Over the centuries, the techniques and principles of food storage and preservation have greatly evolved: drying, smoking, canning, pasteurization, refrigeration, freezing, vacuum packing, etc. However, the goal remained the same: to protect food from the spread of micro-organisms (bacteria, fungi, enzymes) that are the main factors of its spoilage.
Few foods are shelf stable without a minimum of care. Apples, potatoes and carrots are an exception. You can keep apples for several weeks in the dark in a well ventilated area. Potatoes and carrots can be stored for several weeks in the dark or buried in sand. However, for other foods, you will need to make use of various storage methods in order to preserve the flavor as well as the vitamins.
This technique is widely used for preserving fruits, some vegetables and herbs and more rarely, meat and fish. Its purpose is to force the food loose a part of its water content in order to prevent the spread of microorganisms. Among the most common foods that can be stored by means of the drying technique are apricots, figs, plums, but also hazelnuts and walnuts.
The traditional drying technique has been greatly improved by the technique of freeze drying, aimed at separating the food of its water. Instead of using the natural heat and the evaporation process, it lies on a sudden freezing (-40 ° C and -80 ° C) associated with a transition from solid to gaseous state of the water in vacuum. Freeze-dried foods are stored in closed containers away from moisture. This technique is mainly used for instant coffee, powdered milk, soups and some elaborate preparations.
Food refrigeration is by far the most often used storing food technique nowadays. However, it can be applied solely for a few days. By keeping food away from heat, the growth of microorganisms is slowed down, but not stopped. This food storing technique can be efficient only if the refrigerator works at a temperature between 4 and 8 ° C. It can be used to keep meat, fish, vegetables and dairy products in good condition for 4 to 10 days, depending on the food. Packaging is important in a refrigerator because the cold temperature dries foods out.
A widely used technique nowadays that we benefit from advanced storing food technology, freezing is aimed at optimally preserving food for longer periods at temperatures below 0 ° C. The spread of microorganism is stopped and the products keep a texture almost identical to fresh produce.
Aimed at killing bacteria, heat preservation takes two forms:
a) Pasteurization involves subjecting such foods to a temperature between 65 and 100 ° C and cooling them brutally. It is regularly used for preserving milk, cheese, butter and other dairy products.
b) Sterilization (also called canning) goes further than pasteurization. Food is brought to a high temperature (between 115 and 121 ° C) for several minutes in sealed cans or jars. Under the influence of heat, the water present in containers is converted into steam which can expel the air. It is used with fruit, vegetables or cooked preparations which can be then stored at room temperature for several months.
Besides these main techniques, there are others based on a chemical reaction. Fruit can be well preserved in alcohol, meat and fish can be kept in salt but also by smoking, vegetables can be stored in acidic medium such as pickles or in a basic medium such as tomatoes and cheese in oil. Sugar is also a powerful conservative since it prevents bacteria from developing. There are also modern food storing techniques like ionization (removal of living cells by irradiation), and vacuum packaging, but they are less wide spread within households.