Tartrate stabilization

Ramifications of production of wine and related products are depicted in Eigure 1 (23). Certain operations are required, unique, and irreversible in order to produce certain types of wine, eg, oxidation for sherries. Other operations such as clarification and tartrate stabilization are similar for all wines. 

New enological technologies aim to lower volatile acidity, enhance sugar content in must in cool climates and vice versa reduce the alcohol content of wines from hot climates, modify pH, cations, anions and acidity to achieve tartrate stability, complement traditional ageing in oak barrels with the use of small oak wood particles and most recently, extract phenolic compounds by a countercurrent chromatography process from wine to diminish or enrich tannins in red wines. 

A further consideration of the change in pH is the affect on tartrates. As the pH reaches 3.56-3.60 (the midpoint between the two pKa s for tartaric acid) the precipitation of potassium bitartrate is increased (65, 66). This decrease in tartrate concentration in the wine is beneficial in the overall process of achieving tartrate stability. Although the pH of the 1972 wines did not reach this level, the pH does reach and exceed this range in some years (64). 

The term wine refers to the natural beverage produced from the juice of sound and ripe grapes, in strict accordance with federal and state regulations. The stabilization principles discussed will have equal application to fruit wines in general except for tartrate stabilization since tartaric acid, the primary organic acid of grapes, is not found in any other fruits commonly used in winemaking. 

Berg, H. W., Keefer, R. M., Analytical Determination of Tartrate Stability... 

Range Tartrate Stability, Amer. J. Enol. Viticult. (1963) 14, 43-51. 

Tartaric Acid. Quantitative measures of total tartrate are useful in determining the amount of acid reduction required for high acid musts and in predicting the tartrate stability of finished wines. Three procedures may be used. Precipitation as calcium racemate is accurate (85), but the cost and unavailability of L-tartaric acid are prohibitive. Precipitation of tartaric acid as potassium bitartrate is the oldest procedure but is somewhat empirical because of the appreciable solubility of potassium bi-tartrate. Nevertheless, it is still an official AO AC method (3). The colorimetric metavanadate procedure is widely used (4, 6, 86, 87). Tanner and Sandoz (88) reported good correlation between their bitartrate procedure and Rebeleins rapid colorimetric method (87). Potentiometric titration in Me2CO after ion exchange was specific for tartaric acid (89). 

Although early ED tests for tartrate stabilization of wines had been performed by Paronetto (1941), more systematic experiments were carried out in the 1970s (Audinos et al., 1979 Paronetto et al., 1977 Wucherpfennig and Krueger, 1975) and led to the automatic method and device for tartaric stabilization of wines developed by Escudier et al. (1995) at the French National Agronomic Research Institute (INRA) in cooperation with Ameridia (Moutounet et al., 1997). 

Moutounet, M., Saint-Pierre, B., Battle, J.L., and Escudier, J.L. 1997. Tartrate stabilization Principle and description of the procedure. Revue Frangaise d Oenologie 162, 15-17. 

Paronetto, L., Paronetto, L., and Braido, A. 1977. Some tests on tartrate stabilization of musts and wines by electrodialysis. Vignevini 4, 9-15. 

Riponi, C., Nauleau, F., Amati, A., Arfelli, G., and Castellari, M. 1992. Electrodialysis. 2. Tartrate stabilization of wines by electrodialysis. Revue Frangaise d Oenologie 137, 59-63. 

Clarification was by racking, fining, and filtration. With the general use of water, tartrate stabilization was not a major problem. The cold winters also facilitated precipitation of excess tartrates. 

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. 

Pilone, B.F. Berg, H.W. Some Factors Affecting Tartrate Stability in Wines, ... 

The solubility of potassium acid tartrate (KHT) decreases with increased ethanol, and the increase in ethanol during secondary fermentation may cause KHT crystals to form. Young base wines, which have been tartrate stabilized by refrigeration only, often form crystals after secondary fermentation. Wines that have been refrigerated and ion exchanged are more resistant. 

Table 5.2 Tartrate stabilization of various white wines by adding Mannostab as determined by visual observations of potassium bitartrate crystallization within six days at —4°C (redrawn with permission from Moine-Ledoux et al. 1997)...

The fact that the phenomenon of effervescence may be exacerbated due to a large number of microcavities in tartrate microcrystals is an additional reason for ensuring the thorough tartrate stabilization of still wine intended for sparkling wine production. Treatment parameters at this stage must take into account the destabilizing... 

In the case of red wines, it is possible to be less demanding, due to the presence of phenols. To simplify matters, Gaillard and Ratsimba (1990) relate the tartrate stability of wines uniquely to saturation temperature. They estimate that stability is achieved if ... 

The presence of peak 2, corresponding to elution of the mannoprotein responsible for tartrate stabilization, confirms that the bond is covalent. Some of the mannoproteins that share covalent bonds with glucane also have a special type of glycosylation, leading to a glycosyl-phosphatidyl-inositol (GPI). The use of a mutant strain (FBYII), deficient in GPI-anchored mannoproteins when cnltnred at 37°C (FBYII-37), showed that the mannoproteins responsible for tartrate stabilization had this type of glycosylation. Two types of mannoprotein extracts were obtained by enzyme hydrolysis of yeast cell walls (FBYII), cultmed at 24°C or 37°C. 

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... 

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. 

When cold treatment is used to clarify new wines or prevent colloidal precipitation, the installation in Figure 12.1 is most appropriate. It may also be used for tartrate stabilization without contact (Section 1.7.2). The process involves ... 

Cation exchangers, which are likely to improve tartrate stability by removing K+ and Ca +, acidify wine by adding H" and, possibly, prevent ferric casse by reducing Fe +. 

Electrodialysis is a method for separating ions using selective membranes that are permeable to ions according to their charges. An electric field moves the ions in one direction or the other. It is thus possible to extract a large proportion of the charged ions from the solution. The principle of electrodialysis is based on the property of selective membranes to allow only cations or anions to pass throngh (Escudier et al, 1998). Initial experiments with electrodialysis were carried out as early as 1975, but it took 20 years to develop a system for tartrate stabilization in wine. 

It has been observed experimentally that varions combinations of cation-permeable and anion-permeable membrane pairs have varying capacities to eliminate different ions. It is possible to enhance potassinm elimination by choosing an appropriate pair of membranes, thus achieving tartrate stabilization without greatly modifying the acetic acid content, as this would be unacceptable. Pairs of membranes that eliminate potassium tend to reduce pH, even if the tartaric acid content is reduced. Membranes selected by Moutounet et al. (1994) reduced pH by under 0.2 units and volatile acidify by just a few percent. 

Membranes used for electrodialysis in tartrate stabilization must meet regulation standards and specific winemaking criteria. Legal requirements for electrodialysis membranes are specified in the Community Code of Oenological Practices and Processes (EC 1622/2000). Membranes must not excessively modify the physico-chemical composition and sensory characteristics of the wine. They must meet the following requirements ... 

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