Hot water is recirculate through the pipe and food is metered in
b) Knife peeling
The materials to be peeled (fruits or vegetables) are placed onto a rotating disc and pressed against stationary or rotating blades to remove the skin. Knife peeling is mostly used for citrus fruits, as the citrus skin is easily removed and the fruit suffers little damage.
c) Abrasion peeling
The material to be peeled is fed onto abrasive rollers or fed into a rotating bowl which is lined with an abrasive. The abrasive surface removes the skin, which is then washed away with water. The process is normally carried out at ambient temperature.
d) Caustic peeling
The material to be peeled is passed through a dilute solution (1 to 2%) of sodium hydroxide. This treatment softens the skin, which can then be removed by high-pressure water sprays. A new development in caustic peeling is dry caustic peeling. The material is dipped in a 10 % sodium hydroxide solution. The softened skin is then removed by rubber discs or rollers. A drawback of caustic peeling is that it causes decolourisation of the product.
e) Flame peeling
A flame peeler utilises a conveyer belt to transport and rotate the material through a furnace heated to temperatures above 1000°C. The skin (e.g. paper shell, root hairs) is burned off and then removed by high-pressure water sprays. Flame peeling is used, for example, for peeling onions.