Technical Yearbook 2024

tartrate unstable may prove impossible to stabilise even if kept at low temperatures for long periods. 1 Therefore, cold stabilisation cannot be used as a reliable method to remove the threat of instability by precipitation. However, the use of low temperatures may, in some cases, accelerate the sedimentation kinetics of calcium tartrate formation. For instance, it is applied during the calcium precipitation test, where seeding initiates crystal formation. Protective colloids Protective colloids are generally ineffective in preventing calcium tartrate crystal formation. 3 However, certain colloids can partially modify the shape of the crystal. 3 Metatartaric acid seems to be effective in inhibiting crystal formation. However, its effects are not stable over time as it undergoes hydrolysis, leading to increased acidity due to the release of tartaric acid. 5 Consequently, metatartaric acid loses its inhibitory effect over time, depending on wine storage temperature, with more rapid hydrolysis occurring at higher temperatures. Exchange resins and electrodialysis If specific for bivalent cations, ion exchange resins can improve calcium tartrate stability by removing calcium and, indirectly, by lowering the pH. 3 Electrodialysis can reduce the concentration of calcium and tartaric acid, two critical factors contributing to calcium instability. Both techniques are not specific to calcium tartrate stabilisation but can help reduce the risk of calcium tartrate precipitation. 3 Crystallisers/seeding Seeding (addition of crystallisation nuclei) can initiate and accelerate the natural calcium tartrate precipitation, thus making the crystallisation process predictable and controlled. This technique relies on the availability of high quality, micronised calcium tartrate crystals, which provide millions of crystallising germs and help overcome the main limiting factor of the crystallisation process: germ formation. The added germs can grow and form larger crystals without the need to cool the wine and without being hindered by the presence of suspended particles, making it suitable for use in conjunction with clarification processes. It should be noted that potassium bitartrate precipitation does not induce calcium tartrate precipitation. The advantage of this treatment is that the added micronised calcium tartrate nuclei are insoluble and not consumed by microorganisms. With its effectiveness, ease of use, and respect for the wine’s sensorial properties, adding micronised calcium tartrate can be a suitable solution to reduce the risk of calcium tartrate instabilities. Crystallisation inhibitors As mentioned earlier, many components in wine can greatly enhance a wine’s holding capacity for calcium tartrate.

Conclusion The occurrence of precipitated calcium tartrate in wine is becoming more frequent worldwide. The temperature independence of the crystal formation, the absence of a reliable correlation between calcium concentration and calcium tartrate instability, and the lack of reliable stabilising procedures and tests to predict the instability make calcium instability a serious problem. The monitoring and management of potential calcium instabilities has yet to become part of the routine activity of many oenologists. Scrupulous elimination of sources of calcium from viticultural and winemaking procedures appears to be the most practical method of avoiding calcium instability problems. However, inhibiting calcium tartrate precipitation is arguably the most crucial preventative factor. 6 This article was originally published in January 2023 by Sauvignon Blanc South Africa on their website. It is republished in WineLand with permission from Sauvignon Blanc South Africa.  levels in sparkling wines than table wines, which may account for the frequent occurrence of calcium tartrate instability in sparkling wines. 7 References https://www.wineland.co.za/calcium-tartrate-instability/ Inhibitory compounds such as gluconic acid, malic acid, citric acid, potassium and magnesium may slow or even prevent nucleation by binding with free calcium or tartrate, lowering the supersaturation. Alternatively, inhibitors may attach to the soluble calcium tartrate aggregates and block critical nucleus formation. Malic acid is highly inhibitory to the crystallisation process. 1 Wines that undergo malolactic fermentation become more vulnerable to calcium tartrate precipitation due to the resulting pH increase and because an efficient calcium tartrate crystallisation inhibitor (malic acid) is replaced by a less efficient one (lactic acid). This means that a sparkling wine or a full-bodied white wine containing a sub-critical concentration of calcium in the presence of malic acid can become unstable following malolactic fermentation. Typically, in these wines, the characteristic delay in precipitation of calcium tartrate results in instability, which does not show until sometime after the pH change. 6 Other natural wine components, like the polyuronic acids of grape pectins, are also efficient inhibitors of calcium tartrate crystal growth. These macromolecules are at lower

For more information, contact Carien Coetzee at carien@basicwine.co.za.

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TECHNICAL YEARBOOK 2024