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HNSC 1200 (46)
Snehil Dua (46)
Chapter 2

HNSC 1200 Chapter 2: Topic 2.6
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Department
Human Nutritional Sciences
Course
HNSC 1200
Professor
Snehil Dua
Semester
Winter

Description
o982 Physical: 4 types- drying, thermal processing, cooling and irradiation 1. DRYING: involves removal of water from foods oldest form of food preservation the food is preserved b/c microorganisms cannot survive in a dry environment. Bacteria and mold need approx. 15% moisture level to survive, yeast needs approx. 20% foods can be eaten dry or can be rehydrated - Drying techniques: in ancient times drying was done predominantly by the sun. The sun provided the heat to encourage evaporation of water from foods. the hotter the environment, the faster the food dries. Not typically used now b/c is a slow process, and food is exposed to weather and potentially insects currently the food insdustry uses commercial drying processes such as oven/plate drying, spray drying, drum drying and freeze-drying oven / plate drying: food spread on slatted floor or on shelves inside kilns or drying rooms. hot air is then blown over and through the food. Alternatively, food can be placed on trays that travel through a tunnel of hot air. E.g: slices of fruits are placed on conveyer belts that are hot. the high temperature removes the moisture from the food and often the moisture is removed by creating a vacuum environment. This speeds up the loss of moisture from the fruit. see figure 16.8 in textbook. spray drying: used main;y for liquid products (e.g. milk, eggs, instant coffee). A hot chamber equipped with a vacuum and a spray nozzle is required. The spray nozzle sprays very tiny droplets of the milk into the chamber and the high temperature of the chamber immediately dries these droplets. By the time the droplets get to the bottom of the chamber, they are dried and are collected. The vacuum ensures constant removal of the moisture from the chamber to speed up the drying process. Since the particle size of the powder is very small, milk powder prepared by this method has many better solubility. drum drying: used for foods like mashed potato flakes and quick cooking hot cereals. The product is first ev
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