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How the drying curve looks like

The drying curve varies according to the type of food and the kind of drier that is used, and also the way the food material also responds to temperature, humidity, air velocity and direction of air and thickness of food. Oil-in-water emulsion dries only quickly than water -in-oil emulsion. 

Case hardening is common with foods that contain dissolved sugars and other solutes in high temperature. As water leaves cells of the food, solutes are retained by cell membranes and air spaces in surface layers can act by capillary action whereby water caries solutes to the surface during drying and leaves them there. In some fruits, this can cause sticky sugary exudates on the surface, which shrinks and clogs pores leading to case hardening.



Excerpts from the book, Basic principles of food  processing and preservation: Easy notes by Ukponmwan, Ifueko. Get it from the online store www.morebooks.de 


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