During freezing, the food surface has a higher temperature than the circulating air, and, thus, the surface water vapour pressure, Pva, is also higher than that of air. The lower the freezing speed, the slower the decrease in surface temperature, and this results in greater differences of vapour pressure between food and air. In addition, the duration of the freezing process will be longer, both factors increasing the weight loss. The higher the cooling speed, the lesser the sublimation.