Food preservation

Food preservation is about the ways and means which help to preserve food. Food spoils from bacteria if it is not treated.  For thousands of years, humans have used methods of preserving food, so that they can store food to eat later. The simplest methods of preserving food, such as drying strips of fish or meat in the hot sun have been used for thousands of years, and they are still used today by indigenous peoples. The other ancient method is to use salt, and often drying and salting are done together. 

Food spoils mainly by decomposition by microorganisms. There are five basic techniques which make food last longer:
 Killing the microorganisms, or preventing them from multiplying
 Contact of microoganisms with food is prevented
 Certain additives prevent or slow the growth of microoganisms; this is often called curing
Usually several of the techniques are combined.

Methods of preserving food
Common ways of preserving food are:

Heating the food or baking it (a hard corn-flour biscuit stays edible much longer than a bowl of fresh corn)
Pasteurization: Louis Pasteur found that simply heating food kills most microorganisms and makes it last longer. Liquids such as milk are commonly pasteurized. However, the heating has to be done precisely according to a procedure
Converting the food into a longer-lasting form (for example, fresh goat's milk can be converted into cheese or yogurt, which lasts much longer than fresh milk)
Pickling: putting vegetables, meat, or fish in salty water (brine). Salting the food:  Covering it with dry salt
Putting the food in a jar with alcohol (ethanol) or vinegar, also called pickling
Putting large amounts of sugar into the food (for example, as with jam or fruit jarred in sugar and water)
Drying in the sun or in an oven
Smoking the food with the smoke from burning wood. Usually, this is done to food that was salted first.
Keeping the food cold or frozen, including freeze-drying
Adding other preservatives such as sorbates (sorbic acid), sulfites and nitrites.

Multiple methods
Many common methods use several of these approaches at the same time. For example, pickles preserved in a jar are heated then put in a mixture of vinegar and brine. Fruit jams and jellies are heated and mixed with a large amount of sugar. Some preserved fruit is heated and then mixed with alcohol (for example, Brandy) and a large amount of sugar. Smoked hams are cured in brine and then exposed to the smoke from burning wood chips.