What causes food spoilage?

Germany

Food spoilage can be caused by a combination of various factors such as light, oxygen, heat, humidity and/or all kinds of microorganisms.
Therefore in general every kind of food should be stored in a dark dry place and at a proper temperature to keep its quality, whether fruits, vegetables, cereals, meat, fish, milk or milk products. The industry also has many techniques for protecting food from spoilage:

• for avoiding light - photoresistant packages, dark bottles for oils
• for avoiding oxygen - canning, vacuum packaging
• for avoiding heat - cooling
• for avoiding humidity - vacuum packaging
• for avoiding the development of microorganisms - pasteurization, UHT, freezing, chemical preservatives, irradiation

See also:

Food production: http://www.foodexperts.net/technology-production/index.php
and
Question: What types of food should not be exposed to sunlight?