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Tartaric stabilization of wine.

Tartrate crystals, also known as wine diamonds, from a bottle of wine.

Tartaric stabilization is a process used in beverage manufacturing. What does it do? And how does it do it?

Winemakers use the process to help prevent the formation of tartrate crystals or “wine diamonds” in wine bottles.

Although the crystals are tasteless, many consumers don’t like debris in their drinks. Some wine experts contend their presence indicates a high-quality, natural wine. Others say these diamonds remove some acid from the juice.

Tartaric acid typically is synthesized by plants. It is found in the skim and outer flesh of grapes. It can be extracted when berries are crushed and pressed, according to Valorization of Wine Making By-Products, edited by Matteo Bordiga. Higher amounts of tartrates are expected from grapes grown in cooler climates, which naturally have a higher acid level.

The fermentation process makes potassium bitartrate precipitate, forming crystals. Calcium tartrate usually occurs in wine when and if calcium carbonate is used for deacidification.

Austrian winemaker Höpler GmbH explains:

Tartrate Crystals are a natural product of the wine. They form when the wine gets too cold. Think of sugar turning into rock candy and you’ll have a good mental image.

Stabilization Before Bottling

Rather than rely on a consumer to decant or filter a fine vintage wine, some vintners opt to stabilize wines before bottling. Traditional cold stabilization is a complex process, involving cooling the wine to force crystal formation. This is followed by an involved series of steps concluding with filtration. Some wine experts contend that cold stabilization treatments affect the taste and aroma of the wine.

European researchers explain:

Tartaric stabilization is an important phase of winemaking process, performed on about 70 percent of European wine. […] Presently, winemakers can follow two different strategies: the subtractive way, that eliminates from wine the excess of compounds leading to crystal formation (elimination of tartrate or potassium or both through cold treatment, resins or electrodialysis), or the additive strategy, consisting in adding to wine substances that inhibit the formation of crystals while preserving the original wine composition.

There are issues associated with using some additives, many of which tend to be less expensive and less reliable in inhibiting crystal growth.

Membrane-Based Technology

Membrane-based technologies are being increasingly employed in wine production. Among the processes that use this technology are:

  • Chaptalization (the addition of substances to correct the profile of the grape must)
  • Clarification
  • Stabilization

The most common is electrodialysis, which can be used for removing potassium, calcium cations, and tartrate anions from wine. It’s useful in winemaking because it ensures the retention of flavor and aromas — important aspects of the sensory experience for wine drinkers. The technology can be flexible in removing whatever level might be desired to preserve the wine’s sensory properties..

Ionic Exchange

Another subtractive method for tartaric stabilization is using ionic exchange with resins. RWL Water said this process “reduces initial investment and costs less to operate than cold stabilization.” The process, which uses food-grade resins, works by passing the wine through an ionic exchange resin and then regenerating the wine with acid. This decanted wine is mixed with untreated wine.

This method offers reduced dilution of the treated juice and produces high-quality products. RWL Water said:

We pay particular attention to optimizing the sensory properties of the end product, carefully choosing suitable materials and resins.

Stabilization Regulations

There are some regulations governing stabilization, for example, European Commission Regulation No. 606/2009, which details oenological practices and restrictions for member nations. This includes a full outline of electrodialysis for stabilization of potassium hydrogen tartrate, and calcium tartrate and other calcium salts in wines, as well as guidelines for cation exchange.

Some winemakers and aficionados scoff at any type of stabilization, saying the treatments can affect the sensory pleasures inherent in wine.

Stephan Schindler, a Los Angeles wine importer, said:

Cold stabilization is like tossing out the baby with the bathwater. Perhaps you are left with an aesthetically flawless wine, but you are also left with a lesser wine.

But if your next bottle of wine has not been treated and happens to sparkle with diamonds, experts agree it need only be decanted properly to remove the tartrates.

Image by Neeta Lind, used under a Creative Commons license.

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