ABSTRACT
Although “extraction” often describes the mass transfer process between two liquid phases, in the following the term “extraction” refers to the preferential dissolution of one or more constituents of a solid by contact with a liquid solvent. It is one of the oldest and most commonly used unit operations in the food industry. “Leaching” is another term often used to describe the operation, although originally referring only to percolation of a liquid solvent through a fixed bed of the solid. Sometimes the term “washing” is employed, as it is intimately associated with extraction as a complementary step. The fundamental purpose of extraction is the removal of a soluble fraction from an insoluble, permeable solid phase with which it is associated. The soluble fraction may be solid or liquid, and may be physically held within, chemically bound with, adsorbed on, or mechanically held in the pore structure of the insoluble matrix.
