This is really the key, just how miniscule is miniscule? Because we are talking about rates over 20-30+ years for some wines and even small rates could add up. Does anyone have any data on diffusion rates through a sound cork as a function of cellar humidity?
Okay…but forget ullage – what about cork shrinkage? Is that not a legit concern for wines stored over a long period of time?
Diffusion rates thru a membrane are proportional to the concentration gradient. The water concentration at the wet end of a cork is literally hundreds of thousands times greater than at the dry end, nomatter the humidity of the cellar. So if you believe that water can diffuse thru cork, then any water lost from the dry end should easily be replaced by water entering the cork from the wet end.
I don’t know of any such studies and, IIRC, the problem in determining diffusion rates thru cork is that water and oxygen molecules tend to find it much easier to pass thru the seal between cork and glass than thru the cork itself. In fact some believe that all the transmission is thru the cork/glass seal, and that variations in the quality of this seal account for much of the bottle variation we see as wine ages.
I have my wine in the basement against a subterranean wall. Exposed to the indoor elements, but stays pretty cool here in Virginia, even in summer.
I run a _de_humidifier in the basement during wet periods, sometimes days on end. I keep it in a separate room from the wine, but if you believe the manufacturer the dehumidifier will suck all of the excess moisture out of a 1000 sq ft+ space.
No real point to this, except to say that I’ve decided that guarding against potential mold/mildew in the house is more important than babying the wine. I hope I don’t regret the decision a decade from now, but I’m not losing sleep over it. Do others deal with this (mild, frivolous) dilemma?
Awesome fact based analysis. But you overlook one thing, that daily pressure change acts as a diurnal engine for gas exchange.
Daily fluctuations accelerate oxidation by causing the cork, a porous membrane, to breathe in an out. Diurnal temperature shifts cause the cork to “breathe faster.” You accelerate the movement of gas (air) diffusing/exchanging in the cork.
Joe - you can’t correlate barrels and cork. Barrels are made from the wood of the tree. Cork is bark. One of the purposes of bark is to prevent water from being lost as it’s traveling up and down the tree. While cork may be 6-8% water, it is like 80-90% air. It’s made of hexagon cells that are basically like little balloons filled with air. The problem is that those hexagons don’t fit together perfectly - there are imperfections here and there and those are partly what makes it impossible to say anything about a particular cork and why there is so much variation between corks. They’re not manufactured products, so you can never be consistent.
As far as those folks saying that the speed of a temp fluctuation matters - what exactly is it that makes speed relevant? If your wine gets really hot in an hour and stays that way for two weeks, or if it gradually gets really hot and stays that way for two weeks, what is the difference? Whatever it is that you don’t want to happen when the wine gets hot is going to happen. It’s like the story of the frog that you drop into a pan of boiling water or into a pan of cold water that you heat up. The frog cooks either way.
Peter, sorry, I can’t really go for that kind of hand-waving. And I don’t think it’s true either. Oxygen transport (diffusion) through a good cork is so miniscule that whatever changes there might be by virtue of temperature going up and down has got to be almost infinitesimal. The only thing that changing temperature does to a bottle of wine (IMO) is a) change the total volume of liquid inside the bottle, and b) alter the reactions rates.
Alan’s comments also support the idea that the humidity is largely irrelevant as well, except for the possibility that low humidity may increase the chance of cork shrinkage.
That does not push the cork out, but does create minute inward and outward gas flow through the cork. When you change internal pressure, increasing then decreasing, it minutely increases the movement of gas in the cork.
Throw in the fact that the solubility of gas in liquid decreases as temperature increases, and the solubility of gas in liquid increases as temperature decreases.
The mechanism is there for temperature fluctuations in a bottle of wine creating an engine that accelerates gas exchange through the cork.
You cite 1.3 pounds of force. That may not be enough to push a cork, but its enough on a daily basis, especially at higher ranges, to create a mechanism for increasing the rate of gas exchange through the cork. ![[snort.gif]](/uploads/db3686/original/2X/b/bdc3944606213c4dca6c1169cf0a166c8bc4f8c9.gif "snort.gif"){kind=small}
I bought a TTW cooling unit many years ago so I wouldn’t have to read these threads–but I still do. Just a bad habit, I guess.
Alan’s terrific table can be written another way.
The first column is wine temperature.
The second column is the volume of wine assuming it starts out at 750ml and 55°F.
The third column is the head space above the wine assuming it starts out at 6ml (2cm below a 2cm dia cork).
The fourth column is the pressure generated in the head space assuming no gas or liquid escapes thru the cork.
50°F, 749.8ml, 6.2ml, -0.5psig
55°F, 750.0ml, 6.0ml, 0.0psig
60°F, 750.3ml, 5.7ml, 0.8psig
65°F, 750.7ml. 5.3ml, 1.8psig
70°F, 751.1ml, 4.9ml, 3.2psig
75°F, 751.6ml, 4.4ml. 5.2psig
80°F, 752.1ml, 3.9ml, 8.0psig
90°F, 753.4ml, 2.6ml, 18.6psig
100°F, 754.8ml, 1.2ml, 58.8psig
You can see why corks leak or get pushed out when bottles are left in a hot car!!!
