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Tartrate crystals
Physical and stabilityRecoverable if caught early
Nothing. Clear crystals in the bottom of the bottle or stuck to the cork, often mistaken for glass.
What causes it
Potassium bitartrate falling out of solution when the wine gets cold. Not a fault at all, and harmless.
Detection threshold
Visible.
What you can do
None needed. Decant off them if the appearance bothers you.
How to prevent it
Cold stabilise: hold the wine near freezing for a fortnight before bottling and they drop out in the carboy instead of the bottle.