The Continuous Wok — A New Unit Operation in Industrial Food Processes

Abstract

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.

Reprocessing effect on the quality of domestically cooked (boiled/stir-fried) frozen vegetables

“…In this last study, the loss of sample moisture would account for the increase in the firmness ratios, especially in steaming+hot air treatments, resulting in a potato that is firmer but whose texture is unacceptable to the consumer. On the other hand, stirfrying of vegetables and meat entails a short cooking time and high rates of heat and mass transfer [21]. The degree of cooking depends on the internal temperature reached at the thermal centre of the product, the heating method and the heating rate attained in the treatment [22].…”

Temporal reflectance changes in vegetables

“…Celeriac and carrots were the subjects of this study, where we measured the reflectance properties using a multispectral imaging device called VideometerLab which will be described in the next section. The pre-fried vegetables were produced by a new process for continuous stir-frying in industrial scale, which has been introduced for producing convenience high-quality vegetables [1]. The pre-fried vegetables have a low fat content (typically 1%-2% of the product weight), a texture and flavor similar to what can be achieved in the kitchen, and vitamins are preserved almost 100% [5].…”

Multispectral Imaging of Wok-Fried Vegetables

“…Celeriac and carrots (shaped as cubes of size approximately 0.5 cm3) were fried in a continously wok (Adler-Nissen, 2002). Afterwards the products were packed in plastic bags and frozen at -30°C.…”

“…Freeze-chiling allows the manufacturer flexibility in manufacturing and distribution. The pre-fried vegetables are produced by a new process for continuous stir-frying in industrial scale, which has been introduced for producing convenience high-quality vegetables (Adler-Nissen, 2002). The pre-fried vegetables produced according to the process are generally prepared from the raw.…”