Mold has little trouble growing on bread that has remained on the shelf past its prime, but not all molds are created equal. Some bread molds can emit dangerous and potentially deadly toxins. By learning to identify these dangerous fungal varieties, you can potentially save yourself from serious illness or even disease.
Mycotoxins are the toxins that make some molds dangerous. The Environmental Protection Agency has determined possible links between mycotoxins and certain cancer, so excessive exposure to these toxins can actually endanger a person's life. Molds containing mycotoxins are called toxigenic molds. Non-toxigenic molds can make a person ill, but seldom prove fatal. As a result, only toxigenic molds can accurately be labeled as "deadly," and even then, only prolonged and excessive exposure can potentially shorten a person's life.
Penicillium is one of the most common molds found in bread. Mold spores grow on bread that has become moist, and you can spot active mold by its fuzzy appearance. It can appear in shades of light blue, gray and white. It grows best in cold temperatures, so it may appear on breads that have been refrigerated. Over time, Penicillium can develop mycotoxins, making it a potentially dangerous mold.
Aspergillus is another mold that commonly grows on bread, some strains of which can develop dangerous mycotoxins. Under a microscope, Aspergillus has the appearance of a flower, but on bread, it has a fuzzy appearance. Since Aspergillus has more than 150 known species, its colors can vary but it commonly has a pea-green or yellow appearance. Not all species of Aspergillus are toxigenic, but many (including A. flavus) can release mycotoxins, so avoid eating any bread with signs of Aspergillus.
Many other molds grow on breads, but most are not deadly. Many foodborne molds are allergenic, meaning that allergy sufferers may experience temporary symptoms related to their allergies, like upper-respiratory problems. Common food molds include Cladosporium, Alternaria, Botrytis, Geotrichum, Monilia, Fusarium, Manoscus, Mortierella, Oidium, Mucor, Neurospora, Oosproa, and Rhizopus. Specifically, Rhizopus stolonifer is sometimes referred to as black bread mold. Black bread mold has a fuzzy, blue or green appearance like other bread mold, but also contains black splotches.