Ice Crystal Size Changes During Ripening in Freeze Concentration

Abstract

Crystal sizes were measured photographically versus elapsed time for non-uniform ice crystal populations mixed at equilibrium temperatures with sugar solutions. The mass of ice did not change, but crystals smaller than a "neutral diameter," D(n), tended to melt because of their excess surface energy. This subcooled the solution with respect to larger crystals, which consequently grew. This process, "ripening," which slowly increases mean crystal sizes and D(n) is used to produce ice crystals large enough to be cleanly separated from freeze concentrated solutions. "Sequential analysis" was used to determine D(n) and follow changes in the diameters, D(i), of fractions of the ice crystal populations. Rates of change in D(i) for both growth and melting were roughly proportional to (I/D(n) - 1/D(i). Overall mass-transfer coefficients were not markedly different for growth and melting, and decreased from roughly 2 mm/s to roughly 0.5 mm/s as sugar concentration increased 10% to 42%. In 10% sucrose solutions, mass-transfer coefficients decreased from roughly 2 mm/s to roughly 1 mm/s when gelatin was added at levels which increased from 0% to 0.5%. Ripening in freeze concentrated liquid foods apparently can be accelerated by manipulating initial crystal size distributions and temporarily removing high molecular weight components.

Recrystallization in Aqueous Fructose Solutions as Affected by Locust Bean Gum

“…However, they observed that recrystallization rates were dependent on the sugar used and decreased in the order: fructose Ͼ 62DE corn syrup Ͼ sucrose. In a study concerned with recrystallization during freeze drying Smith and Schwartzberg (1985) observed that the presence of low concentrations of gelatin resulted in a decrease in ripening rates. Reid et al (1987) investigated the effects of adding several polysaccharides to aqueous sucrose solutions held at a range of temperatures.…”

A dynamic model of Ostwald ripening in ice suspensions

“…Development of average ice crystal size obtained from model (lines) and experiments (points)[17,19] for solutions of sucrose at different concentrations.…”

Pressure-shift nucleation: A potential tool for freeze concentration of fluid foods

“…This parameter is markedly reduced by relatively small amounts of small particles. Therefore, to obtain clean separations, ice-concentrate slurries should not only have a large average crystal size, but they also should contain as few small crystals as possible (Smith & Schwartzberg, 1985). Moreover, the ice crystals should be convex and not contain pockets or indentations in which the concentrated solution might be trapped.…”