Potassium bitartrate crystals

To prevent the formation of wine crystals during the bottling process, winemakers use a method known as cold stabilization. By lowering the temperature of the wine to 19-23°F for several days or weeks, the solubility of tartrate crystals is lowered, forcing the crystals to sediment. The resulting wine is then filtered off the tartrate deposit. The temperature dependence of the solubility of potassium bitartrate is readily apparent in the following comparison while 162 ml of water at room temperature dissolves 1 g of the salt, only 16 ml of water at 100°C are needed to solubilize the same amount of saltJ l Recent developments employ a technique known as electrodialysis to remove tartrate, bitartrate, and potassium ions from newly fermented wine at the winery before potassium bitartrate crystals form. 

The method most commonly used to stabilize a wine, once instability is determined, is to chill the wine to -5° C and hold it until stability is achieved, usually seven to fourteen days. Addition of fine potassium bitartrate crystals during chilling (30 mg/L) helps seed the formation of potassium bitartrate crystals. When laboratory tests have shown the wine to be stable, the wine goes through a tight diatomaceous earth or pad filtration to remove the crystals. 

Care must be taken when fining a sparkling wine with bentonite in order to preserve its foaming properties. Excessive use of bentonite for the fining of sparkling wine cuv es can produce a finished product that has a large bubble size and a poor bubble stability as a result of a reduction in both protein and peptide contents. Cold stabilization procedures cause both a precipitation of potassium bitartrate crystals as well as proteins because of the downward shift in pH. This precipitation of proteins... 

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)...

In other work, Moine-Ledoux et al. (1997) reported that the use of Mannostab at doses ranging from 15g/hL to 25g/hL inhibit potassium bitartrate precipitation (Table 5.2) while excess amounts of this additive, that is 30g/hL, are ineffective on potassium bitartrate crystallization (Table 5.2). Within the extracts, compounds responsible for the stabilizing effect observed were found to be highly glycosylated mannoproteins of molecular masses ranging from 30 kDa to 40 kDa possessing a glycosyl-phosphadityl-inositol anchor (GPI) (Moine-Ledoux and Dubourdieu 1999, 2002,2007). 

It is normal to find potassium bitartrate crystals, associated with precipitated condensed coloring matter, in wine with several years aging potential. When phenols condense, they become bulky, precipitate and are no longer able to express their protective colloid effect. 

However, metatartaric acid is hydrolyzed in wine, and loses its effectiveness, while adding tartaric acid may even facilitate potassium bitartrate crystallization. Under the same conditions, manno-proteins 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). 

For the production of tartar emetic (antimony potassium tartrate [28300-74-5]), potassium bitartrate [868-14 ] and antimony oxide, Sb202, are added simultaneously to water in a stainless-steel reactor. The reaction mixture is diluted, filtered, and collected in jacketed granulators where crystallization takes place after cooling. Centrihiging, washing, and drying complete the process. 

The brine solution may be enriched with NaCl or KHT to increase its conductivity and acidified to the same pH of the wine under treatment. It is recirculated between the concentrating compartments of the ED stack and another tank equipped with conductivity and pH automatic controls so as to avoid precipitation of potassium bitartrate onto the membranes by diluting the brine with deionized water and/or discharging more or less aliquots of the brine itself when its conductivity reaches 70-80% of its saturation value (Goncalves et al., 2003). In this way, a waste effluent in the range 10-20% of the wine volume treated is to be disposed of or used to recover KHT crystals (Nasr-Allah and Audinos, 1994). 

Tartrate, corresponding base of tartaric acid. The mixed potassium-sodium-salt is the famous tartrate (potassium bitartrate), which crystallizes on the cork of wine bottles (Seignette salt). 

Unfavorable bottled wine storage conditions may cause the appearance of haze or deposits in white wines. Excessive heating of a bottle of white wine may precipitate protein, causing a haze or cloud excess cold may crystallize potassium bitartrate, creating a layer of small crystals in the bottle. Such haze and precipitates in wines may or may not have negative sensory effects but often affect adversely consumer reaction to the wine. 

