Blanching: An Important Unit Operation

Introduction:-

Blanching is an important unit operation in a food processing and done as pretreatment before freezing, canning or drying. This technique is done for the purpose of inactivation of enzymes, modification of texture, removal of trapped air and preservation of color, flavor and nutritional value. Hot water blanching and steam blanching are most commonly used methods in industry but nowadays microwave and hot gas blanching have also been used. Different hot water and steam blanchers are developed to improve its quality efficiency and to improve processing technique with different thermal properties as well as geometries.

Principles and Equipment:-

Studies on effects of blanching as a pretreatment prior to freezing have been reviewed in late in late 1920s and early 1930s. Most vegetables blanched prior to freezing to in activate enzymes that cause developments of off flavors and off colors during freezing. Some exceptions include onions, peppers and leaf because they lose color and flavor during blanching. Gas removal is an important purpose of blanching before canning because it allows easier can fill, reduces strain on can during heating and reduces can corrosion. Fruits are usually not blanched or blanched under mild conditions prior to freezing because blanching produces undesirable texture changes.

Before drying fruits and vegetables are sometimes blanched. After blanching vegetables are quickly chilled by spraying cold water or by conveying them through a flume of cold water. Blowing dry air has also been used to take advantage of evaporative cooling using water adhered to the surface of product.