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Understanding Tartrates Crystals in Wine and the Effects of Cold Stabilization

We have all experienced the joy of opening a phenomenal bottle of wine just to be surprised by small crystals on the cork or particles suspended in the wine. Don’t panic – those small crystals are called tartrates and they are simply a sign of how the wine was made and are harmless to you and your wine. Tartrates – or more lovingly, “wine diamonds” – are formed from tartaric acid which is naturally occurring in all wines and provides structure, balance and flavor.

The truth about wine’s acidity

Tartaric acid is one of three main acids found in wine grapes alongside malic, and citric acids. Each type of acid plays a key role in the wine production process and contribute different flavor profiles and textures to the end wine. While malic acid does contribute to the aromas of a wine, it is more known for its role during the winemaking process through malolactic fermentation. In this process, the stronger malic acid is converted into the softer, smoother lactic acid. On the other hand, tartaric acid is arguably the most important in wine due to the prominent role it plays in maintaining the chemical stability of the wine, the wine’s color and influencing the taste of the finished product.

During the fermentation and barrel aging process, less than half of the tartaric acid present in a wine will settle out and bind with lees, pulp debris and precipitated tannins and pigments. Majority of the tartaric acid will remain soluble throughout the production process. The remaining tartaric acid present in a wine is the primary acid one tastes and is essential to the final mouthfeel and balance, adding an additional layer of complexity to a wine.

What are tartrates and why do they form?

Tartaric acid’s solubility in wine is temperature-dependent. When a wine is chilled to temperatures below 40 degrees, the remaining tartaric acid will bind with the naturally occurring potassium in the wine to form crystalline deposits (potassium bitartrates), or tartrates.

This phenomenon is rarely an issue for red wines as sediment is expected to accumulate over time. However, for white wines which are often refrigerated before serving, these tartrate crystals may be alarming. Tartrate crystals in white wine have been described as having a similar appearance to shards of glass or have been mistaken for unwanted or unnatural sediment – this is simply not the case. Though their appearance may be a bit off-putting, tartrates are completely harmless.

Cold Stabilization: negative effects on wine

Some winemakers choose to cold stabilize their wines to eliminate the future formation of tartrate crystals. Cold stabilization is the process of cooling the wine to around freezing temperatures in large stainless steel tanks for several days or weeks after the wine has aged and just before bottling. By cooling the wine prior to bottling, the potassium bitartrates will crystalize and drop to the bottom of the tank where they can then be filtered out of the wine. By doing this, the winemaker is ensuring that further tartrate crystals do not form in the bottle mainly for aesthetics reasons. However, at the same time, cold stabilization strips the wine of it acidity, takes away from its natural flavor profile and impacts the wine’s long-term ageability.

At Stonestreet Estate Vineyards, we are passionate about producing the best possible wines from our mountain estate and choose not to cold stabilize in order to maintain the natural acidity, flavors and texture of our wines and protect the wine’s quality and aromatics. Stonestreet wines are meticulously produced to ensure that each wine reflects the uniqueness of its terroir while remaining perfectly balanced – ready for your wine glass. Many in the industry - Winemakers, Sommeliers and Academics -view “wine diamonds” as a sign of quality, indicating that the wine was not over processed or manipulated.

How to avoid tartrate crystals

Proper wine storage will help reduce the formation of tartrates. Quality white wines should be stored on their side at 55 to 60 degrees and only chilled to 45 to 48 degrees (depending on the varietal) just prior to serving to avoid the development of tartrate crystals.  If wine diamonds do appear, don’t panic! Simply pour the wine through a filter or cheese cloth into a decanter prior to serving. You may also choose to decant the wine normally by letting the crystals settle to the bottom then pouring the wine slowly into your decanter at a slight angle.

For more information on tartaric acid and wine diamonds, contact our team at 707-857-1524 or wineclub@stonestreetwines.com.

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