Why would a bottle sealed with a synthetic cork ever leak?

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Dear Dr. Vinny,

I bottled a batch of wine with synthetic corks and knew that I didn’t have to rush to lay them on their sides, so after a month of standing, I laid them down. Two days later, I opened a bottle and a little wine had leaked out. Why?

—Linda, Canada

Dear Linda,

Home winemaking isn’t really my forte, so I typically avoid questions referring to it. However, I recently received a few different questions about synthetic corks leaking, and I think I can help shed some light on this issue.

Corks can leak whether they’re traditional or synthetic. I mean, think about it—you’re taking a plug of compressed material, squeezing it down into the tight cylinder of the neck of a wine bottle, and then hoping the cork will expand uniformly and snugly. Things can go wrong.

I’ve heard that when bottling with natural corks, it’s recommended, as you suggest, that the wine bottles stand upright for a few days before laying them on their sides, which will give the former tree bark a chance to expand completely. After that period, storing bottles sealed with natural cork on their sides is recommended, because keeping the wine in contact with one end of the cork will help keep the cork from drying out. If the cork dries out, not only will it turn to sawdust when you try to open the bottle, it can also compromise the wine inside. (Natural cork can also be the cause of so-called “corky” bottles of wine, which are contaminated with the harmless but unpleasant chemical compound TCA.)

Synthetic corks are supposed to expand and seal instantly, but some of the synthetic corks can be firm and not as squishy as natural cork, so they don’t rebound as well after being compressed. I’ve certainly come across some leaky ones in my experience, as well as ones that were so tight that they seemed near impossible to extract. For home winemaking, it seems that sometimes home corking machines can crease, score or create a burr on a synthetic cork, and wine can leak out along these marks. Make sure to check the machinery you’re using.

Keep in mind there are still other alternatives to seal bottles of wine, including twist-off closures and crown caps, like you see on beer bottles.

—Dr. Vinny

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