Unwanted microorganisms can cause food to be contaminated. The contamination is usually natural, but it can also be artificial. Natural contamination is when microorganisms attach to food during its growing stages. For example, Fruits are often contaminated by yeasts, which ferment the fruits' carbohydrates. Artificial contamination is when food is improperly handled or processed.
When food is called "spoiled", it usually means that there is decay or decomposition of an unfavorable nature. Foods unfit for consumption are not considered spoiled. Spoiling could be caused by one or more of these:
Food spoilage is the result of a metabolic process which causes food products to become unpalatable or inedible for human consumption because of changes in the sensory attributes.