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When Is It Safe to Eat Moldy Food?

When is it still okay to eat moldy food? Are any molds edible? How important is it to follow those "sell by" dates printed on my egg carton? 

By
Sabrina Stierwalt, PhD,
Episode #172

Imagine 30% of all of the food produced in the U.S. each year, a total amount of food worth $48.3 billion. No, that’s not how much we consume over the holidays. That is how much food we throw in the trash according to the United Nations Environment Programme. Every year, rich countries waste about 222 million tons of food, which is almost the entire net food production of Sub-Saharan Africa.

The production of food through agriculture uses 80% of the available water supply in the U.S., meaning that uneaten food leads to a significant amount of wasted water. According to a report by the Natural Resources Defense Council, the process of “farm to fork” also uses 10% of the total US energy budget and 50% of our land. Organic waste is also the second highest component of US landfills and the largest producer of methane, a greenhouse gas an excess of which can lead to rising global temperatures.

Much of that waste happens in our homes: we throw out food because we believe it has gone bad, either because we see mold or because the food has past its printed expiration date. But are we being overly cautious? Is some of that moldy food still safe to eat? Are some of those technically expired perishables still salvageable?

Let’s look at what foods we can still eat even after they’ve “gone bad.”

What To Do When You See Mold

Molds are microscopic fungi that come in an estimated tens to hundreds of thousands of different species. In fact, there are so many varieties that scientists are still discovering new ones all the time.

Most kinds, however, have a thread or finger-like structure and resemble forests of tiny mushroom spools when observed under a microscope. This means that the spores, or the colorful heads that we see poking out of our food, are only the tip of the moldy iceberg. The mold’s stalk could potentially extend much deeper into the food and even have a root or branch system. Invisible and potentially harmful bacteria can also grow along with mold.

Some molds cause allergic reactions which can lead to respiratory problems and other, more dangerous varieties produce mycotoxins, a poisonous substance that can grow on produce and cause illness.

However, some molds are necessary for making foods we know and love to eat. For example, to make Roquefort, blue, and Gorgonzola cheeses, mold spores are introduced in the cheese making process. Brie cheese is covered in a white surface mold that is safe to eat. Other gourmet salamis come with a thin, white mold coating, which is also safe to consume, although you should toss them if you see other mold growth.

In some cases, moldy food can still be eaten safely. The best rule of thumb is that, once mold is visible on the surface, foods with high moisture content have a stronger chance of being contaminated well below the surface. So those moisture-rich foods need to be tossed. This includes lunch meats, yogurt, sour cream, jams/jellies, bread products, peanut butter, cooked past,a and leftovers of any kind.

Soft vegetables like cucumbers, peaches, and tomatoes should also be discarded, but firm vegetables like cabbage, bell peppers, and carrots are difficult for mold to penetrate and so are safe to eat if the mold is removed. The USDA recommends cutting at least one inch around and below the mold growth before consuming. Also remember not to drag the knife through the mold as you cut, or you risk contaminating the rest of the food item.

Hard cheeses can also be saved if the mold is carefully removed, but remember to then use a fresh wrapper so you do not risk transferring mold to rest of the cheese.

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About the Author

Sabrina Stierwalt, PhD

Dr. Sabrina Stierwalt is an extragalactic astrophysicist at the California Institute of Technology and Adjunct Faculty at the University of Virginia.

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