Heat and Mass Transfer in Impingement Cooking. Aspects of Food Quality
Hot air impingement is a special form of forced convection, where the air is focused through the use of nozzles at a surface. In combination with rather high air velocities, a jet like phenomenon can evolve, which when used in for example cooking can achieve high heat transfer capacities.
An Impingement oven prototype was constructed. This was used to study some heat and mass transfer situations in meat cooking and bun baking. The aim of the work was to see whether a maximum air temperature of 150°C, could be used while maintaining food quality and cooking times.
The problem was studied by means of statistically planned cooking experiments with three different products; a wet brick (model food), meat (longissimus dorsi from pork) and buns (yeast bread). In addition a method to measure the water content changes in the three products by means of NIR was used.
Cooking in the prototype oven showed that the heat transfer rate was high, which increased the speed of internal heat transfer, thus shortening the cooking time. Meanwhile, this increased the rate of mass transfer to the surface, which slowed the rise of the surface temperature. This meant that when the internal heat treatment was optimal, the surface was still too cold for pronounced browning. Due to this, neither food quality nor cooking time targets are met.
The NIR measurements were successful in that some earlier proposed models were validated to some extent.