Blanching exposes food products to boiling water or steam for a brief period of time and then quickly cools them to halt the cooking process. Blanching is one of the most important operations in the processing of foods. It is used to remove sugars or starches from a product or to provide heat treatment to a product to facilitate product handling.

Blanching removes trapped air and metabolic gases within vegetable cells and replaces them with water. It is also used for the removing of skins in fruit and vegetable processing. Blanching a product is done by a food processing machine called a blancher.

Benefits:

• Preserves flavor and texture
• Cleanses the surface
• Brightens color
• Retard loss of vitamins
• Softens vegetables

Most blanchers employ belt, rotary drum or screw technology to move the product through the processing machine. The heating can be done by hot water, steam or other liquids in a continuous or batch manner. A blancher immerses the product in the hot water or steam and maintains it at a constant temperature. The product remains immersed in the steam or hot water for a specified amount of time.

Types of Blanchers

In steam blanchers, a product is transported by a chain or belt conveyor through a chamber where steam flows through at approximately 100°C. Steam blanching is usually used for cut and small products, and requires less time than water blanching because the heat transfer coefficient of condensing steam is greater than that of hot water.

Steam blanchers retain solids and nutrients and tend to yield a crispier, fresher looking product. They also leave less excess water on the product, which makes them desirable for freezing operations.

A water blancher consists of a pan with inlet and outlet ends. In the bottom of the pan are a number of outlets that are connected to a circulation system. The circulation system distributes the water back to the pan through injectors. The water is heated by directly injected steam or by a heat exchanger.

A hood, above the full length of the pan, is equipped with a paddle conveyor. The paddles go down into the pan and divide the blancher into suitable compartments, ensuring the set blanching time to the product. Water blanching is performed typically from 70°C to 100°C. Water blanching usually results in a more uniform treatment, allowing processing at lower temperatures.

Specifications

Specifications for blanchers include the following:

• Capacity (kg/h)
• Steam Consumption (kg/h)
• Blanching Temperature (?)
• Processing Duration (minutes)

Blanchers are very similar to cookers and pasteurizers. The basic difference between a blancher, cooker or pasteurizer are retention times and operating temperatures. Blanchers normally operate for a short time and at higher temperatures. Cookers typically are operated with longer retention times and higher temperatures. Pasteurizers operate at lower temperatures and longer retention times.

Image credit:

LYCO Manufacturing