Dehydration is a modern development of smoking and drying, the process is quickened by using a heated oven with a pressure lower than the atmospheric pressure, which prevents the food from spoiling. It is a method of food preservation in which food is dried (dehydrated or desiccated). Drying inhibits the growth of bacteria, yeast and mould through the removal of water. Different kinds of food can be prepared by dehydration. Fruits change characteristics when dried completely.
Plum becomes a prune, the grape a raisin when dries. Figs and dates are also transformed into new, different products that can either be eaten as they are or rehydrated. Home drying of vegetables, fruit and meat can be carried out with electrical dehydrators (household appliance) or by sun-drying. Industrial food dehydration is often accomplished by freeze drying. In this case, food is flash frozen and put into a reduced-pressure system which causes the water to sublimate directly from the solid to the gaseous phase. Although freeze¬drying is more expensive than traditional dehydration techniques, it also mitigates the change in flavour, texture and nutritional value.
Chemical food preservatives are applied to foods as direct additives during processing or they themselves develop it during processes such as fermentation. Certain preservatives have been used for centuries and include sodium chloride (common salt), sugar, acids, alcohols and components of smoke. In addition to preservation, these compounds contribute to the quality and identity of the product and are applied through processing procedures such as salting, curing, fermentation and smoking. Two of the chemicals allowed for preservation are sulphur dioxide and benzoic acid. Both of these substances prevent bacterial activity.
The amount of preservative that can be added to the foodstuff is strictly controlled by law. For domestic use, potassium meta-bisulphate and sodium benzoate are favoured chemicals. These chemicals prevent the growth of micro¬organisms. Pickles, jams, murabbas are preserved by using chemicals like salt, vinegar, sugar, spices etc. Sodium benzoate or potassium meta-bisulphite are used as preservatives for squashes, ketchup etc.