Thursday, January 28, 2016

Ice crystal formation

Freezing is the crystallisation of water, and the freezing point is the temperature at which ice crystals can be sustained in equilibrium with water. The freezing point of water is depressed by the addition of solute.

Unlike pure water ice crystal formation and growth in aqueous solutions occurs over a temperature range. The process begins with a decrease of the temperature below the freezing point of the solution. Once it has arrived at this point, the nucleation or formation of the ice glass nuclei begins. The nuclei are formed for a mechanism of homoemous nucleation or molecular addition.

Once ice crystal nuclei have been formed, the following step is crystal growth. In the stage of crystal growth, different process can be present that include the diffusion of water molecules from the bulk solution toward the ice crystal surface, with subsequent incorporation of these molecules into the crystalline reticule that also include the transfer of of the formation of latent heat from the crystal surface toward the bulk solution.

As ice forms during cooling, only water molecules comprise the ice crystals. As a result, all other components (salts, etc) become concentrated in the remaining solution. As the solution concentration increases, the chemical potential of the water in the solution decreases.

Water will continue to crystallise until the chemical potential of the water in the liquid phase equals the chemical potential of the water in the solid phase. In other words, the remaining solons will reach it equilibrium freezing point.

In meat processing, ice crystals may shorten shelf life by puncturing membranes and causing fluid loss from muscles. They also lower metmyoglobin reducing power, and induce off-colour development and inferior bloom.
Ice crystal formation

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