industrial preparation (Mannostab™) has been purified from yeast cell wall mannoprotein. It is a perfectly soluble, odorless, flavorless, white powder. This product has been quite effective (Table 1.20) in preventing tartrate precipitation in white wine samples taken before the normal cold stabilization prior to bottling. Initial results show that Mannostab inhibits potassium bitartrate crystallization at doses between 15 and 25 g/hl. However, in certain wines in Table 1.20 (1996 white Bordeaux and 1996 white Graves), larger quantities apparently reduced the stabilizing effect. A similar phenomenon has been reported with a protective colloid used to prevent protein precipitation (Pellerin et al., 1994). The dose of Mannostab necessary to stabilize a wine must be determined by preliminary testing. It is very clear that the use of excess amounts of this additive is ineffective.
The addition of this product could replace current stabilization methods (Moine‐Ledoux et al., 1997). With this in mind, its effectiveness has been compared with that of two other tartrate stabilization methods: continuous contact cold stabilization and the addition of metatartaric acid (Table 1.21). This comparison was carried out 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 temperatures. The addition of 15 g/hl of Mannostab to wine 2 or 25 g/hl to wine 1 produced the same spontaneous crystallization temperature, i.e. a stability comparable to that obtained by continuous cold stabilization (Table 1.21). The addition of metatartaric acid, however, considerably reduced the crystallization temperature.
TABLE 1.20 Tartrate Stabilization of Various Wines by Adding Mannostab
| Wines | Mannostab (g/hl) | |||||
|---|---|---|---|---|---|---|
| 0 | 15 | 20 | 25 | 30 | ||
| 1996 Blanc de Blanc | Visual test | ** | – | – | – | – |
| Δ(K+) (mg/l) | 52 | 72 | 17 | 0 | 0 | |
| White vin de table | Visual test | ** | – | – | – | – |
| Δ(K+) (mg/l) | 104 | 53 | 33 | 0 | 0 | |
| 1996 White Bordeaux | Visual test | ** | – | – | – | – |
| Δ(K+) (mg/l) | 62 | 21 | 0 | 0 | 21 | |
| 1996 White Graves | Visual test | ** | ** | – | – | – |
| Δ(K+) (mg/l) | 155 | 52 | 0 | 0 | 62 | |
| 1996 White Bordeaux | Visual test | ** | – | – | – | – |
| Δ(K+) (mg/l) | 51 | 0 | 0 | 0 | 0 | |
| 1996 Entre Deux Mers | Visual test | – | – | – | – | – |
| Δ(K+) (mg/l) | 52 | 0 | 0 | 0 | 11 |
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)
