Influence of heating and keeping warm on the quality of meals.

Meals produced on a large scale for public feeding establishments (sterilized, quick frozen, cooled) have to be heated before they are served. Meals prepared in central kitchens are kept warm for several hours. The influence of heating and holding is explained with quick frozen meals being kept warm as examples. If quick frozen meals in multi-portion trays are heated (hot-air oven) under unfavourable conditions and up to high central temperatures, the content of the various vitamins is notably reduced. Vegetable meals also show an inferior sensorical quality. The meals should be kept warm in a way that, on the one hand, microbiological risks are avoided and that, on the other, quality changes are minimized. The higher the holding temperature, the more thermolabile ingredients are destructed. During a holding time up to 5 hours at temperatures ranging from 60 degrees C to 80 degrees C, losses to varying degrees of vitamins C, B1, B2, niacin, retinol and beta-carotin occurred in nearly all meals. A holding time of max. 3 hours seems possible if a certain detraction from the nutrition-physiological and sensorical quality is tolerated.