What's the cause of pushed corks?

Q: The owner of a small wine shop told me that a customer had come in with a bottle of wine to return. The wine's cork was pushed part way out of the bottle, and wine had leaked out. The shop owner asked that I tackle the subject of pushed corks and proper wine storage.

A: There are two things that can cause a cork to push out of a bottle after the wine has been purchased. One is a secondary fermentation in the bottle, which creates carbon dioxide, which can force the cork out. This is a wine flaw and is extremely rare.

The other is exposing the wine to heat, which cooks the wine, heats up the contents and expands the air inside so that the cork is pushed out, and the wine may leak out the side. This is not a wine flaw. This is a storage problem.

When purchasing wine, it is always a good idea to give each bottle a quick check to make certain that the fill level is correct (it should be into the bottle neck right at or just below the bottom of the capsule; never below the shoulder, except for rare, old wines).

Look to see that the cork is intact, the capsule is not bulging and there are no sticky wine stains on the glass or the capsule. If there are, do not purchase the wine. It has been improperly stored somewhere in transit, or exposed to high temperatures in the warehouse or at the retailer's.

If the bottle is sound when purchased, it is up to the purchaser to keep it stored away from heat, light, vibration and extreme temperature shifts. Putting wine near a stove or a furnace is an obvious no-no, but it could be on a basement shelf under a hot water pipe, and that might potentially be a problem.

It is always a good idea to periodically inspect your wine storage area, no matter how large or small, to make certain that your bottles are lying down and are not showing signs of heat damage. Once the heat has gotten to them, the damage is irreversible.

Paul Gregutt answers questions weekly in the Wine section. He can be reached by e-mail at wine@seattletimes.com.