3. Conservation of food |

To preserve food is to avoid that microorganisms increase their population which produces changes in the organoleptic properties of food: flavor, smell, colour... There are many different methods to preserve food, but we will study only three of them.

Methods based on cold. If the temperature goes down, microorganisms couldn't reproduce themselves in the same way as they could do at higher temperatures. In refrigeration, temperature must be between 0 ºC and 4 ºC. In freezing, temperature is lower than -18 ºC.
Methods based on heat. When heat is given to food, the largest part of microorganisms is eliminated. In sterilisation, temperature of food is higher than 100 ºC. In pasteurization, the temperature of food is raised until a value between 65 ºC and 75 ºC, during a short time, and after that, the temperature goes down quickly.
Drying food. This is another method to preserve food. Water contained in food is eliminated -by different methods- and microorganisms can't survive without water.

Different methods of drying food

In the next video she explains the diference between dehydrating foods and freeze-dried foods. An example of dehydrating food is raisin (dryed grape), and an example of freeze-dried food is instant coffee. Look at the pictures:


Dehydrating food	Freeze-dried food

It is your turn

Look for information on the internet and write a text explaining how the following preservation methods work: a) salting; b) pickling and c) canning.