Tartrate precipitation

Wucherpfennig, K. 1975. The inhibition of tartrate precipitation in grape juice concentrate by means of electrodialysis. International Federation of Fruit Juice Producers. Scientific-Technical Commission Report 13, pp. 73-117. 

Another method of acid amelioration, used to avoid water amelioration, is the addition of calcium salts for the purpose of substituting calcium for potassium ions. The resulting calcium bitartrate salts, being less soluble, increase the precipitation of bitartrate. This raises technical problems, one being that if the malo-lactic fermentation should take place subsequently, the wine may contain insufficient acidity of any kind. Another is that calcium tartrate precipitates slowly and in more finely divided form, often causing persistent hazes that are hard to remove. Often, too, this precipitation is delayed, leading to the presumption that the wine is tartrate stable. Only after it is bottled, the brilliant and supposedly stable wine may develop a delayed calcium tartrate haze and even a deposit. The calcium salt method in a refined form is used considerably in Germany but rarely here. 

Rodriguez-Clemente, R., Correa-Gorospe, 1. (1988). Structural, morphological and kinetic aspects of potassium hydrogen tartrate precipitation from wines and ethanolic solutions. Am. J. Enol. Vitic., 30, 169-179. 

Vernhet, A., Dupre, K., Boulange L., Cheynier V, Pellerin R, Moutounet M. (1999a). Composition of tartrate precipitates deposited on stainless steel tanks during the cold stabilization of wines. Part I wMte wines. Am. J. Enol. Vitic., 50, 391-397. 

In the resolution procedure, racemic trans-dach (60 g) is dissolved in 200 mL of water along with 20 g of the appropriate (d or l) tartaric acid and 40 mL of acetic acid. The resulting dach-tartrate precipitate is collected and recrystallized two to three times from hot water. The resolved dach isomer is then liberated by treating the salt with excess 20% NaOH (aq) and extracting the free base into CHClj. 

A.Vernhet, K. Dupre, L. Boulange-Petermann et al.. Composition of Tartrate Precipitates During... Cold Stabilization of... White Wines, Am. J. Enol. Viticult. 50(4), 391-397 (1999) Red wines, ibid., 398 03. 

Wurdig and Muller (1980) were the first to make use of the capacity of must and wine to act as electrolytes, i.e. solntions condncting electricity, to monitor tartrate precipitation. Indeed, dnring precipitation, potassinm bitartrate passes from the dissolved, ionized state, when it is an electrical conductor, to a crystalline state, when it precipitates and is no longer involved in electrical conductivity ... 

The conductivity meter cell is subjected to an alternating current. The frequency is set at 1 kHz for the standardized solution (KCl = 0.02 m) and wine, to avoid polarizing the electrodes. A conductivity meter is used for continuous monitoring of tartrate precipitation in wine (see Section 1.6.4, Figure 1.16). 

Stabilizing wines to prevent precipitation of calcium tartrate is not easy, as the crystallization of potassium bitartrate does not indnce that of calcium tartrate, despite the fact that these two salts should logically syncrystallize as they have the same crystal systems. On the contrary, crystallization of TCa may induce that of KTH. The prevention of calcium tartrate precipitation is further complicated by the fact that the solubility of TCa (Postel, 1983) is not very temperature-sensitive. Thns, TCa is hardly three times more soluble at 20°C than at —4°C. 

Furthermore, according to Abgnegnen and Boulton (1993), althongh the crystallization kinetics of TCa should be higher than those of KTH, the time required for spontaneous nucleation of TCa is much longer. It is therefore easier to nnderstand why calcium tartrate precipitation generally occurs in wine after several years aging. 

In order to avoid the risk of calcinm tartrate precipitation, the saturation temperatnre of white, rose and vins doux naturels must be lower than 26° C to ensure that calcium tartrate deposits will not be formed if the wine is kept at 2°C for one... 

In the processes described above, tartrate precipitations are prevented by eliminating the corresponding salts. It is also possible to envisage the addition of crystallization inhibitors. 

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). 

Furthermore, the same phenomenon occurs in wine and is detrimental to the treatment s effectiveness. Rib6reau-Gayon et al. (1977) demonstrated that stability in terms of tartrate precipitations may be considered effective for the following lengths of time, depending on temperature ... 

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. 

Yeast mannoproteins were first fonnd to have a certain inhibiting effect on tartrate crystallization in a model medium by Lubbers et al. (1993). However, these experiments used mannoproteins extracted by heat in alkaline buffers, under very different conditions from those accompanying the spontaneons enzymic release of mannoproteins dnring aging on the lees. Furthermore, the effectiveness of mannoproteins extracted by physical processes in preventing tartrate precipitation has not been established in most wines, despite demonstrations in a model medium. 

