There are a number of legitimate reasons for sending a wine back at a restaurant: the wine could be oxidised, be contaminated by ‘cork taint’, suffer from excess volatile acidity, or have unpleasant Brettanomyces aromas. One common cause for complaint, however, is the presence of tartrate crystals or ‘wine diamonds’. Wine diamonds in white wine are a natural occurrence.
These are clear crystalline deposits found usually in certain white wines, especially Riesling. They are either potassium bitartrate (a.k.a. cream of tartar) or calcium tartrate — both found naturally in grapes, and which follow through to the final bottle in the winemaking process. They are certainly not tartaric acid, sugar, or bits of glass! These wine diamonds are perfectly natural and completely harmless. In the glass, they sink to the bottom and will barely impose on your enjoyment of the wine. Or, the wine can simply be decanted, with the crystals remaining in the bottle.
These crystals can be removed before bottling, however it is an involved process involving chilling the wine and passing it through filters. This is energetically expensive and the filtration process can remove flavour compounds that give the wine its complexity and character. Producers of fine wines prefer to mess with the wine as minimally as possible to deliver the best possible quality to the consumer.
So if you do see some wine diamonds in your wine, this is not a cause for complaint. Rather, be assured that the winemaker cares about his wine so much that he has chosen not to remove them to deliver the best possible wine to you!
James Flewellen is The Rambling Epicure wine columnist. James is a biophysicist at the University of Oxford. Originally from New Zealand, the huge range of wine James discovered in Europe spurred his interest in all things vinous. He became involved in the University’s Blind Wine Tasting Society and has recently completed a two-year term as its President. During this time he represented the University in a number of domestic and international wine tasting competitions, winning several awards. He is currently completing the WSET Diploma in Wine and Spirits. James has a passion for wine communication and education and runs the Oxford Wine Blog and wine tasting courses through the Oxford Wine Academy.