You see those specs on the end of the cork? Those are called Tartrate Crystals, which are also known as "wine diamonds". They are a natural product of the wine, and form when the wine gets too cold. It is in essence cream of tartar, forming because of the temperature change. Think of sugar turning into rock candy and you'll have a good mental image.
Tartaric acid is a normal grape acid. Potassium also exists in grapes, and when these two things bind together under chilly conditions, they form little potassium bitartrate crystals, which then settle to the bottom of the bottle. They're completely harmless, and quite natural. The problem, of course, is with appearances.
While in Europe these crystals are accepted as a sign that the wine is a natural one, and even appreciated, Americans are used to wine being clear, pure, filtered, processed and de-sedimented. Consumers often panic when they see little crystals in their Cabernet, thinking they are impurities or even bits of broken glass. They often refuse to drink the wine and return it to the winemaker, who promptly serves it to his own family.
De Beers...eat your heart out. I'll take my wine diamonds any day ;-)

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