文档介绍：Drying and
Dehydration
Abstract. This chapter reviews basic concepts of drying and dehydration, includ-
ing mass balance analyses. Equilibrium moisture content, water activity, and related
parameters are discussed. Drying methods and drier types are briefly discussed.
Keywords. Dehydration, driers, drying, equilibrium moisture content, evaporation,
water activity.
Introduction
Removing water from food and agricultural products constitutes a significant por-
tion of the processing activity for persons working in the food and agricultural proc-
essing industries. Two major moisture removal methods are drying (or dehydration)
to produce a solid product and evaporation to produce a more concentrated liquid.
The words drying and dehydration are often used interchangeably, especially when
referring to food products; however, only the word drying monly used when
referring to processing of non-food products. Applications range from on-farm drying
of grain, fruits, and vegetables to large mercial drying of fruits, vegetables,
snack food products, milk products, coffee, and other products. Although certain basic
factors are involved in all drying processes, the equipment and techniques vary greatly
depending upon the product and other factors. In this unit, we will consider some basic
factors affecting drying and briefly examine some drying methods.
Evaporation is the removal of some water from a liquid product to produce a more
concentrated liquid. Applications include concentration of milk, fruit juices, and syrup
products. Most evaporation systems are large-mercial operations, although
small-scale farm operations still exist for production of maple, sorghum, and sugar
cane syrups. The governing principles of evaporator operation will be briefly exam-
ined in this unit.
Moisture Content
No agricultural product in its natural state pletely dry. Some water is always
present. This moisture