Thanks. Really, the one principle that needs to be emphasized is that gases (and liquids, for that matter) don’t “layer” in some stratified way that depends on molecular size. Spraying a little argon into your bottle, for example, won’t result in the argon settling on the surface of the wine and providing a protective barrier. You would have to spray in enough to be sure that all the existing air is pushed out, then seal the bottle. Otherwise, the new argon and remaining air will eventually mix uniformly.
A liquid mixture works the same way, and is easier to visualize: take a glass of coke, for example. The molecules that provide color are much bigger than the water they are dissolved in. But if you leave a glass of coke sitting on the table, the color components don’t settle down to the bottom, they stay mixed evenly. Same with wine. And same with a mixture of gases.
Alan is nailing it. the one qualifier I would put to the below is:
This is true re:size, but elides something. Lack of any stratification in common conditions is almost universally true with gasses. It is true with the liquids you likely encounter in fermentation (alcohol, water etc) , but by no means all liquids. Immiscible liquids can layer essentially indefinitely (see oil and water, or using force to mix liquid-liquid extractions where, after stopping the application of force, phase separation happens again, as a function of density); viscous liquids take a long time to mix if not agitated, and if treated carefully, even miscible liquids take a long time to mix (see layering to diffuse one liquid into another, for crystallization, this diffusion can take hours to days )
If there’s one thing I learned from this thread, it’s: Chemistry is hard.
Seriously though, I often read about winemakers putting a layer or “blanket” of CO2 in their fermenters to protect what’s inside from oxygen. (For example, to promote carbonic maceration.) Are you saying that doesn’t work? Or only works under certain conditions? Or only on short time scales (until the gasses inevitably mix)? Or that some way of sealing the top is required in order for the CO2 to protect the grapes/must from oxygen?
You’re thinking about it exactly right. It works on short timescales, or if you have a constant supply of CO2, or if you seal it up. Dry ice is helpful because it will sit on top of the grapes/must/wine and provide a constant source of CO2 to maintain the blanket and keep air up and away from the grapes. This can be helpful to keep air away from the grapes (and also provide some auxiliary cooling) during a cold soak. It can be helpful to prevent oxygen uptake when you’re filling a tank or tanker truck. If you’re adding dry ice to a tank on a hot September day you might need to top it up daily or more. For carbonic maceration one fairly easy way to do it is to fill a tank with grapes, displace air with carbon dioxide (gas from the bottom valve or put dry ice in before the grapes) and then seal off the top with a check valve so that any gas produced can escape.
Well said, and though many of those scenarios are moving us away from the world of winemaking, it does come up. Plenty of folks have inadequately mixed a tank after an addition. The most obvious example is grape concentrate, which is much more dense than must or especially wine and will readily sink to the bottom of a tank and stay there unless it is very thoroughly mixed in. Tanks can also become thermally stratified when they are cooled, which makes active mixing particularly important when you are doing traditional cold stabilization.
Phil, your join date is after this groundbreaking post of mine (some around here describe it differently ) so you may have missed it lol. Diffusion in liquids takes a lot longer than probably anyone realizes.
I’m convinced that most winemakers don’t realize how long it would take a tank to thoroughly mix after just pumping in wine from a bunch of barrels, without actively stirring quite a bit. I suspect there is a tension in their minds between mixing and thinking they will allow too much air into the tank.
I’m reasonably certain I’ve experienced the result of this, through bottle variation, and from some very well known producers.
Yeah this is pretty common from what I’ve observed. “Rolling” a tank with nitrogen can also help scrub out excess CO2, though it also has the effect of removing some aromatics. Seems to be a relatively temporary impact as the wine comes back into equilibrium, and may be a contributing factor to the bottle shock observed immediately after packaging.
One possibility here is that not all of the ‘same’ wine is bottled at the same time each vintage. Maybe a tank or part of a tank will be bottled one day and another tank bottled several months later. This, of course, isn’t to dispute what you said, only that there may be other possibilities leading to bottle variation across a vintage.
