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A friend recommended microwaving corks in a bowl of water to sanitize them…


Simon Cole • United Kingdom asks,

A friend recommended microwaving corks in a bowl of water to sanitize them. Is this a better alternative to soaking them in sulfite solution?


alt Corks seem to be on everyone’s mind as of late — it must be bottling time! As I think I’ve mentioned before in this column, it’s impossible to sterilize corks and it’s almost impossible to properly sanitize them. Corks are plugs of tree bark, after all. Mold and bacteria are held in check relatively well by cork manufacturers who use ozone, high pressure, sulfur dioxide and all manner of things to knock down the populations of microbial visitors.

As I mention above, however, once the bag from the manufacturer is opened (as they are in most home winemaking supply stores) all bets are off as the protective sulfur dioxide dissipates, the corks dry out and mold and bacteria take their toll. This is why many home winemakers choose to attempt to sanitize corks before using them — we clean and sanitize the rest of our winemaking equipment, so we at least make an attempt at sanitizing our corks, right? Also, that little bit of moisture can sometimes help the corks slide better into the bottles since we don’t have the benefit of the pounds of pressure of commercial corking machines.

But is microwaving corks the best way to do it? Since it’s impossible to sterilize corks with high heat (that would take a hospital-grade autoclave which a microwave would never accomplish) it’s quite possible that you might only be able to heat the corks to a warm internal temperature that might encourage, rather than discourage microbial growth. My advice is the same as my previous answer. Try to get unopened, fresh bags of corks and use them up among a group of friends or your winemaking club within a month or two.

Response by Alison Crowe.