Blanching is a cooking process for vegetables, fruits and other foods. The food is exposed to steam, hot air and/or boiling water or hot oil for a short period of time after which is quickly cooled with water or air to stop the cooking. Blanching inactivates enzymes that cause discoloration to enhance flavor and color and otherwise improve quality and/or prevent degradation. Blanching with liquid will also wash the food removing pesticide, dirt and other residues.

Rotary blanchers are used in food processing plants to blanch high volumes of foods in a continuous process. Rotary blanchers consist of a screened horizontal cylinder in an outer, enclosing, tank. A helix or screw runs through the center of the cylinder.

For liquid blanching the cylinder is partially submerged in water. Spray jets for more vigorous washing may also be used. For steam or hot air blanching, jets inside and outside the cylinder do the cooking or blanching. This cooking section takes up the first portion of the cylinder.

Food is introduced into a chute at the center of the cylinder infeed end. As the cylinder rotates, the helix gently carries the food along its length. In the cooking section it is heated to the desired temperature. The length of the section, the temperature of the heating medium and the rotational speed of the cylinder determine the cooking parameters including time. In the second section of the cylinder, the food is exposed to cool or chilled water or air and cooled to the desired temperature.

At the end of the cylinder the food is discharged to a chute or conveyor to be carried to the next production process.

Steam or hot air blanching has the advantage of reduced energy consumption when compared to hot water. A disadvantage is that it does not wash the food and residues will not be removed. Not washing the food may, in many cases be an advantage since washing can remove flavors, vitamins and nurtients.

Rotary blanchers may have internal clean-in-place (CIP) systems and even steam-in-place systems to automate cleaning and sanitation. This is a highly desirable feature as it can save considerable downtime and labor between products.