The continuous wok - a new unit operation in industrial food processes

The preparation of fine cut vegetables and meat by stir frying is characterized by a short cooking time and high rates of heat and mass transfer, which makes scale-up difficult. A new principle for carrying out an industrial, continuous stir frying process is studied at pilot plant scale. The ingredients are transported in a horizontal, open frying tube by a conveyor helix while being tossed by scrapers and stirring rods mounted on the helix. During the frying process the average product temperature stabilizes around 80C despite the intense heating, and this may explain why the texture of stir fried vegetables is firmer than the texture of vegetables cooked in water. However, the heat inactivation of a model microorganism applied as a surface contaminant showed that the effective surface temperature was above 90C which ensures a safe process. Vigorous evaporation from the free surfaces of the turning pieces may cause this temperature gradient to be established by an evaporation cooling effect.