Metatartaric acid

Magnesium trisilicate Malic acid Metatartaric acid Methyl p-hydroxybenzoate Micro crystalline cellulose Micro-crystalline wax... 

Other methods to achieve bitartrate stability, rarely used in the North Coast, are addition of metatartaric acid, electrodialysis, reverse osmosis, and ion exchange. Concern with potential bitartrate instability varies from winery to winery. Some enologists prefer to keep the processing of wine to a minimum. They rely solely on cool fermentation and winter storage temperatures to precipitate excess bitartrates. They trust their customers will overlook any additional bitartrate crystals that precipitate out in bottled wines. 

Section V Stabilising Agents Recommended none are recommended Tolerated citric, tartaric, malic, ascorbic, fiimaric acids from nonsynthetic sources according to BATF standards. Low temperatures for tartrate stabilisation (cold stabilisation). Flash pasteurisation with technical justification Prohibited potassium ferrocyanide, synthetic citric acid, metatartaric acid, sorbic acid and sorbates... 

Use of Metatartaric Acid for Stabilization of Tartrate Salt Precipitation. 148... 

Work has been done to find whether the very expensive treatment of wines with artificial cold could be advantageously replaced by the addition of inhibitors of the crystallization process of tartrate salts such as metatartaric acid, yeast mannopro-teins or carboxymethylcellulose (CMC). Such inhibitors indeed increase the width of the supersaturation field of both KHT and TCa in the wine, thus delaying tartrate salt precipitation in the bottle. Metatartaric acid is currently the product most widely used for this purpose, though its efficacy is low as this compound does not remain stable over time. Yeast mannoproteins possess stabilizing properties, which result in the spontaneous improvement of protein and tartaric salt stability, as can be... 

Besides these two systems, a new separation technique, electrodialysis, is also applied to the bitartrate stabilization of wine (Section 12.5). The use of ion-exchange resins is also permitted in certain countries, including the USA (Section 12.4.3). Finally, it is possible to prevent the precipitation of these salts by adding crystallization inhibitors, such as metatartaric acid or yeast mannoprotein extracts (Section 1.7.7), or carboxymethylcellnlose (Section 1.7.8). 

The spontaneous crystallization temperature of each sample of treated wine (Table 1.16) was also determined using the same procedure. Examination of the results shows that a wine filtered on a 10 Da Millipore membrane, i.e. a wine from which all the colloids have been removed, has the lowest value for the supersaturation field (Tsat - Tcso), closest to that of the model dilute alcohol solution. Therefore, the difference between the results for this sample and the higher values of the supersaturation fields of fined samples define the effect of the protective colloids. It is interesting to note that the sample treated with metatartaric acid had the widest supersaturation field, and cold stabilization was completely ineffective in this case. This clearly demonstrates the inhibiting effect this polymer has on crystallization and, therefore, its stabilizing effect on wine (Section 1.7.6). Stabilization by this method, however, is not permanent. 

O Metatartaric acid Gelatin tannin Gum arable V 0.22 im filter... 

Metatartaric acid is currently the prodnct most widely used for this purpose. Carboxymethylcel-lulose (Section 1.7.8) and mannoproteins extracted from yeast (Section 1.7.7) have also been snggested as stabilizers. 

Metatartaric acid is a polyester resulting from the inter-molecular esterification of tartaric acid at a legally imposed minimum rate of 40%. It may be used at doses up to a maximum of 10 g/hl to prevent tartrate precipitation (potassium bitartrate and calcium tartrate) (Ribereau-Gayon etal., 1977). 

When tartaric acid is heated, possibly at low pressure, a loss of acidity occurs and water is released. A polymerized substance is formed by an esterification reaction between an acid function of one molecule and a secondary alcohol function of another molecule. Tartaric acid may be formed again if the metatartaric acid is subjected to hydrolysis. In reality, however, not all of the acid functions react (Figure 1.18). 

The esterification number of different metatartaric acid preparations may be determined by acidimetric assay, before and after saponification. Table 1.18 shows the importance of the preparation conditions in determining this value. 

Metatartaric acid is by no means a pure product solutions are slightly colored and oxidizable. They may contain oxaloacetic acid, but the main impurity is pyruvic acid, representing 1-6% by weight of the metatartaric acid, according to the preparation conditions (Table 1.18). It is, therefore, important to correct the esterification number to compensate for this impurity. The formation of... 

Table 1.18. Detailed analysis of various metatartaric acid preparations (Peynaud and Guimberteau, 1961)...

There are many laboratory tests for assessing the effectiveness of a metatartaric acid preparation. Table 1.19 presents an example of a procedure where a saturated potassium bitartrate solution is placed in 10 ml test tubes and increasing quantities of metatartaric acid preparations with different esterification numbers are added. This inhibits the precipitation of potassium bitartrate induced by adding 1 ml EtOH at 96% vol and leaving the preparation overnight at 0°C. Only 1.6 mg of a preparation with an esterification number of 10 is... 

The fact that metatartaric acid solutions are unstable has a major impact on their use in winemaking. They deteriorate fairly rapidly and are also sensitive to temperature. Hydrolysis of the ester functions occurs, accompanied by an increase in acidity. After 20 days at 18-20°C, there is a considerable decrease in the esterification number (Figure 1.20). Under experimental conditions, total hydrolysis of a 2% metatartaric acid solution took three months at 23°C and 10 months at 5°C. Consequently, it is necessary to ensure that metatartaric acid solutions for treating wine are prepared just prior to use. 

Number Esterification number Metatartaric acid added in each tube (in mg) ... 

Fig. 1.20. Hydrolysis rate of two qualities of metatartaric acid in 2% solution (f in the esterification number (Ribdreau-Gayon et al., 1977)...

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. 

The conditions for using metatartaric acid depend on its properties. A concentrated solution, at 200 g/1, should be prepared in cold water at the time of use. As metatartaric acid is strongly hygroscopic, it must be stored in a dry place. 

Metatartaric acid is added after fining, as there is a risk of partial elimination due to flocculation. It is particularly affected by bentonite and potassium ferrocyanide treatments. Although there... 

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... 

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 6 days at —4°C (Moine-Ledoux et al, 1997)...

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