Winetech Technical Yearbook 2022

AUGUST

CALCIUM TARTRATE INSTABILITY OF WINE

TARTRATE INSTABILITY OF WINE IS USUALLY ASSOCIATED WITH THE APPEARANCE OF CREAM OF TARTAR OR POTASSIUM BITARTRATE CRYSTALS, ALSO KNOWN AS WINE DIAMONDS, IN CHILLED WHITE WINES. DUE TO DIFFERENT FACTORS CALCIUM TARTRATE INSTABILITY HAS HOWEVER BECOME AN ISSUE, WHICH NEEDS THE NECESSARY ATTENTION.

BY CHARL THERON

THE FIXED ACID CONCENTRATION OF WINE has decreased and the resulting pH has gradually risen due to global warming. The calcium concentration of grapes is directly linked to the alkalin ity of the soil and an increase in the latter will also cause higher grape concentrations. Calcareous soils will consequently increase the calcium availability to the vine. Nitrates will also favour the calcium uptake, while some metals like potassium and magne sium can decrease it. Calcium is essential for all plants namely as messenger under stress conditions and a component of cell walls and membranes. It is mainly stored as Ca-pectate in the cell wall and as Ca-oxalate in the cell vacuole. Between 75 - 90% of the calcium concentration is already in the grape berries before veraison. Calcium tartrate crystals differ from potassium bitartrate crystals and can easily be identified microscopically. Its water solubility at 0,53 g/L at 20°C is much lower than the 5,7 g/L of potassium bitartrate. It crystallises very slowly, because the nu cleation phase requires much energy to form the crystal nucle us. Unlike potassium bitartrate it is also not much affected by a temperature drop. The pH plays an important role in Ca-tartrate stability because the equilibrium of the different tartrate ions in the wine is influenced by it. The percentage of the T -2 is higher at higher pH, which will consequently favour the calcium tartrate formation. Malic acid and magnesium hinder the formation of calcium tartrate. The calcium tartrate stability is presently often

based on the calcium concentration of the wines, with 80 mg/L for white and rosé, and 60 mg/L for red wines seen as the safety values. This research was however based on the pH-values of that time, which have increased since then. This can be clarified by the following example: A red wine with a calcium concentration of 60 mg/L and a pH of less than 3,5 will not precipitate calcium tartrate, but at a pH of 3,7 or higher precipitation is likely. It is however necessary to determine the calcium tartrate sta bility of wine. It is important to utilise the three factors influenc ing calcium tartrate stability, namely pH, calcium and tartrate concentration to develop this. Contrary to the bitartrate tartrate stability test by conductivity, it is of no use for calcium tartrate stability evaluation. The recommended test is based on the cal cium concentration analysis of the wine before and after 400 g/ hL micronised calcium tartrate was added to the wine which was kept at 0° C for 24 hours. The difference between the initial and final concentration is an indication of stability as indicated in ta ble 1.

TABLE 1. Calcium tartrate stability status of wine. Difference in Ca-concentration Before and after (mg/L)

Stability status

<15

Stable

15 - 25

Slightly unstable

>25

Unstable

If a wine is found to be Ca-tartrate unstable, some stabilising ac tion has to be implemented. The use of cold treatment or pro tective colloids are however not effective. Cooling accelerates the Ca-tartrate precipitation only slightly. Protective colloids do not inhibit the formation of the Ca-tartrate crystal although it adjusts its shape. Metatartaric acid protective ability is effective, but due to the hydrolysis of the latter over time the protection is only temporary. The use of ion exchange and electrodialysis seem to be more effective. If ion exchange resins, with a bivalent ion like Ca removal and a resulting lowering of the pH are used, the Ca-tartrate stability will be improved. The effectiveness of elec trodialysis can be due to the removal of both Ca and tartrates as the two main components of Ca-tartrate crystals. Both methods are not specific for Ca-tartrate stability, but will at least dimin ish the potential precipitation. Another technique is the use of tartrate salt crystallisers, like synthetic tartaric acid (DL- or ra cemic tartaric acid) or L(+) calcium tartrate, which accelerates the natural crystallisation of Ca-tartrate if it is above the stability concentration level. Concerns exist about the synthetic tartaric acid, regarding its health influence and reaction time. The use of micronised L(+) calcium tartrate at a dosage level of 50 g/hL seems to be effective (Quinterno et al. ). REFERENCE https://www.wineland.co.za/calcium-tartrate-instability-of-wine/

Ca-tartrate appears as fine, white crystals at the bottom of bot tles and tanks with unstable wines.

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WINETECH TECHNICAL YEARBOOK 2022