**
Visual observation of crystallization and lowering of potassium concentration after six days at −4°C (Moine‐Ledoux et al., 1997).
Visual test: **, precipitation; –, no precipitation.
However, metatartaric acid is hydrolyzed in wine and loses its effectiveness, and adding tartaric acid may even facilitate potassium bitartrate crystallization. Under the same conditions, mannoproteins are stable and have a durable protective effect on tartrate crystallization. To demonstrate this difference, white wines treated with metatartaric acid or Mannostab and kept at 30°C for 10 weeks were then subjected to a cold test. Crystallization occurred in the sample treated with metatartaric acid, while the Mannostab sample remained stable (Table 1.22).
This new treatment process to protect wines from tartrate precipitation has been used experimentally in France since 1997 (Moine‐Ledoux and Dubourdieu, 2002). Treatment of white wine with mannoprotein preparations has been registered in the OIV International Code of Oenological Practice since 2001. Their findings led to authorization of the treatment of wines with mannoproteins from the degradation of yeast cell walls, by OIV in 2005 and by the EU (regulation 606/2009). This is intended to improve wine stability only with regard to its tartaric salts and/or its proteins in case of white and rosé wines. Doses should be determined in advance by the treatment supervisor. For some young red and rosé wines, a pre‐treatment with yeast hulls may be considered in order to increase the treatment's effectiveness. Mannoproteins constitute an alternative to cold stabilization, which consumes a lot of energy. It is also an alternative to metatartaric acid, which has a limited period of effectiveness (up to 18 months depending on the storage conditions of wine).
TABLE 1.21 Effect of Different Treatments on the Spontaneous Crystallization Temperature of Various Wines (Moine‐Ledoux et al., 1997)
| Stabilization treatments | Wine 1 (°C) | Wine 2 (°C) |
|---|---|---|
| Control | −10 | −11 |
| Mannostab (15 g/hl) | −21 | −18 |
| Mannostab (25 g/hl) | −31 | −13 |
| Continuous contact cold stabilization | −28 | −17 |
| Metatartaric acid (10 g/hl) | −40 | −40 |
Wine 1, 1996 Entre Deux Mers; Wine 2, 1996 white Bordeaux.
TABLE 1.22 Influence of Keeping a White Wine Supplemented with Metatartaric Acid or Mannostab at 30°C for 10 Weeks on the Tartrate Stability, Estimated by the Decrease in Potassium Concentration After Six Days at −4°C (Moine‐Ledoux et al., 1997)
| Δ(K+) mg/l, after six days at −4°C | |
|---|---|
| Control | 200 |
| Metatartaric acid (10 g/hl) | 260 |
| Mannostab (25 g/hl) | 0 |
1.7.8 The Use of Carboxymethylcellulose
CMC is a polysaccharide. Like metatartaric acid and mannoproteins, its polymer structure gives it protective colloid characteristics. It is obtained by preferential etherification of the primary alcohol functions of glucopyranose units (Figure 1.23) linked by β‐1,4‐glycosidic bonds. CMC is therefore characterized partly by the degree of etherification of its alcohol functions, known as the degree of substitution (DS), and partly by its degree