Bitartrate Stabilization. Potassium and tartaric acid are natural constituents of the grape. Wine content of these constituents depends on a number of variables, not all well understood variety, vintage, and weather pattern degree of skin contact alcohol level bitartrate holding capacity of phenolic compounds and potassium binding capacity of the wine (30, 35). Most wines after fermentation are supersaturated solutions of potassium bitartrate. This compound is less soluble at lower temperatures, and, thus, lower temperatures will cause precipitation of bitartrate crystals. This lowering of temperature and subsequent removal of crystals by filtration is called cold stabilization. 

Derivation By heating antimony trioxide with a solution of potassium bitartrate and subsequent crystallization. 

Part of the original fruit acids may be consumed by yeasts and, especially, bacteria (see malolactic fermentation ). On the other hand, yeasts and bacteria produce acids, e.g. succinic and lactic acids. Furthermore, acid salts become less soluble as a result of the increase in alcohol content. This is the case, in particular, of the monopotassium form of tartaric acid, which causes a decrease in total acidity on crystallization, as potassium bitartrate still has a carboxylic acid function. 

An increase in true acidity, i.e. a decrease in pH, may occur during bitartrate stabilization, in spite of the decrease in total acidity caused by this process. This may also occur when must and, in particular, wine is tartrated, due to the crystallization of potassium bitartrate, which becomes less soluble in the presence of alcohol. 

Fig. 1.11. Determining the solubility (A) and hypersolubility (B) exponential curves of potassium bitartrate in a wine. Defining the hyper-saturation and instability fields according to the KTH content (Maujean et al, 1985). DS = saturation field 1, dissolved KTH 2, supersaturated, surfused KTH 3, crystallized KTH rcs , spontaneous crystallization temperature when 1.1 g/1 KTH is added rsat , saturation temperature of a wine in which 1.1 g/1 KTH have been dissolved...

The exponential hypersolubility curve (B) is obtained experimentally and geometrically from the envelope linking the spontaneous crystallization temperature (TCS, ) points of a wine brought to various states of supersaturation by completely dissolving added KTH and then reducing the temperature of the wine until crystallization is observed. The exponential hypersolubility curve represents the boundary between state 2, where potassium bitartrate is in a state of supersaturation (C — S) and surfusion, and state 3, where it is crystallized. 

It has been experimentally verified (Maujean et al., 1986) that the crystallization rate, monitored by measnring the electrical conductivity of wine, is directly proportional to the surface area of the liquid/solid interface represented by the nuclei. This result is consistent with the following eqnation, proposed by Dunsford and Boulton (1981), defining the mass velocity at which the precrystalline aggregates of potassium bitartrate diffuse towards the surface (A) of the adsorption interface ... 

Fig. 1.16. Crystallization kinetics of potassium bitartrate analyzed by measuring the drop in conductivity of a wine according to the type of treatment or fining. Samples were stored at 2°C, seeded with 5 g/1 of KTH and subjected to the static contact process for four hours (Maujean et ah, 1986)...

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. 

Crystalline Crystal-like Fibrous Amorphous Potassium bitartrate, calcium tartrate, or calcium oxalate Cork fragments or diatomaceous earth Cellulose, case lint, or asbestos Protein, phenolic, polysaccharide (glucan, pectin, or starch) or metallic casse... 

L-Tartaric acid is found in wines as the poorly soluble potassium hydrogen tartrate salt (potassium bitartrate) that often crystallises in young wines and when the wine is cooled as cream of tartar, known in winemakers jargon as tartrates. The crystals are harmless, but their presence is generally undesirable to consumers. The cream of tartar formation can be prevented by cold stabilisation of wines. 

The fact that molecules have a three-dimensional structure and shape was shown by Louis Pasteur in 1848 in some critical experiments on crystalline salts of tartaric acid that formed part of his doctoral studies. Tartaric acid is a naturally occurring compound that is extracted from grape juice and sometimes crystallizes as potassium bitartrate from solution in wine. Pasteur concentrated on the related compound sodium ammonium tartrate. The two forms of tartrate were chemically identical, but a solution of potassium bitartrate would rotate the plane of polarization of plane polarized light to the right whereas a solution of sodium ammonium tartrate would not. Pasteur studied the crystal structures of tartaric acid salts and found the crystallites themselves were chiral, i.e. the facets of the crystals occur in two forms that are mirror images of one another, so that the two crystallite forms cannot be superimposed. In the pure potassium bitartrate, only right-handed facets were... 

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