South Africa Wine Technical Yearbook 2025

NOVEMBER

SHUTTERSTOCK

Tackling calcium crystals in wine By Sami Yammine* Q&A

Q: Do LAFFORT® bentonites contribute to calcium concentrations in wine? A: No, in-house trials revealed that, when used at recommended doses, they do not increase the calcium content of wines. Q: How exactly does pH affect CaT formation? A: Tartaric acid exists in three forms in wine: H 2 T (undissociated tartaric acid), HT – (bitartrate) and T² – (tartrate). 1 Their proportions depend on pH. At an average wine pH (around pH 3.6), the bitartrate form typically dominates, and it is this form that binds with potassium to form potassium bitartrate (KHT), also known as potassium hydrogen tartrate. However, tartrate ions (T² – ) increase in concentration as the pH increases. 3 This is the form that typically binds with calcium to form CaT. So, theoretically, at pH 3.2, a wine with 60 mg/L calcium may be stable. However, at pH 3.8, the same concentration could be problematic due to the increased availability of tartrate ions that the calcium can bind to. This is also why one cannot rely solely on the calcium concentration to determine whether a wine will become unstable. In the same breath, one also cannot assume that a low pH equals a CaT stable wine due to low tartrate concentrations, since CaT instability has been reported in sparkling wines. The problem is multifactorial. Q: Can CaT stay in solution like KHT? A: Yes, up to a point. Once the CaT in the wine reaches supersaturation, it can potentially (in the absence of inhibitors) start to nucleate and crystallise. Calcium tartrate is approximately 10 times less soluble than KHT (0.525 g/L ,2 compared to 5.2 g/L 5 , in water at 20°C). However, its nucleation is slower and is not significantly

Calcium instability in wine is a complex issue influenced by various factors. Understanding these factors and the tools available to address them is essential for producing stable, high-quality wines. In this article, Dr Sami Yammine answers the most significant questions related to calcium crystals in wine and provides guidance on how to prevent them. Q: Calcium tartrate (CaT) crystals are showing up more often in bottled wine. Is this a new problem? A: No, it’s not new. But the frequency has increased. As a result, there’s more discussion, research and innovation around the topic, both in academic circles and among oenological product suppliers. Q: What’s causing this rise in CaT instability? A: Climate change appears to play a role. 1,2 Warmer conditions and reduced rainfall create stress in the vine, altering the grape composition. Some key changes that contribute to instability include: • Higher calcium concentrations in juice. • Higher sugar levels, resulting in higher final alcohol. Q: Are there other sources of calcium in wine, apart from the grapes? A: Yes, several winemaking practices and materials can add calcium: • Use of low-purity casein. • Certain poor-quality calcium-based bentonites at high doses. • Calcium carbonate for deacidification. • Wine stored in unsealed cement tanks. • Vineyard inputs containing calcium or carbonate. • Higher pH levels. • Lower malic acid.

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TECHNICAL YEARBOOK 2025