Tartrate instability

First, laboratory testing is conducted to ascertain the stability of the wine. Like tests for protein stability, tests for determining stability and method for correcting instability vary from winery to winery. Berg (34) suggested that a wine stored at — 4° C for four days, without a bitartrate crystalline deposit, may be considered stable. The wines usually are allowed to warm to room temperature before test results are read. Absence of crystals indicates stability. A quantitative method, the concentration product (36), also can be used to evaluate tartrate stability. 

The temperatnre at which a wine becomes capable of dissolving bitartrate is a nseful indication of its state of supersatnration. However, in practice, enologists prefer to know the temperature below which there is a risk of tartrate instability. Maujean et al. (1985, 1986) tried to determine the relationship between saturation temperature and stability temperature. 

This is a completely different approach to forecasting tartrate instability, still one of the main problems in winemaking. 

Metatartaric acid instability accounts for initially surprising observations concerning wines treated in this way. One sample, stored at 0°C in a refrigerator, had no precipitation, while calcium tartrate precipitation occurred in another sample stored at 20-25°C when it was no longer protected due to hydrolysis of the metatartaric acid. 

With this in mind, its effectiveness has been compared to that of two other tartrate stabilization methods continuous contact cold stabilization and the addition of metatartaric acid (Table 1.21). This comparison was carried ont by measuring spontaneous crystallization after the addition of KHT (Section 1.6.4). The values obtained indicate the effectiveness of protective colloids, even if they do not necessarily correspond to the instability temperatnres. The addition of 15 g/hl of Mannostab to wine 2 and 25 g/hl... 

Proteins in must are a well-known cause of instability, affecting the clarity of white wines. When they precipitate, they cause protein casse , reported by Laborde as early as 1904. For many years, this was confused with white casse or copper casse . The turbidity or deposits characteristic of protein casse appear in the bottle, usually when wines are stored at high temperatures. They may also occur when tannin is leached into wine from the cork. Tartrate crystallization and flocculated proteins are responsible for the main problems with clarity in bottled white wines. 

The mechanisms behind this precipitation and ways of forecasting instability in wine are described elsewhere (Sections 1.5 and 1.6). Tartrate solubility is reduced by the presence of ethanol, but precipitation is partially inhibited by colloidal substances that coat the crystal nuclei and prevent them from growing. For this reason, wines, particularly reds, are likely to produce crystal deposits several months after fermentation. 

The command and control mechanism must take account of the particular instability of each wine so as to eliminate only the supersaturated fraction of potassium hydrogen tartrate and calcium salts. 

Moskvin AI, Khalturin GV, Gel man AD (1962) Determination of the composition and instability constants of citrate and tartrate complexes of americium(III) by the ion-exchange method. Radiokhim 4 162-166... 

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