It is quite difficult to isolate viruses on or in food. Yeasts are much larger than bacteria. However, Candida albicans , which causes thrush in infants, is the exception. The growth of some types of yeast is used to produce fermented food products. Undesired growth of some yeast in food products causes spoilage.
Molds are larger than bacteria.
The presence of mold in food can be seen as a cottony, powdery or fuzzy patch on the surface of food that may be gray, white or highly colored. The presence of mold in products causes spoilage. When some types of mold grow on grains and nuts of high moisture content, aflatoxins may form. These toxins are thought to cause liver cancer and are not easily inactivated by heat achieved during baking. Extremely moldy food should be discarded.