Bitartrate instability

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. 

There are two main types of must and wine treatment technologies for preventing bitartrate instability based on the phenomenon of low-temperature crystallization. The first uses traditional slow stabilization technology (Section... 

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. 

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. 

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 temperatnre at which a wine becomes capable of dissolving bitartrate is a nseful indication of its state of supersatnration. However, in practice, enologists prefer to know the temperature below which there is a risk of tartrate instability. Maujean et al. (1985, 1986) tried to determine the relationship between saturation temperature and stability temperature. 

A volume of wine is pumped into the treatment vat and then into the diluate circuit of the electrodialysis cells. When conductivity reaches the set point, determined by an instability test, the wine is automatically pumped into a reception vat using a system controlled by solenoid valves. A new volume of wine is then pumped into the system and stabilized under the same conditions. Treatment time and, consequently, the performance of the system depend on the wine s degree of instability. Treatment flow rates vary from 50 to 150 1/h/m, depending on this parameter. The concentrate circuit consists of a saline solution that collects the ions extracted from the wine. The ion load is adjusted by adding water to avoid the precipitation of bitartrate crystals inside the small, easily blocked cells. This function is also automatically controlled by conductivity measurements. 

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