Determination of the temperature of saturation, of the field of supersaturation and of the « rules » of stability towards the calcium tartrate in wines

Abstract

This publication describes a methodology which allows to find the temperature of saturation of wine in regard to calcium tartrate (TCa), or TSca, and the field of supersaturation of wine in regard to this salt (ΔTca). The values found allow to show that the wine can bear a degree of supersaturation high (8 - 12°C) (dTca = TSca - Tstocking) in regard to TCa without letting crystals appear, even during very long storage. The least solubility of the TCa in regard to potassium bitartrate (THK) allows to explain these differences between the two salts which have been studied. The field of supersaturation (ΔTca = TSca - TCsca) of 12,5 p. cent vol. rosé wine towards this salt has been quantified. It's in the region of 42 to 44°C, whereas a hydroalcoholic solution of the same alcoholometric range and of appreciably equivalent pH has a field of supersaturation in the order of 35°C. The share of the width of the field of supersaturation of wines owed to the « colloids » can be estimated to a quarter, indeed a third of the entire width of the field of supersaturation, the rest being owed to the natural characteristic/ability of the hydroalcoholic solutions to supersaturate towards this salt. A scale of stability in regard to the risks of appearance of crystals of TCa in the wine has been determined for short storage at - 2°C and long storage in a cellar thermoregulated at 10 - 12°C: TSca limit ≤ 26-27°C white and rosé wines, white VDN ; TSca limit ≤ 35°C red wines (1 to 2 years runback). In the case of wines not « entiched » in exogenous calcium (and/or TCa) and with « standard » initial contents (40 to 140 mg/l) the risks of appearance of TCa crystals after tartaric balancing in regard to THK are generally small.