In pasteurisation milk is heated to below boling point, but at a high enough temperature to kill any harmful organisms. The time and temperature is fixed to kill myobacterium tuberculosis. A temperature of seventy one point seven degress for fifteen seconds is used. During this process half of the vitamin c is lost and ten percent of vitamin B one thiamin and B twelve. The protein of the membrane surrounding the milk fat globules is slighlty denatured, allowing fat to rise to the surface to form the cream layer.
In canning the atmosphere inside the can remians asceptic, so food spoilage cannot take place. Canned vegetables and meat are usually heated to one hundred and fifteen degrees.
In modified atmosphere packaging the gas content is changed within the packaging, which slows down the growth of bacteria and microorganisms. Food is sealed in packs that contain oxygen, nitrogen and carbon dioxide. The oxygenretains colour. The nitrogen reduces the rate of oxidation and carbon dioxide stops the growth of bacteria. Examples include bacon and smoked fish. This method extends shelf life for up to seven days more .
In accelerated freeze drying food is quickly frozen and tiny ice crystals are formed, which are rapidly removed by turning to vapour when the food is heated in a vacuum. There is less damage to the food structure and the water content is extremely low. Examples include cofee and mashed potatoes.