Various techniques for preserving food use:
- physical processes, such as refrigeration and cooking
- biological processes, such as fermentation.
Which preservation techniques alter the temperature of food?
Refrigeration and freezing use low temperatures to prevent microorganisms from developing. Techniques such as boiling, cooking and pasteurisation use high temperatures to destroy microorganisms. Pasteurisation involves heating food quickly, without boiling, then cooling it rapidly, which will destroy most bacteria.
Which preserving techniques act on the water in food?
Preservation techniques such as drying, filtering and concentrating by boiling aim to eliminate any water available in the food.
Which preserving techniques focus on acidity?
Microorganisms cannot develop in an acidic environment. Fermentation increases acidity. It is a biological method where microorganisms convert sugars and proteins into alcohol, acid and carbon dioxide. Adding citric acid or vinegar is another way of making food more acidic.
Which preservation techniques use preservatives?
Specific substances can slow down the development of microorganisms. This is what salt does for example. The substances in the smoke used for smoking meat and fish also inhibit the growth of moulds and yeasts. 
Sugar is used to bind available water, and thus to preserve fruit in syrups and jams.
How can ultra-high pressure and irradiation preserve food?
Putting food under ultra-high pressure ranging from 3000 to 10 000 bars enables cold pasteurisation, which preserves vitamins and aromas. During irradiation, food undergoes low-level radiation, which prevents cells from multiplying.
