Drying

Drying of foods is one of the most common process used for food preservation. Drying is based on the removal of water from a moist material so it decreases the water activity of the material. Therefore drying reduces microbiological activity and minimizes the risk of physical and chemical changes during its storage.


Dehydration operations are important steps in the chemical and food processing industries. The  drying  of  foods  in  order  to  preserve  them is an oldest technique. Most cereals, vegetables, fruits, fish and meat have been preserved by drying from ancient times to nowadays.  Food having high moisture content are very perishable, they can easily undergo some microbial, chemical and physical changes during long time storage. Therefore the reduction of the moisture content to a level which greatly minimizes such risk is main objective of drying. Today conventionally or traditionally dried food consumption is widespread. Snacks, dry mixes and soups, dried fruits and vegetables, etc. are consumed by people. Drying is a difficult food processing operation mainly due to undesirable changes in quality of dried product. During drying, foods undergo physical, structural, chemical, organoleptic and nutritional changes that cause quality degradation.The present demand of high quality products in the food market requires dehydrated foods that maintain at a very high level the nutritional and organoleptical properties of the initial fresh product. A thorough understanding of the factors responsible for the decrease in the quality of the product during the dehydration process is thus of major relevance.Some of the significant features of food dehydration processes, which affect both drying rate and final product characteristics, are considered as: Movement of solubles, Case hardening, Effect upon bulk density, Browning and Shrinkage.  

Hence drying is a combined and simultaneous heat and mass transfer operation for which energy must be supplied. Several types of dryers and drying methods, each better suited for a particular situation, are commercially used to remove moisture from a wide variety of  foods (Somogyi  and  Luh,  1986). Solar drying, Fluidized bed drying, Explosion puffing, Freeze drying, Microwave drying, Hot-air drying are some of the examples of dryers. In order to the interesting concern for meeting quality specifications and energy conservation, emphasize the need for a thorough understanding of the drying process.

Although preservation is the primary reason for drying, it also lowers the product mass and volume . The reduction in mass and volume improves the efficiency of packaging, storing and transportation and reduces the cost. (Goyal, 2006).

 

 


This  text  was prepared  by  Prof. Dr. Fahrettin GögüsUniversity of Gaziantep,  Department  of  Food Engineering, Gaziantep, Turkey.

For further questions please refer to: fahret@gantep.edu.tr