Abstract: Using the method to divide the whole yoghourt drying process into some parts, the operation parameters under maximal sublimation rate were studied in this paper. To aim at the sublimation rate reaching to maximum, the calculation models for maximal sample thickness and sublimation time in frozen layer temperature Ti were derived from the sublimation rate formula for pure ice on the assumption that the frozen layer temperature Ti rise from terminal frozen temperature Tf to melting temperature To in concentrated yoghourt freeze-drying process. The calculation models for shelf temperature Tis at Ti were derived from massand heat balance principles. Taking Tis according with drying time as shelf temperature to control freeze-drying process the water content of products reached to 0.3%～0.5% when forecast time were prolonged 10% which was 21.5, 10.2 and 5.2h respectively while terminal frozen temperature Tf was at -30, -28 and -26℃ and thickness was 19, 13 and 8mm respectively. The products accord with freeze-drying food standard.

Key words: freeze-drying, maximal sublimation rate, thickness, temperature, pressure