An industrial preparation (Mannostab ) has been purified from yeast-wall mannoprotein. It is a perfectly soluble, odorless, flavorless, white powder. This product has been qnite effective (Table 1.20) in preventing tartrate precipitation in... 

This new treatment process to protect wines from tartrate precipitation has been used experimentally in France since 1997 (Moine-Ledoux and Dubourdieu, 2002). Mannoprotein preparation treatment of white wine is registered in the OIV... 

It should also be noted that the purified manno-protein preparation obtained by digesting yeast cell walls contains another protein fraction that has a protective effect on tartrate precipitation (Moine-Ledoux et al., 1997) (Section 1.7.7). It is perfectly possible to envisage using an industrial preparation of this protective colloid in the near future to stabilize white wines and prevent tartrate precipitation. 

Involvement of protective colloids in clarification problems and the tartrate precipitation mechanism... 

Crystalline tartrate precipitation may be assimilated to colloidal phenomena (Section 1.5.1). Indeed, the natural colloids in wine, particularly mannoproteins (1.7.7), have a protective effect that inhibits tartrate precipitation, even when concentrations are higher than the solubility product. This phenomenon is particularly marked in red wines. 

Most wines certainly contain mucilaginous substances that act as protective colloids mannoproteins. Their existence is demonstrated by the elimination of the protective effect after fine ultrafiltration or dialysis. This phenomenon is well known in red wines, where colloidal coloring matter and tannins inhibit tartrate precipitation. It also exists in white wines and may be attributed to neutral polysaccharides (gum). According to the desired result, these substances may either be eliminated by fine filtration (e.g. to facilitate tartrate stabilization) or, on the contrary, protective colloids such as gum arabic may be added to a clear wine just before bottling to compensate for insufficient natural protection. 

Facilitating tartrate precipitation simply centrifuging a wine may canse the precipitation of potassium hydrogen tartrate. This may be due to the elimination of protective colloids or the effects of violent agitation. Furthermore, centrifugation has been suggested as... 

Refrigeration is widely used for stabilization to prevent tartrate precipitation. This treatment alone may be adequate to ensure the stability of red wines. However, if bentonite is not used to treat white wines, prior heating is necessary to prevent protein precipitation. In some countries, equipment capable of applying both heat and cold is used. These processes give satisfactory results in stabilizing white wine with a low iron content, as they have only a limited effect on ferric casse. 

This chapter also describes several physicochemical treatments based on electrical charges in solutions. Ion exchange and electrodialysis are mainly used to prevent tartrate precipitation. These techniques are much more controversial than purely physical methods. If they are not properly used, they may produce unacceptable changes in a wine s chemical composition. This is why they are not legally permitted in all wine growing countries. Their utilization must be carefully controlled by legislation. 

One effect of heating is to dissolve crystallization nuclei, which are necessary for crystals to grow and precipitate. New wine is a supersaturated tartrate solution. The precipitation of tartrates, however, requires the presence of submicroscopic nuclei that are the starting point from which molecules build up into crystals (Section 1.5.1). Heating wine, especially when it is already in the bottle, may be sufficient to stabilize it and prevent tartrate precipitation. 

Cold stabilization is mainly used to prevent tartrate precipitation. As there are effective, less expensive treatments are available for other problems. 

The various processes using cold temperatures to prevent tartrate precipitation have been described elsewhere (Section 1.7.1 to 1.7.5). There are three major procedures ... 

Hydrogen, sodium and magnesium resins may be nsed to removed K+ and prevent tartrate precipitation. These different forms are obtained by the regeneration operation that consists of circnlating either an acid or a saline solution (sodinm or magnesium chloride) through the column to saturate the sulfonate or acid radicals (Figure 12.2) in the resin with H+, Na+ or Mg + ions. 

In both of the preceding instances, it is recommended that the cation exchange treatment is applied to approximately 10-20% of the total volume of the wine. The treated wine is then mixed into the rest. It is also advisable to cold-stabilize the wine prior to ion exchange treatment to enhance protection from tartrate precipitation. 

Modeling this phenomenon over a 4-honr period makes it possible to assess the theoretical drop in condnctivity over an unlimited period. The test resnlts, therefore, indicate the final condnctivity valne at which the wine no longer presents a risk of tartrate precipitation. The drop in condnctivity reqnired for the wine to be stabilized is monitored using an automatic system controlled by a PC (Escndier et al., 1998). 

Virginie Moine-Ledoux for her work on the use of yeast mannoproteins in preventing tartrate precipitation (Chapter 1), as well as the stabilization processes for protein casse (Chapter 5)... 

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