Sugar Crystals or..?
There's sugar on my cork.' Is a frequent one... no, not sugar but crystals of tartar sometimes called 'wine diamonds' which look - but do not taste - like sugar. They upset people - unless those people know in advance that they can occur and are a GOOD sign. Tartaric acid occurs naturally in all wines. It can be removed but the process also removes a lot of wine flavour so the most conscientious winemakers avoid using it. Crystals of tartar sometimes precipitate out and settle on the glass or the cork or at the bottom. Pour carefully and rejoice in good natural wine.