Initially, the rate of water loss is high; there is an initial
rapid fall of water content mainly due to loss of surface
water. In vacuum frying this initial vigorous escape of
water is similar to the one obtained under atmospheric conditions,
especially when decreasing the driving force. However,
for longer frying times, a difference between both
technologies is observed. Differences can be partly due to
microstructural changes that might occur during the initial
depressurization step that might affect water escape, after
unbound water surface water is loss. Also, water vapor
accumulation in the head space of the fryer might affect
moisture loss rate, an effect that can be accentuated at
higher thermal driving forces, because of the higher dehydration
rate. In pre-dried vacuum fried apples the loss of
water is even less vigorous because of the lower amount
of water available and because of crust formation during