Wine Arcana

Concept

Tartrate stabilization

Also known as Tartrate stabilisation, Cold stabilization, Cold stabilisation

Tartrate stabilization reduces the likelihood that salts of tartaric acid will form visible crystals after a wine is bottled. Potassium bitartrate is the most familiar deposit, often appearing after chilling. Calcium tartrate can also form crystals, with different behaviour and different implications for treatment.

Tartrate crystals are harmless, but their appearance can concern drinkers or leave a gritty deposit in the glass. Winemakers can encourage precipitation before bottling, remove some of the dissolved ions that form the salts, or inhibit crystal growth. Cold stabilization is one method within this broader group of practices.

Why crystals form

Grapes supply tartaric acid and potassium. In wine, tartaric acid exists alongside electrically charged forms called bitartrate and tartrate ions. Their balance depends partly on pH. Under suitable conditions, potassium and bitartrate combine into a solid crystalline salt.

Temperature, alcohol, and the wine's wider composition affect how much salt can remain dissolved. Cooling can push a wine towards potassium bitartrate precipitation. Fermentation also changes the conditions as alcohol accumulates. A wine may be supersaturated, holding more dissolved salt than would remain at equilibrium, yet appear clear because crystals have not started growing.

Natural wine components can impede that growth. Polysaccharides, including yeast-derived mannoproteins, help explain why apparent stability can change as a wine matures or undergoes further processing. Stability assessed today may depend on inhibitors that later change or disappear.

Removing material or slowing growth

Traditional cold treatment chills the wine to encourage potassium bitartrate to crystallise in the cellar. Adding small seed crystals provides surfaces on which more salt can collect. The producer then separates the deposit from the wine. This uses refrigeration and tank time, so energy demand is part of the choice of method.

Electrodialysis takes a different chemical route. An electric field moves ions through selective membranes, reducing the concentrations available to form tartrate salts. The International Organisation of Vine and Wine (OIV) describes equipment designed to remove potassium, calcium, and tartrate ions under controlled conditions. Its account includes both potassium bitartrate and calcium tartrate stability as objectives.1. International Organisation of Vine and Wine, “Tartrate stabilisation by electrodialysis,” International Code of Oenological Practices, II.3.3.2.

Crystallisation inhibitors act on crystal formation or growth. Examples include carboxymethyl cellulose, potassium polyaspartate, and selected mannoprotein products. Their usefulness depends on the wine and the product. Interactions with proteins, colour, and filtration can influence the choice. An inhibitor that works against potassium bitartrate may offer little protection against calcium tartrate.

What a stability test establishes

Cold-stability tests expose a sample to specified conditions and look for evidence of potassium bitartrate precipitation. Other methods assess the potential for later instability. Test duration, temperature, and method affect the result, so “cold stable” describes performance under defined conditions. Blending or subsequent cellar treatments can change that performance.

Calcium tartrate needs separate attention. Its precipitation responds much less strongly to cooling and can be slow enough for deposits to appear months after bottling. The Australian Wine Research Institute cautions that ordinary cold treatment and simple cold tests are unreliable ways of resolving or predicting this problem.2. Australian Wine Research Institute, “Calcium and its unpredictable presence,” Australian & New Zealand Grapegrower & Winemaker 632 (September 2016), pp. 68–69.

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