Food preservation usually involves preventing the growth of bacteria, fungi (such as yeasts), and other micro-organisms (although some methods work by introducing benign bacteria or fungi to the food), as well as retarding the oxidation of fats that cause rancidity. Food preservation can also include processes that inhibit visual deterioration, such as the enzymatic browning reaction in apples after they are cut, which can occur during food preparation.
Many processes designed to preserve food will involve a number of food preservation methods. Preserving fruit by turning it into jam, for example, involves boiling (to reduce the fruit’s moisture content and to kill bacteria, yeasts, etc.), sugaring (to prevent their re-growth) and sealing within an airtight jar (to prevent recontamination). There are many traditional methods of preserving food that limit the energy inputs and reduce carbon footprint.
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is ingested by an organism and assimilated by the organism's cells in an effort to produce energy, maintain life, or stimulate growth.
Historically, people secured food through two methods: hunting and gathering, and agriculture. Today, most of the food energy consumed by the world population is supplied by the food industry.
Canning is a method of preserving food in which the food contents are processed and sealed in an airtight container. Canning provides a shelf life typically ranging from one to five years, although under specific circumstances a freeze-dried canned product, such as canned dried lentils, could last as long as 30 years in an edible state.
In 1795 the French military offered a cash prize of 12,000 francs for a new method to preserve food. Nicolas Appert suggested canning, and the process was first proven in 1806 in tests conducted by the French navy. Appert was awarded the prize in 1810 by Count Montelivert, a French minister of the interior. The packaging prevents microorganisms from entering and proliferating inside.
A Mason jar is a molded glass jar used in canning to preserve food. The mouth of the jar has screw threads on its outer perimeter to accept a metal ring (or "band"). The band, when screwed down, presses a separate stamped steel disc-shaped lid against the rim of the jar. An integral rubber ring on the underside of the lid creates a hermetic seal to the jar. The bands and lids usually come with new jars, and bands and lids are also sold separately; while the bands are reusable, the lids are intended for single use when canning.
While largely supplanted by other methods, such as the tin can and plastic containers, for commercial mass production, they are still commonly used in home canning.