Drying: Drying removes the moisture from the food so that bacteria, yeasts and moulds can’t grow and spoil the food. It also slows down the action of enzymes but doesn’t inactivate them. When the food is ready for use, the water is added back and the food returns to its original shape. Foods can be dried in the sun, in an oven or in a food dehydrator by using the right combination of warm temperatures, low humidity and air current. The optimum temperature for drying food is 140 °F. If higher temperatures are used, the food will cook instead of drying. When the food cooks on the outside and the moisture can’t escape, "case hardening" can occur. The food will eventually mould. To dry food, the water must move from the food to the surrounding air. If the surrounding air is humid, then drying will be slowed down. Increasing the air current speeds up drying by moving the surrounding moist air away from the food. To speed the drying time, increase the airflow. Foods, which are dried, include fruit, seeds, nuts and vegetables.
Vacuum packed/Sealed container: Canning is the process in which foods are placed in jars or cans and heated to a temperature that destroys micro organisms and inactivates enzymes. This heating and then cooling forms a vacuum seal. The vacuum seal prevents other microorganisms from recontaminating the food within the jar or can. Acidic foods like fruits and tomatoes can be processed or canned in boiling water, while less acidic foods like vegetables and meats are processed in a pressure canner at 240 °F (10 pounds pressure at sea level).
Preservatives: Preservatives are used for foods, which aren’t frozen or dried. They are needed because there is always lag time between harvesting and packaging. Chemical preservatives include Sodium nitrate and Sulphur dioxide. Sodium nitrate cures meat and prevents bacteria growth which otherwise would cause severe food poisoning. Sulphur dioxide is added to jams, beer, fruit juices and wine it stops the growth of bacteria and fungi. Radiation is used after the product is sealed in plastic wrapping. It receives a small dose of gamma rays, which kill any bacteria of parasites in the food. As it is only a small dose the food doesn’t become radioactive.
Pasteurisation: Pasteurisation is a compromise. If you boil a food you can kill all bacteria and make the food sterile, but you often considerably affect the taste and nutritional value of the food. When you pasteurise a food, normally a liquid, you are basically heating it to a high enough temperature to kill certain bacteria and to inactivate certain enzymes, and in return you are lowering the effects on taste as much as you can. Commonly pasteurised foods include milk, ice cream, fruit juices, beer and non-carbonated beverages.
Smoking: Smoke cooking is done at higher temperatures in order to cook the meat. Smoke curing is just smoking cured meat or sausage. Although smoking meat does provide some preservative effect, by itself it isn’t sufficient to allow long-term storage. Smoke is a very complex material, with more than 200 components that include alcohols, acids, phenolic compounds, and various toxic, sometimes carcinogenic substances. The toxic substances slow down the growth of microbes and the phenolics slow down fat oxidation. Foods such as meat and fish, especially salmon, are smoked not just because of preservation but also because of taste.
