Hypersolubility exponential curve

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...

Once the solubility (A) and hypersolubility (B) exponential curves have been defined, it is possible to determine the state of a wine at a known temperature with considerable accuracy. Indeed, any wine with a KTH concentration, or conductivity, above that defined by the intersection of the vertical line drawn npwards from the temper-atnre of the wine and the exponential solubility curve (A) is in a supersaturated state so, theoretically, there is a probability of spontaneous crystallization. The crystallization phenomenon will, in fact, be observed at the intersection of the same vertical line and the exponential hypersolubility curve (B). It appears, therefore, that supersaturation is necessary, but not sufficient, for primary nucleation phenomena and spontaneous crystallization to occur in a wine. 

The equations for the solubility (A) and hypersolubility (B) curves (Section 1.5.1, Figure 1.11) were established for this purpose by measuring electrical conductivity. They follow an exponential law of the following type C = a e ", where C is the conductivity, t is the temperature and a and b are constants. 

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. 

The envelope covering this set of spontaneous crystallization temperatures (Tcs,) defines the exponential hypersolubility curve (B). The exponential solubility and hypersolubility curves. 

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