Alan used 3ml head space, I think that applies to bottles with a high fill and you can see that these would leak at any temp over 80°F, and if no leak and only 0.9ml headspace remaining, the pressure in the bottle would be 35psig!!!
My thought is that if bottle temp increases slowly gas/liquid has time to find its way out thu the glass/cork seal and you see leakage. However if bottle temp increases quickly there is no time for leakage and the cork gets pushed.
+1
Comparing the impact of humidity on wine in barrel with a finished, corked wine is really apples and oranges.
I get the point, but the original post was asking about seasonal variations. I highly doubt that a gradual temperature rise in the spring, and drop in the fall, can amount to a significant exchange of air. I assume that bottles with corks start with positive pressure from the insertion of the cork, and in addition have excess CO2 in solution. For years there must be slight egress of air as the pressure equalizes.
In any case, absent studies comparing oxygen intake in bottles kept at a steady temperature, compared to 4-50 fluctuations from 45 to 65 degrees, we really don’t know.
All I do know is that my old wines show as well after passive storage in those conditions as wines from controlled storage they are matched with in blind tastings. Anecdotal evidence only, but enough to give me confidence.
Peter Hickner
Just another thought, but when a bottle is lying on its side the air space is trapped within the bottle and only wine is in contact with the cork. So if the pressure increases there will be no air exchange with the outside, and if the pressure increases enough then wine will be forced out, not air.
On the other hand if you put a room temp wine into your cold cellar, the wine volume will contract, create a vacuum and maybe suck air in thru the cork.
my thought about sudden shifts vs gradual, was analogous to taking a frozen glass and dipping it in boiling water, versus a 24 hour gradient. the sudden shock to a crystalline (or fluid) system would seem to be more likely to introduce failure.
i am merely a stupid lawyer, not a scientist or wine pro. this is merely based off intuition.
Me too but your reasoning is off - the reason glass cracks is not because of shock to a crystalline system.
Glass is actually an amorphous solid and in some respects, closer to a liquid. It’s strong but like most things, expands and contracts with temp fluctuations. At the temps we’ve been talking about for wine cellars, there isn’t much change. But remember that there’s some thickness to glass, even to Riedel, and although it looks perfectly smooth and shiny to us, there are always microscopic tiny ridges and cracks.
When a glass it really cold or really hot, and you’re talking about temp differences of 180F or more, and you put it into the opposite environment, the surface glass wants to expand or shrink, albeit still to a very small degree. However, it’s prevented from doing that by the glass at the core. That creates a lot of tension and even a small imperfection on the surface can be the weak point at which it starts to crack. It’s why you shouldn’t put hot glass dishes on a cold granite or marble surface. But the whole event has nothing to do with wine because wine, unless it’s frozen, doesn’t have surface and inner temp differentials.
That does not push the cork out, but does create minute inward and outward gas flow through the cork. When you change internal pressure, increasing then decreasing, it minutely increases the movement of gas in the cork.
Peter - your two sentences don’t necessarily refer to the same thing. I think the second one is correct. The air is in cork, not through the cork. There’s a belief that air has to go through a cork for a wine to age but a perfect cork is a perfect seal. However, as mentioned, cork is mostly air. At the temps discussed, we can assume no real change in the volume of the liquid or solid, i.e. wine or bottle. But if there’s a slight increase in the volume of the air, why would we think that it blows out through the cork, or comes back in through the cork? If it can’t come out, it has to be dissolved into the wine. This has very little to do with whether a temp change is gradual or not.
As each of the tiny little cell “balloons” in the cork expand and contract over time, they get tired. In addition, the surface cork cells that are in contact with the hard bottle end up losing their elasticity over time. It’s a friction fit so you want really high friction, which the elasticity gives you.
I can’t help but love how this thread has really proven nothing.
![[berserker.gif]](/uploads/db3686/original/2X/8/8600bbd4810d342b8fbd4ffb62b4f0026275fd37.gif "berserker"){kind=small}
In my business we have tests that speed up normal wear and tear. Maybe there have been stress tests done on cork sealed bottles that replicate the effect of temperature changes.
Anyone know of any?
I like Greg’s observation that pressure changes inside the bottle will compress and relax the cork rather than push air in and out. This also is something that can be tested rather than guessing.
P Hickner
Alan, you ignored the effect of the change in temperature on the volume of the gas in the headspace. Back of the envelope, that roughly doubles your numbers. And I think that’s enough to cause problems, especially if we’re talking about the gas finding a weak spot to pop a leak, rather than pushing the whole cork out.
Alan, you ignored the effect of the change in temperature on the volume of the gas in the headspace. Back of the envelope, that roughly doubles your numbers. And I think that’s enough to cause problems, especially if we’re talking about the gas finding a weak spot to pop a leak, rather than pushing the whole cork out.
The gas volume in the headspace shrinks when the temperature rises, because the liquid compresses it. Maybe you meant the rise in pressure? That’s roughly a 10% effect with temperature rise from 50F to 100F, (delta-T)/T with T measured from absolute zero. The pressure rise is dominated by the liquid expansion, basically because there is so much more of it, and because it is much less compressible.
-Al