The abundance of online resources that students have access to makes it difficult
to determine whether the information they find is accurate. Several online
sources have claimed that hamburgers from fast-food chains do not
decompose, and we developed two exercises that allow students to (1) test this
claim, (2) learn about fungi, and (3) reflect on their eating habits. In both
exercises, we inoculated fast-food items with the fungus Rhizopus stolonifer.
The first exercise was a controlled experiment with hamburgers, and the
second was a screening trial in which all students brought in their own fast-food items. In both exercises, animal-based products and fatty baked products
(e.g., biscuits) allowed R. stolonifer to grow, while condiments and bread
products tended to inhibit growth. Our students indicated that they would be
more critical of online information and that they would eat less fast food.
These exercises met our objectives and engaged our students, and we
encourage others to develop exercises that examine online claims.
Key Words: Claim evaluation; fungi; fast food; inquiry-based learning; Rhizopus
Use of online sources can have a substantial influence on student perceptions and knowledge (Metzger et al., 2003; Metzger, 2007). Online
sources that propagate misconceptions, whether intentionally or not,
can be pernicious. Persistent misconceptions can be deleterious for
public health, for instance with nutrition, antibiotics, and vaccination
(Wansink, 2006; Barbacariu, 2014; Carter et al., 2016).
We used two types of exercises in an introductory college biology
lab to test the veracity of a common online claim that fast food does
not decompose while also teaching college biology students about
fungi. Several websites have recently claimed that hamburgers from
one or more prominent fast-food chains can last a year or longer without decomposing, even remaining “edible” (Little, 2014; Jewell, 2015;
LaCapria, 2016). These websites assert or imply that if fast food does
not decompose, then fast food is not digestible or a healthy product
that their readers should be feeding themselves or their children.
The most common explanations for the lack of decomposition refer
to these products containing “chemicals” or “fake” ingredients that last
forever. These explanations and other news reports may contribute to
a public conception that fast food is “fake food” (Stempel, 2011;
Andrews, 2014). Our college students were largely familiar with the
supposed longevity of fast food (see below), but, like other members
of the population (Paeratakul et al., 2003; Bowman & Vinyard,
2004), they still claimed to eat fast food regardless. These websites
have drawn the attention of the chains themselves, some of which
have offered rebuttals such as the food items being dehydrated to
the point that fungi and other decomposers cannot grow (Little,
2014). The claims have also been tested by the Food Lab blogger
Kenji López-Alt (López-Alt, 2010, 2016), who concluded that
hamburgers (both purchased and homemade) are too dry in an
open-air environment to grow mold but can grow mold in a moisture-
We selected fungal growth as a proxy for decomposition because
it was an opportunity to show students that fungi are ubiquitous, ben-
eficial, and important but greatly underrepresented in biological edu-
cation and general public knowledge. Some 100,000 fungus species
have been described (Chapman, 2009), and they function as decom-
posers, symbionts, pest control agents, and food sources in virtually
every ecosystem on earth (Ferron, 1978; Gianinazzi et al., 2010;
Norris et al., 2011). Fungi benefit humans by providing medicinal
compounds (Kück et al., 2014), and many cheeses and breads –
and all beers, wines, and spirits – would not exist without fungi.
For all their benefits, they can also be detrimental as agents of wildlife,
plant, and human diseases (Fisher et al., 2012) and because they can
spoil natural products, including food, by decomposing them or pro-
ducing harmful toxins (U.S. Department of Agriculture, 2013).
Our two exercises included a controlled experiment inoculating
hamburgers with mold and an inquiry-based screening exercise inoc-
ulating dozens of food items with mold. Similar exercises inoculating
bread are used widely in “fungus labs” in biology courses (e.g., Perry
et al., 2006); however, to our knowledge, lab manual exercises rarely
The American Biology Teacher, Vol. 81, No. 5, pp. 360–365, ISSN 0002-7685, electronic ISSN 1938-4211. © 2019 National Association of Biology Teachers. All rights
reserved. Please direct all requests for permission to photocopy or reproduce article content through the University of California Press’s Reprints and Permissions web page,
www.ucpress.edu/journals.php?p=reprints. DOI: https://doi.org/10.1525/abt.2019.81.5.360.
Does Fast Food Last Forever?
Exploring the Mold Myth
• EVAN LAMPERT, HOLLY MUNRO