Technical Yearbook 2024

MAY

Enartis

Calcium tartrate instability By Carien Coetzee

Calcium-induced instability is a most insidious problem in bottled wines mainly due to the unpredictable and slow formation of crystals, which usually do not come out of solution for some time after bottling and often after commercial release. Calcium instability Forms of tartrate instabilities Tartrate instability can manifest as the precipitation of two salts: potassium bitartrate (KHT) and calcium tartrate (CaT). Even though both are tartrate salts, the two salts form under very different conditions and at different rates. 1 Types of calcium instabilities The most common manifestation is in the form of crystalline calcium L -tartrate. Other less common occurrences of calcium instability are calcium DL -tartrate and calcium oxalate. When problems involving calcium DL -tartrate did

occur, the investigation revealed that the instability resulted from using DL -tartaric acid as an acidulant. Oxalic acid is present in some commercial batches of L -tartaric acid and can be responsible for calcium oxalate instability. 1 Calcium tartrate crystal morphology Calcium tartrate forms crystals that are very different from potassium bitartrate and, therefore, easily recognisable under the microscope. Deposits of calcium tartrate usually appear as colourless or white, bipyramidal or rhomboid crystals. 1 In some cases, co-deposits are also present, such as phenolic and protein material, quercetin crystals, or yeast cells. 1 Calcium tartrate crystal formation and main influencing factors Calcium tartrate deposits are a most insidious problem in bottled wines because the kinetics of crystallisation are very

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TECHNICAL YEARBOOK 2024