What? I’ve had lots of wines where the cork has been soaked through for some part of its length; other just a few millimeters, others almost completely through.
Of course these have always been old wines with old corks.
And furthermore, you can’t directly compare oxygen and water molecules (or even more complex molecules of wine) with each other. Of course they work differently from each other. For example, I suspect cork being hydrophobic to some degree, which would allow some O2 permeability without compromising the H2O impermeability.
As mentioned, there are many studies regarding the permeability of cork to gas and liquids, particularly water and ethanol.
APCOR is the Portugueses cork association, and they’ve done plenty of research. There are studies in the Journal of Agriculture and Food Chemistry. There have been studies carried out in Bordeaux and Australia. There are plenty of them around if anyone cares to look.
To summarize:
Cork can be slightly permeable to gas and liquids because cork is not a manufactured product and is used with whatever defects come with it. This is what Ben’s point number 1 is addressing. Remember though that cork cells are hydrophobic, which means liquids are not absorbed, i.e. cork resists liquids.
However, when exposed to air, corks can dry out. This is Ben’s point number 3. But here’s the fun part - in the old days people used to soak corks before putting them into bottles, so they weren’t dried out. Some home wine makers still do that. But you don’t need to if you’re buying commercial corks in quantity. Those are sanitized and have been moistened as much as they’re going to be. They’re often coated as well and kept in sealed bags. And as the Portuguese studies have shown, that little bit of moisture makes the corks essentially impermeable to oxygen and other gasses. Finally, when a cork is put into a bottle, it is compressed. Corks are slightly larger than the bottleneck, which is why it’s hard to put them back into your bottles once you open a bottle. That compression makes it even more resistant to gas and liquids. So you’ve decreased the permeability of the cork by adding whatever moisture it can absorb and by compressing it, and then if you’re a wine molecule, you’re going to need to get through two or more inches of that material.
When you look at the studies, look at what they were measuring and how they did it. You can take a piece of cork and test permeability. You can stick a cork into a tube to mimic a bottleneck and measure permeability. Or you can actually stick it into a bottle of wine and measure permeability. You’ll get different answers depending on what you do. The studies where they used actual full bottles indicate that with good corks, there can be measurable oxygen diffusion for the first few months and even up to a year, after which there is no more. Storing a bottle on the side showed no effect on the diffusion of oxygen, which comes from the cork and the headspace.
I’ll add the come in air sealed bags. Once opened, manufacturers recommend using them within a few months. They’ll also take them back and recondition them for you. That can make sense if you don’t use too many of the last 1000 cork bag. Pay some bucks and get back a sealed 870 cork bag.
The studies where they used actual full bottles indicate that with good corks, there can be measurable oxygen diffusion for the first few months and even up to a year, after which there is no more. Storing a bottle on the side showed no effect on the diffusion of oxygen, which comes from the cork and the headspace.
Interesting, and makes sense. I’d again stress that the weak point is between those corks and the neck, as the corks expand and gradually resolve their micro-seam issues.
A friend did a dissertation on an alternative cork made with sugar can fibers. On paper, they are much less permeable than corks, less expensive, sustainable and more. He was completely sold and used them on a noncommercial wine (whew!). They leak. A pretty high percentage stored neck down or one their side. That includes ones that spent the first few months neck up, then put on their side. (Standard cork manufacturers recommend keeping the bottles neck up for 12-ish hours to avoid leakage while the corks expand, then flipping them over. No one does that.)
Greg makes lots of good points here. I will say that there is a lot of data on the science of wine and it is of variable quality. I don’t say that to pooh-pooh the specific study cited, just to avoid putting too much stock in any one study - something to be particularly careful about if you’re looking at a study on cork integrity funded by a cork association.
To add my $0.02 re: Nate’s point about many corks not showing any significant diffusion of red wine into them, it’s true that corks that perfectly retain their integrity are not significantly permeable on timescales relevant to the aging of wine (as Greg describes above). That’s a big qualifier though. All of us have looked at a lot of corks over the years: it is pretty common to find corks with some linear pore structures in them if you cut them enough ways. All you need is one path, be it at the cork-bottle interface (due to cork desiccation, which is mitigated by storing the bottle sideways) or inside the cork itself, and you can speed up that diffusion to a point where you have issues. In badly compromised corks you might see several channels. And corks are organic products and do slowly break down over time, though on the 10-50 year timeframe you’d expect that not to be too much of an issue.
