Now, let’s go back and talk a bit more about those corks and the effect rapid swings in temperature can have on them. Corks work as seals in the bottle neck because of their elasticity. A cork is effectively made up of lots of little bubbles of cork cells. This spongy structure expands and contracts like all solids do when the temperature changes. With age the cell walls progressively lose their elasticity, much like our own skin does, though by different means. Rapid temperature swings can cause corks, particularly older corks, to lose their ability to seal properly in the bottle neck, as can really high temps -- like 140F/60C -- but at those temps we would have other problems to worry about!
If you have a fragile cork that has lost elasticity with age and it is put under stress due to rapid temperature swings, it can fail altogether. Not only does this begin to allow air into your bottle of wine, but if the bottle is laying on its side, it can begin to force wine up past the cork (remember: Fluids expand even more than solids when heated). That little path of wine can dry out but now it’s like a dry creek bed in your bottle. Each time there is a pressure increase in the bottle the wine can work its way up a little farther until finally, on day, it makes a great escape.
The truth is that a bottle can begin to leak after just a fairly brief time of mistreatment; we’re talking hours, here. I don’t buy wines with evidence of seepage, and while some unscrupulous retailers are quite effective at dealing with this sort of evidence, there usually are tell tale signs. The capsules tend to be the final arbiter of whether a bottle was a leaker or not. First there are those two little holes, ok maybe on, on the top of the capsule that allows air to leave the empty capsule as it is forced onto the bottleneck.
If you see wine residue in those holes chances are it came up through the cork. It’s worth checking to see how high the fill level is on that kind of bottle though, especially if it’s a new release. Some producers are notorious for over filling their bottles, causing this sort of stuff to happen when the cork is inserted into the neck. This is particularly prevalent in places that are cold. When that bottle gets shipped to someplace warmer the wine expands and forces its way past the cork, even if the storage temperature is still well within the acceptable limits for wine storage.
The other way that some people use to determine the soundness of a particular bottle is to check and see if the capsule spins freely on the neck. I remain very skeptical about the efficacy of this in determining damage to any bottle. Many capsules are just very tight and others, in the past, frequently used some sort of lubricant to help get the capsule on the bottleneck. With time that lubrication tends to turn into glue, not to mention the fact that old capsules, made of lead, and newer capsules, made of aluminum, corrode in damp cellars, helping to further lock them in place on the bottle’s neck.