing right by them in the other direction.
You have to think about chemistry of this kind in terms of probability. That’s what governs the behavior of gases and solutions. Particles moving randomly, their behavior determined by probability. Things like “pressure” are just the bulk summation of these random probabilities.
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I learned this the hard way.
One of my “wine cellars” used to be a cold storage room that had suffered from water damage, ie. there was a somewhat noticeable, mouldy mildew smell in the air. I didn’t think much of it, just kept some of my wines and beers there.
At some point I noticed that all the beers I had aged there for a prolonged time had a noticeable mildew aroma in the nose. At first I thought some of the beers were just faulty, but after a few bottles I could see a trend - the longer the beer had stayed there, the more noticeable the moldy nose.
I had thought this was impossible - the high pressure inside the bottle should’ve kept unwanted aroma molecules out! However, I came to the conclusion that the crown cap might keep the CO2 inside the bottle, but if the liner is permeable to the aroma molecules, they will slowly diffuse through it from where the density gradient is higher (air) into where it is lower (inside the bottle).
One of my friends who worked as a chemist at a brewery told me that it would be impossible for a beer to pick up moldy smells just by aging it in a cellar that smells moldy. I opened one bottle for him as all he said was something along the lines of “Well I’ll be damned”.
Fortunately all my wines I kept there have not suffered from the same phenomenon! I guess it takes much longer for these molecules to traverse through a cork compared to a simple crown or screw cap lined with a thin polymer liner?
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And while the high pressure doesn’t keep oxygen out of the bottle, it still keeps the wine quite saturated with CO2, which - to my understanding - is an effective way of halting oxidation. Even though some oxidation will always occur, its rate is considerably lower as long there is some CO2 in the wine.
This can be seen how the old Champagnes that have retained at least some mousse can appear still relatively youthful and complex despite their evolved nature - it’s not just because the CO2 makes them appear livelier, but because they actually are less evolved. Normally as soon as a Champagne (or any other sparkling wine for that matter) goes flat, they tend to fall apart rapidly. Although I’ve had several tasty old Champagnes that have been completely flat, I’d say every single one of them has been noticeably oxidized. The difference between a Champagne that has a tiny bit of CO2 prickle and a Champagne that doesn’t have any is usually surprisingly great - showing how effective CO2 is at protecting wine from oxidation (although the efficiency drops as the concentration of dissolved CO2 goes down).
You can also notice how many natural wine producers (who bottle their wines without any added SO2) bottle their wines when there is still a little bit of dissolved CO2 remaining from the fermentation. It’s just fizz that’ll blow off when you open the wine (or let the wine age for some years) but it’s one of the non-interventionist winemaking tools that help in protecting the wine from oxidation.
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Also a misunderstanding of CO2. It is not an anti-oxidant, though some winemakers mistakenly believe it is.
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I’ve understood that it is not an antioxidant per se (ie. it doesn’t prevent dissolved oxygen from oxidizing anything), but instead something that is effective at preventing oxygen from dissolving into wine.
For example I’ve heard that during winemaking micro-oxygenation is more or less useless as long as there is a lot of CO2 dissolved in the wine - the oxygen basically just goes through the wine. The winemakers have to get rid of the CO2 or wait until most of it blows off before micro-oxygenation starts to have an effect.
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otto is correct (and I think alan would agree with his 2nd point).
there are very few gases, which upon dissolution in a liquid, actually increase the solubility of other gases in a fixed volume of liquid. most decrease solubility of other gases.
so CO2 doesn’t decrease the likelihood of an individual oxygen molecule oxidizing something, but because there’s less O2 dissolved in the liquid (and also less O2 in the headspace), the oxidation rate drops.
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Phil provided a nice explanation along with a good link. Alan with nice info as well on atomic jitters. If you want to dive into the broader process, Feynman is great.
https://www.feynmanlectures.caltech.edu/I_01.html
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Stunning thread!
I don’t think I’m smart enough to be in here. 
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Alan hit the nail on the head. I would just add that positive pressure does slow diffusion by reducing the available pathways in the pore labyrinth (i.e., the higher the CO2 concentration in the bottle, the higher the CO2 concentration in the cork). So at some [potentially irrelevant] level, the diffusion of oxygen across a cork with a positive pressure of CO2 is slower than it would be if the partial pressure of gases behind the cork were ambient, and your general intuition is correct (but the gases are sufficiently non-interacting that O2 is able to diffuse across the cork). Similarly, contact with liquid, as when a bottle is on its side vs. upright, slows the rate of oxygen ingress by a factor of five (Lopes Cardoso et al., 2022). This is again due to a reduction in the available pathways in the pore labyrinth.
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just be like me. Say nothing and nod slowly, occasionally touching your chin. They’ll think you understand.
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Yeah…got a D in Physics…back to the what are you drinking thread!