(As a sidenote, corks with major channels into the wine are probably more likely to present TCA problems, since there is a larger surface area of cork interacting with the wine, giving you a higher probability that nasties inside the corks interact with the wine in the bottle. I’ve observed this in “TCA-free” treated natural corks. Perhaps an argument against storing wine on its side?).
I would agree with Ben Mandler. There is a difference between a fully wetted cork and one experiencing 100% humidity. In the fully wet cork (with the bottle on its side, or upside down), the bottom of the cork only sees liquid, so the diffusivity is that of the liquid films within the very small, mostly or entire unconnected pore network. When the liquid is not in contact, some percentage of the pores may be not fully liquid filled, so gas permeability or diffusivity comes into play. The diffusivity of gases is about 4 orders of magnitude larger than that of the same constituents (e.g., O2) in the liquid phase. In a soil, below the water table the ingress of O2 drops to much lower values (even given the much much higher permeability of natural soils compared to cork). Above that point, even with 100% humidity (which is normally the case), the transport rates increase. This is why we often see oxidation extended right up to the water table, where the liquid is 100% (and not the humidity).
In any case, humidity represents water vapor (gas), so not the same as liquid water…
But the effect on cork swelling and closure of connected pathways may be more important in this regard. Admittedly it is difficult to take observations from relatively porous and permeable formations like soils and apply them to a complicated porous medium like cork, but we are also normally talking about much longer time scales.
It seems to me that cork do breathe, albeit very slowly. To take Alan Rath’s point above and turn it around, the fact that ullage is observed typically after enough time means there is a loss of water vapor from the system. The test would be to see if a bottle stored upright shows no ullage after 20 years or so.
Interesting paper by Oliveira et al (2015) Cork Structural Discontinuities Studied with X-Ray Microtomography. Attributes the early O2 ingress into the wine through cork due to compression of the cork when bottling occurs, with oxygen filling the structural defects in the cork.
From the paper:
Rib é reau-Gayon
(1933) suggested that the initial high oxygen ingress is due to the high internal pressure in the cork cells created when the cork Sts are compressed into the bottleneck (see also Lopes et al. 2007 ). Therefore the initial high ingress rate of oxygen into the bottle should be related to the cork structural discontinuities, i.e., more specifically to the void fraction and the air located there. Apart of the first period, gas transport through the cork cells occurs with very low diffusion rates through small channels (i.e., through the plasmodesmata) present in the cork cells walls ( Faria et al. 2011 ).
Logically, I would think that corks will dry out in a dry environment and won’t in a humid environment, regardless of bottle orientation. A bunch of anecdotal experience that I have (storing many bottles upright and many on their sides, some in a quite dry basement and some in a quite humid basement) seems to support that. I don’t know why people believe “common knowledge” without thinking about whether or not it’s supported by facts or even makes sense.
To add my $0.02 re: Nate’s point about many corks not showing any significant diffusion of red wine into them, it’s true that corks that perfectly retain their integrity are not significantly permeable on timescales relevant to the aging of wine (as Greg describes above). > That’s a big qualifier though. > All of us have looked at a lot of corks over the years: it is pretty common to find corks with some linear pore structures in them if you cut them enough ways. All you need is one path, be it at the cork-bottle interface (due to cork desiccation, which is mitigated by storing the bottle sideways) or inside the cork itself, and you can speed up that diffusion to a point where you have issues. In badly compromised corks you might see several channels. And corks are organic products and do slowly break down over time, though on the 10-50 year timeframe you’d expect that not to be too much of an issue.
I think that summarizes things perfectly. Unfortunately, it is a big qualifier. Maybe a different way of looking at it isn’t to say that cork is the problem, but rather that corks are the problem.
This is an interesting topic, and is interesting to read other’s thoughts on this. I personally have no knowledge other than what I see in my cellar. I usually go up to 60 F in the summer, and maybe 48 F or so in a normal, cold winter. I usually have the humidity cranked up in my cellar all year long- I am sitting at 81% right now. Whenever I open wines that have been in my cellar since the beginning- about 18 years now- my corks are in excellent shape with virtually no creepage on the corks in most cases. I have to say that I almost never see 20+ year old bottles from anywhere that don’t show some creepage on the corks. And my wines seem to taste young compared to other notes I read. Regardless of what science may say about corks- I will continue to store my bottles on the side in a high humidity environment.
These linear features are basically what the article I cited was talking about. They show up clearly with X-ray microtomography. A reason why natural corks may underform engineered corks, which are free of these linear features.
Anyway, all of this discussion about corks misses the point about how 100% humidity is different than a cork bathed in liquid. Basic physics…
