The purpose behind cold stabilization is to remove tartrate crystals from a wine during its fermentation stage. At Vintner’s Cellar we cold stabilize by chilling your wine in our walk-in freezer for a week, then we filter and degas your wine prior to bottling.
Commercial wineries cold stabilize their wines to avoid tartrate dropouts also known as wine diamonds. Cold stabilizing is the process of dropping the temperature of the wine, after fermentation, to close to freezing. This causes the crystals to separate from the wine and stick to the sides of the holding vessel. When the wine is drained from the vessels, the tartrates are left behind. In general, it is more common for white wines than red wines to be cold stabilized because consumers commonly store white wines at colder temperatures, which increases the risk for bottle precipitation.
Winemakers often cold stabilize wines to obtain a flawless, clear product. If a wine is refrigerated or kept in a cold cellar, the crystals may precipitate out of the wine and settle at the bottom of the bottle or glass. Wine drinkers often confuse these harmless crystals with glass fragments. The crystals may also appear smaller and darker in color, but they are harmless and pose no health risk.
Some of our customers have asked us about crystals they find from time to time in their wine. These crystals are known as Wine Diamonds or tartaric acid fall out.
Wine diamonds are crystals sometimes found in the bottom of wine bottles. Wine diamonds, or potassium acid tartrate, is a mono-potassium salt. In its natural state, it is commonly found in many fruits but predominately in grapes. You may notice these crystals when you remove a wine bottle from your refrigerator or cold storage since it’s cold temperatures that cause diamonds to form. It is entirely natural and is NOT a defect. In fact, it reflects the high quality of the wine.
There is a correlation between wine diamonds and the quality of a wine: the longer the grapes hang on the vine, the more wine acid will accumulate in the grape, this wine acid is the building block of wine diamonds. In other words, wine diamonds are an indicator that the grapes ripened for a long time, an important precursor to crafting high quality wines.
Wine diamonds are also a sign of natural fermentation. By natural fermentation we mean the yeast works with the natural sugars present in the fruit and not by adding inverted sugars.
Tartaric acid, the primary acid in all grapes, is one of the components that promotes a crisp flavour and graceful aging in wine. When tartaric acid combines with natural occurring potassium they form potassium bitartrates or cream of tartar. Wine diamonds can be found in both red and white wine, they absorb the red or brown pigments from red wine and in white wine they can look like shards of glass. Wine diamonds are harmless, have no effect on the flavour and only impact the wine visually.
Tartrates can be routinely found in commercially produced wine and considered a sign of quality. The process of tartrate crystal formation is very hard to predict and tends to occur in 100 % pure grape juice varietals that do not require the addition of inverted sugar.