I used to work in a wine shop. One day an unhappy customer came in with a bottle of wine she had bought a few weeks previously. It had, she said, a worm in it. I looked and there was indeed a worm-like shape in the bottle. However, I also knew that it was far more likely to be sediment that had formed into a chain. The wine was 10 years old and made by a small artisan producer. Sediment can form in both red and white wine. Neither is harmful, and for some consumers it is a positive – evidence that the producer hasn’t interfered with the wine too much.
In the case of white wines, small sugar-like crystals can form either on the cork or fall to the bottom of the bottle. Sometimes called wine diamonds, (which sounds less threatening), these are potassium bitartrate crystals, formed during the winemaking process. They are caused by tartaric acid, the primary acid found in wine. They taste of very little, sometimes having a lightly acidic tang.
Tartaric crystals form at low temperatures, and so are often found in white wines that have been refrigerated or kept in cold cellars for a period. Many producers now cold-stabilise their wine before bottling, so you are unlikely to come across it. Very occasionally white wines can have a haze, known as protein haze. While harmless, it is unsightly and is considered a fault. Bring the bottle back.
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In red wine, sediment is formed by polymers. These are molecular chains made up of tannins, anthocyanins and other phenolic compounds. As a wine ages, the colour lightens as the anthocyanins drop out, and becomes smoother as the tannins polymerise. These form chains – hence the “worm” in my customer’s wine bottle. There may also be dead cells leftover from fermentation. As with white wines, sediment found in red wine is harmless but not very pleasant. This is why wine drinkers decant old bottles of vintage Port and Bordeaux, both tannic wines that are likely to throw a sediment. If you think your wine might have sediment, stand it upright for 24 hours, and pour carefully, stopping when you see some sediment appearing.
As for the unhappy customer, in consultation with the producer in Bordeaux, we sent the bottle for chemical analysis, who confirmed it was sediment, so we replaced it with a couple of (younger) bottles of the wine. I have come across genuine wildlife in wine bottles on two occasions, one a fly and the other a wasp. Obviously, the producer did not take great care of their bottling line.
