Cold-stabilized wine

A number of sensory tests have so far revealed no difference in the organoleptic properties of ED- and cold-stabilized wines (Bach et al., 1999 Cameira dos Santos et al., 2000 Goncalves et al., 2003 Paronetto et al., 1977 Riponi et al., 1992 Wucherpfennig and Krueger, 1975). 

Table 1.17. Changes in the physicochemical parameters of cold-stabilized wine when the contact tartrate was recycled (Manjean et al., 1986)...

Fig. 12.1. Schematic diagram of a cold-stabilization installation A, untreated wine (- -14°C) B, treated wine (- -5°C) C, wine during stabilization (—5°C) 1, untreated wine pump 2, treating wine at —5°C (refrigeration system and plate heat exchanger) 3, filter at the end of cold treatment 4, pump for cold-stabilized wine, ready to be filtered 5, heat exchanger for precooling wine to be treated by using it to warm treated wine...

Biologically active particles and fractions may be filtered from fluids using ultrafilters. This process is used extensively by beer and wine manufacturers to provide cold stabilization and sterilization of their products. 

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. 

Commercial wines are commonly tested for protein stability. Wine proteins, upon denaturation by heat or cold, may cause cloudiness and unsightly deposits after bottling. In addition, proteins may combine with iron and copper salts to form flocculate material in bottled wines. The reaction and absorption of proteins on bentonite is an effective means of removing protein from wines (109, 110, 111). Therefore, fining wines... 

Even when no additive is used in winemaking, the necessity for small-lot trial before production scale operation is apparent. Because a high percentage of wine is consumed only after chilling, and because chilling may accelerate the precipitation of potassium acid tartrate, ill-defined colloids, anthocyanin-tannin polymers, proteins, etc., simple cold stabilization by refrigeration in the winery may irreversibly alter the product and its eventually-perceived quality level. It often happens, especially in heavy-bodied red varietal wines, that a dark, amorphous precipitate may form in the bottle over several years. Usually tannoid,... 

The conventional tartaric stabilization techniques applied in the wine industry are based on two opposite principles. One is aimed at heightening HT- and T2- precipitation by reducing wine temperature and leads to the so-called cold stabilization technique. To accelerate nucleation, wines are seeded with exogenous KHT crystals, cooled and kept at —4°C for 4-8 days... 

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. 

Clarification and Stabilization Combinations. Wine clarification may be combined with a stabilization step to minimize handling of the wine. This type of clarification, timing, and sequence vary from winery to winery. Some options used are, after fermentation, rack the wine off yeast lees, bentonite fine for heat stability and chill for cold stability, then diatomaceous earth filter to remove remaining yeast, bentonite, and tartrate crystals after fermentation, centrifuge the wine to remove yeast solids, then chill and add bentonite, and filter to remove yeast and add bentonite, chill, then pad filter to remove bitartrates and protein. 

Stabilization of wines is described by enologists as hot or cold stabilization. Hot stabilization is the term primarily used to describe removal of constituents such as proteins and colloidal materials that may precipitate out of the wine, particularly if the wine is subjected to elevated temperatures such as that used in pasteurizing. Hot stabilization doesn t mean actual use of heat to accomplish this. 

In cold stabilization, cold temperatures are used to cause precipitation of excess potassium acid tartrate out of the wines. If allowed enough storage time at very cold winter temperatures, this precipitation will take place. Under California winter conditions, this reduction of excess tartrates is very slow,... 

Refrigeration. At least one major winery minimizes the amount of wine movement necessary by cold stabilizing the wine at 28° F (-2.22° C) in a jacketed tank until laboratory evaluation shows the wine to be cold stable. The wine is allowed to warm to 30°-32° F (-1. ll°-0° C), then a slurry of bentonite, which has been soaked at least overnight in hot water, is added to the wine at the level prescribed by the previously described laboratory procedure. When the bentonite has settled to the bottom of the tank, the wine is racked off the bentonite lees and filtered to a holding tank. The wine is now ready for polish filtration and bottling. 

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... 

Traditional practices, such as white wine aging on lees in barrels for several months, confer the wine s tartaric salt stability, which dispenses them from any cold stabilization treatment. It has indeed been observed (Moine-Ledoux and Dubour-dieu 2007) that, in the Bordeaux wine-growing area, the majority of dry white wines aged on lees which are not stable in March after their first winter but become stable in June or July without any supplementary cold treatment (Table 5.1). In contrast, wines within the same crus which are not aged on lees systematically undergo cold treatment to obtain stability regarding tartaric salt crystallization. 

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. 

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. 

After fermentation, wine becomes supersaturated with potassium bitartrate. The removal of this excess is necessary to avoid sedimentation after the wine is bottled. A cold stabilization technique where the wine is chilled just above its freezing point is generally used. Protective colloids, which prevent the crystaH ization of the excess potassium bitartrate make a wine resistant to cold stabilization even during prolonged refrigeration. In those... 

It is certainly true that spontaneous crystallization, under natural conditions, is an unreliable, unpredictable phenomenon. This is why the production process for many red and white wines includes artificial cold stabilization before bottling. This type of treatment is justified, especially as consumers will not tolerate the presence of crystals, even if they do not affect quality. 

These theoretical considerations, applied to a short treatment involving seeding with tartrate crystals, show that great care and strict snpervision is required to ensure the effectiveness of artificial cold stabilization. The following factors need to be closely monitored the wine s initial state of snpersaturation, the particle size of the added tartrates, the seeding rate, the effectiveness of agitation at maintaining the crystals in snspension, treatment temperature and, finally, contact time. 

TESTS FOR PREDICTING WINE STABILITY IN RELATION TO CRYSTAL PRECIPITATION AND MONITORING THE EFFECTIVENESS OF ARTIFICIAL COLD STABILIZATION TREATMENT... 

This traditional test is somewhat empirical. A sample (approximately 100 ml) of wine, taken before or after artificial cold stabilization, is stored in a refrigerator for 4-6 days at 0°C and then inspected for crystals. In the case of wines intended for a second fermentation, alcohol may be added to increase the alcohol content by 1.3-1.5% v/v. This simulates the effects of the second fermentation and makes it possible to assess the bitartrate stability of the finished sparkling wine. 

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