I left a bottle of wine in a hot car, and found that the cork had pushed itself partly out of the bottle. Why?

The question

I left a bottle of red wine, just purchased, in the trunk of my car yesterday – the temperature was quite warm. Today I took the wine out, and the sealed cork was pushing out of the bottle. I thought I might have mistakenly purchased a bottle of opened wine, but I would have noticed that. Can the heat have caused this?

The answer

Yes! No need to come up with alternative theories. On a warm or even merely sunny day, a car’s trunk can become a sauna, particularly if the vehicle is painted a dark colour that absorbs light. I recently left four bags of sheep manure in the back of my Subaru for 24 hours and the heat must have spurred microbial activity, because there was lots of condensation and pooling of liquid in the trunk – you don’t want to know about the gooey mess.

When a bottle is exposed to such heat, the liquid inside wants to expand beyond the confines of the rigid glass. Hydraulic pressure consequently forces the cork out of the neck, taking the tin or plastic capsule with it. In some cases the cork may not move but the liquid will nonetheless seep out through the interface between the cork and bottleneck, creating a sticky residue on the outside of the bottle.

It’s very likely that the wine will have suffered in the process, taking on a bruised or cooked quality – more prune than plum, for example, or more raisin than fresh berry. Occasionally, I’ve found such wines to taste just fine. However, you should drink yours fairly soon, within a couple of days. Excess exposure to air for an extended period will oxidize the wine and rob it of freshness.

But look on the bright side. At least you didn’t forget four bags of manure in your trunk.

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