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?
Cooling and freezing use low temperatures to stop the development of microorganisms.
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 preservation techniques act on the water content?
Preservation techniques such as drying, filtering and concentrating by boiling aim to eliminate any water available in the food.

Which preservation techniques focus on acidity?
Fermentation increases acidity and prevents undesirable microorganisms from developing. Fermentation is a biological method where microorganisms convert sugars and proteins into alcohol, acid and carbon dioxide. Other techniques involve adding citric acid or vinegar. Fermentation is a means for preserving food, but also for changing its taste and flavour.

Which preservation techniques use preservatives?
Specific preservatives can slow down the development of microorganisms. Salting binds the water in food, rendering it more unavailable for microorganisms. The smoke used for smoking food contains substances that 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?
Subjecting food to 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.