When Is It Safe to Eat Moldy Food?

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.

How to Avoid Moldy Food

So how can you keep mold growth to a minimum? Mold likes humidity, and although mold grows best in warmer temperatures, it will still grow in places that are cold if they are also moist, like the refrigerator. The best way to stave off mold is to properly store any perishables – don’t leave food that requires refrigeration out at room temperature for more than two to three hours – and to eat foods before they have a chance to grow mold. For example, leftovers, even when stored at refrigerator temperatures, should still be eaten within three to four days.

The USDA recommends cleaning the inside of your refrigerator once every few months with 1 tablespoon of baking soda dissolved in water. If you find a moldy item, that is a good time to clean because mold spores can transfer to other foods through the air. Mold spreads particularly fast among fruits and vegetables in the same drawer. To minimize the transfer, the USDA further suggest making sure food is covered.

Also don’t sniff the moldy item! Any bacteria present could enter your nose and lead to respiratory problems.

Check out the Nutrition Diva’s nine tips for reducing food waste before your food gets moldy, including planning your meals ahead of time.

Should I Really Follow Expiration Dates?

We have all likely performed the sniff test on our milk. Can I get one more bowl of cereal or one more cup of coffee out of this milk? What if the carton is past its sell by date?

We often wrongly assume that food items should never be consumed after any date printed on their container. However, only infant formula is required by federal law to have an expiration date. Thus most printed dates are not meant to reflect safety standards but instead are meant to tell you when the product will be of the best quality.

It is generally a good idea to follow “use by” dates on food, although many foods are still safe to eat after their “use by” date if stored properly. However, these dates are moot if food that should be refrigerated is left out for more than two to three hours, even if it is re-refrigerated later.

Dates marked “sell by” are much more flexible in their shelf life once you have purchased them. You should always purchase items before their “sell by” date, and the USDA has a handy table, which details the safety period for different foods beyond their those dates once you have brought them home. For example, expiration dates on eggs—which are not required by federal law but are mandated in a few states—can be considered sell by dates. Once you purchase eggs before the date printed on the carton, they are safe to keep in your refrigerator for three to five weeks (which usually surpasses the sell by date) before they need to be tossed.

Keep in mind that both “sell by” and “use by” dates will be drastically shortened if sealed packaging is opened. Freezing a product before it’s window of freshness, on the other hand, will further keep the product safe to consume indefinitely, but only until it is thawed at which point it should be eaten within 24 hours.

There are only a few foods that won’t eventually go bad, like honey which has been found in the ancient tombs of Egypt. So it is wise to pay attention to any warning signs. Spoilage bacteria can cause unusual odors, flavors and appearances, so if something seems off, stop eating!

Until next time, this is Sabrina Stierwalt with Ask Science’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Ask Science on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.com. 

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