Blanching is a unit operation prior to freezing, canning, or drying in which fruits or vegetables are heated for the purpose of inactivating enzymes; modifying texture; preserving color, flavor, and nutritional value; and removing trapped air. Hot water and steam are the most commonly used heating media for blanching in industry, but microwave and hot gas blanching have also been studied. Different hot water and steam blanchers have been designed to improve product quality, increase yield, and facilitate processing of products with different thermal properties and geometries. More recently, energy conservation and waste reduction have driven further improvement of equipment design. Although blanching seems a simple operation, heat transfer to a conveyed bed of product and its effects on product properties are very difficult to accurately model with predictive mathematics. Processing conditions are usually set up to inactivate enzymes, but other quality parameters, such as color and texture, are commonly monitored. For a given product, typically mass flow rate is fixed, temperature is measured, and heating media flow rate is adjusted to ensure that the temperature is kept at the set point.
The objective of this article is to review blanching principles and equipment, effects of blanching on product quality, blanching indicators, and energy and waste considerations.
Blanching is a unit operation prior to freezing, canning, or drying in which fruits or vegetables are heated for the purpose of inactivating enzymes; modifying texture; preserving color, flavor, and nutritional value; and removing trapped air. Hot water and steam are the most commonly used heating media for blanching in industry, but microwave and hot gas blanching have also been studied. Different hot water and steam blanchers have been designed to improve product quality, increase yield, and facilitate processing of products with different thermal properties and geometries. More recently, energy conservation and waste reduction have driven further improvement of equipment design. Although blanching seems a simple operation, heat transfer to a conveyed bed of product and its effects on product properties are very difficult to accurately model with predictive mathematics. Processing conditions are usually set up to inactivate enzymes, but other quality parameters, such as color and texture, are commonly monitored. For a given product, typically mass flow rate is fixed, temperature is measured, and heating media flow rate is adjusted to ensure that the temperature is kept at the set point.The objective of this article is to review blanching principles and equipment, effects of blanching on product quality, blanching indicators, and energy and waste considerations.
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