Food Preservation by Drying. Water is removed from foods:. Under natural field conditions Controlled dehydration processes Common operations such as cooking or baking. Foods dehydration refers to.
aw = p/p0 (0 - 1)
p -water vapor pressure over sample; p0 –water vapor pressure over pure water
%ERH = [p/po ]*100 = [x/x0]*100
x-mole fraction of water vapor over the sample and x 0 -mole fraction of water vapor over pure water
Aged cheddar 0.85
Jams and jellies 0.8
Plum pudding 0.8
Dried fruit 0.6
Milk powder 0.2
0.2-0.3 – monolayer of water –max shelf life for dehydrated
0.35 -0.45 loss of crispness, stickiness, recrystallization of
amorphous state of sugar
0.4-0.5 soft food products like raisins become hard
0.6 critical point above some microbes may grow
0.6-0.8 intermediate moisture food products (chewy granola bars.
Many chemical deterioration reaction reach max rate.
0.85 critical point for microbial spoilage and pathogens growth