Immersion chilling and freezing: a promising process for chilling, freezing and-or formulating

Direct contact chilling and freezing in a concentrated aqueous solution consists in soaking foodstuffs into a chilled aqueous solution (<5°C). Binary brine solutions (sodium chloride, calcium chloride) are generally used, less frequently ternary or more complex solutions (water+salt+ethanol or water+sugars). Compared to air blast freezing process, immersion freezing allows much quicker freezing times, with subsequent potential energy savings. Neverless, this freezing methodology is still empirical and its full development was hindered by uncontrolled penetration of solutes into the food material. Preliminary experiments on model foods gelatin gels dipped into binary sodium chloride solutions, were carried out to study simultaneous heat and mass transfer. The evolution of water loss, solute gain, core temperature and phase change as a function of time was assessed. Results showed that it was possible to control solute impregnation through process variables : temperature/concentration of the AF, agitation, time... Particularly, the quick formation of a boundary ice barrier, inside the food material, would limit the subsequent mass transfer. Various applications of these results to foodstuffs, freezing of pieces of apples, and onboard chilling of sardines, are also presented.