Steam Blanching

• Steam blanching


  Transferring the kinetic energy from the hot water vapor into the molecules of the food
• Steaming vs boiling/blanching


  The food is in direct contact with the water before the molecular bonds are broken instead of afterwards
• Steaming


  1. Boiling water continuously, causing it to vaporize into steam

  2. The steam then carries heat to the nearby food, thus cooking the food
• Steaming


  The food is kept separate from the boiling water but has direct contact with the steam, resulting in a moist texture to the food
• Steam blanching


  • Preferred method for foods with a large area of cut surfaces as leaching losses are much smaller than those found using hot-water blanchers
• Conventional steam blanching


  1. A mesh conveyor belt carries food through a steam atmosphere in a tunnel

  2. The residence time of the food is controlled by the speed of the conveyor and the length of the tunnel

  3. Typically, a tunnel is 15m long and 1–1.5m wide
• Conventional steam blanching


  • Often poor uniformity of heating in the multiple layers of food
  • The time–temperature combination required to ensure enzyme inactivation at the centre of the bed results in overheating of food at the edges and a consequent loss of texture and other sensory characteristics
• Conventional blanching methods are mastered and well adapted to the industries nowadays, but they are not sustainable due to the high water wastes and energy consumption
• Non-conventional blanching methods


  • Microwave blanching
  • Infrared blanching
• Conventional blanching methods


  • Conventional-water
  • HTST
  • LTLT-steam
• Non-conventional blanching methods


  • Microwave-HTST
  • Microwave-HTSTLTLT
  • Infrared
• Conventional steam blanchers


  • Smaller loss of water-soluble components
  • Smaller volumes of waste and lower disposal charges than water blanchers, particularly with air cooling instead of water
  • Easy to clean and sterilise
• Conventional steam blanchers


  • Limited cleaning of the food so washers also required
  • Uneven blanching if the food is piled too high on the conveyor
  • Some loss of mass in the food
• Conventional hot-water blancher


  • Lower capital cost and better energy efficiency than steam blanchers
• Conventional hot-water blancher


  • Higher costs in purchase of water and charges for treatment of large volumes of dilute effluent
  • Risk of contamination by thermophilic bacteria