Sugar crystals on wine cork naturally made and un-stabilized wines develop crystals, which generally precipitate to the bottom of the bottle or attach themselves on the cork or the closure of the bottle. Sometimes referred to as “Wine Diamonds” they are indicative of good quality. Although crystals are bitter, they are harmless and do not affect the flavour of the wine in any way.
When grapes are de-stemmed and the free-run juice is obtained, the must naturally starts to ferment. The yeasts are on the skin of the grapes. When yeasts discover sugar in the must and oxygen, they start converting the sugar into alcohol and carbon dioxide. The must contains potassium from the soil, and tartaric acid, a natural component in ripe grapes.
During the fermentation the alcohol content increases gradually and potassium is combined with the bitartrate of the tartaric acid, thus forming potassium bitartrate in liquid form. (The powdered form of this is known as cream of tartar and used in baking.)
Alcohol induces the salt of tartaric acid to harden and most of the tartaric acid in insoluble form precipitates to the bottom of the fermentation tank or container, either shortly before, or after the fermentation stops.
When the newly made wine is cooled, more tartaric acid in insoluble form precipitates to the bottom of the tank. During bottling the wine is channelled through stabilizers. They consist of cooling pipes capable of dropping the temperature to – 4 C, which turns insoluble tartaric acid to crystals. Crystals are filtered thus making the wine brilliant. Occasionally some of the wines exposed to temperatures which are lower than the temperature by which the tartaric acids were removed, may attach themselves to the cork and precipitate to the bottom of the bottle.
Tartaric acid can be totally removed, but this process deprives the wine of some congeners (taste imparting particles).
Consider yourself fortunate if you obtain a wine which contains wine crystals or diamonds.
Simply remove the tartaric acid by either decanting the wine or separating the sediment from the wine. If it was clear at the time of bottling it will be crystal clear.
If wines enclosed with natural or synthetic cork are correctly stored, i.e. laying on their side, the tartaric acid particles will adhere to the cork. In the case of screw capped bottles tartaric acid will precipitate to the bottom of the bottle. Simply wipe the inside of the bottleneck and pour the wine.
Although both red and white wines contain insoluble tartaric acid, one more frequently finds crystals in sweet white wines, as they are stabilized at lower temperatures than dry whites.
Wine crystals or wine diamonds are indicative of quality and never impart an unpleasant taste.
To your good health!