Ask how to handle a particular bottle before drinking, and someone is bound to suggest “slow-ox”. In a recent discussion of slow-ox, and breathing/decanting in general (here: The myth of letting wines breath) I argued that slow-ox can’t work because the diffusion of oxygen into a bottle (and, conversely, compounds which might escape the wine beneficially) is much too slow to make a difference to a bottle just sitting open for a few hours.
Just a little digression on diffusion (apologies for the didactism): It can be tricky to differentiate between diffusion (movement of molecules through random motion) and convection (bulk movement caused by other forces). In daily life, we experience bulk movement all the time, but don’t really notice diffusion. A breeze through the window carries the smell of your neighbor’s barbecue through the house; someone walking through the room pushes air around and causes bulk movement; dumping an ingredient into a pot, or milk into your coffee has inertia that stirs things up, or sets up temperature gradients or forces between layers with different densities that move things around quickly; the fan in your oven blows air across the food; Those are all examples of convection. Visualizing diffusion isn’t easy, partly because the things we notice moving aren’t doing so (mainly) because of diffusion; and partly because things that actually are diffusing are doing so at a rate too slow to notice. When you take the lid off the pickle jar and smell pickles, it’s not really because of diffusion, it’s because you sucked some of the pickle aroma up into the air with the lid, and some of that wafts past your nose. You don’t smell the pot of stew on the stove because of diffusion, you smell it because the hot steam is rising and creating bulk movement of air.
Diffusion is a slow process. Glacially slow in liquids, but relatively slow even in gases. For an oxygen molecule in water at 20 degrees C (68 F), the diffusion coefficient is about 2x10-5. Use the online calculator below to calculate how long it would take for O2 to travel, say, 10cm in water. It’s about 29 days. That’s days, not seconds, minutes, or even hours (in air, where the diffusion coefficient is roughly 10,000 times larger, it’s still about 5 minutes).
This is why the alveolar capillary wall, where oxygen is transferred from your lungs to the capillaries that will carry it into your system, is about 0.6 microns thick. Much thicker, and there wouldn’t be time for oxygen and CO2 to diffuse across. It’s why we have a microscopic network of tiny capillaries to carry blood to our tissues - because without that, diffusion alone cannot support life on the scale of a large mammal. It’s why you use an aerator in your fish tank, or plants which produce O2, or agitation of some kind - because diffusion alone can’t bring in enough O2 to keep fish alive in a larger tank.
When you pull the cork on a bottle and just let the bottle sit, there is no bulk movement of liquid in the bottle. Anything that goes in or out must diffuse across the air/liquid interface. Oxygen must cross the barrier, then diffuse throughout the wine to do anything. SO2 or other volatile compounds must diffuse through the length of the bottle to the interface, then escape. And there’s the rub: diffusion is just too slow to make a difference in a bottle of wine. Without agitation, bulk movement, and increasing the surface area greatly, almost nothing is going in our out of that bottle on the scale of minutes, or even hours. You may be able to smell some compounds that have a threshold of human detection down in the parts-per-trillion/billion range (because, like everything else in chemistry it’s all about probabilities, and there are bound to be a few molecules with a lot more energy that can bounce around and escape faster), but you’re not going to get any appreciable amount of O2 in, or other compounds out.
If you still doubt this science, maybe some 1000 word pictures will hammer it home. I scratched my head for a while trying to think of an appropriate demonstration with something you can find around the house, and came up with brown sugar dissolving in water, because it’s easy to visualize. I put about half a teaspoon of brown sugar in a glass of room temperature water, and just left it to dissolve and diffuse. Took a couple of days for the sugar to fully dissolve, and after 4 days, you can see how far it has migrated through the glass (about 3 cm). I was concerned that maybe the color is contained in larger particles that would tend to settle at the bottom, so I did the same with another glass, but stirred it up until everything dissolved. Nothing has settled out, and the color is uniform from top to bottom of that glass.
First day
2 days
4 days
Now, sugar is a larger, more slowly diffusing compound than O2. But the result above is quite consistent with what you get from the online calculator.
The good news is that opening that bottle and leaving it to “slow-ox” won’t hurt anything, so if you remain unconvinced, go on slow-ox’ing, you’re not losing anything by doing it. And if you do, don’t leave it in your cellar, get it on the table at room temp, because diffusion slows down even more as temperature drops.