The crystals come from the tartaric acid present in the wine.
It’s naturally contained in the grape and it’s largely what gives it its freshness and acidity.
Tartaric acid is naturally present in grapes and is a major component of the wine’s freshness and acidity.It’s the drop in temperature that precipitates tartaric acid. Although much of it is precipitated during fermentation and cooling of the wine before bottling, it’s a phenomenon you may see in bottles you let age. This only happens if the bottles are stored horizontally, otherwise the crystals “sink” to the bottom of the bottle.
Tartaric acid also plays an important role in winemaking, helping to chemically stabilize the juice and microbiologically secure the fermentation environment. The acidity of wine therefore gives it better aging potential.
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