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Why does food rot?What is photodegradation?How can you prevent food from spoiling?

Today’s Wonder of the Day was inspired by Kate from Waukesha , WI. Kate Wonders, “Why does food rot?” Thanks for WONDERing with us, Kate!


Whew! What"s that smell? You opened up the refrigerator door to grab a quick snack. You spied a plastic container with leftovers from your favorite meal earlier in the week. But when you opened the container, your nostrils were assaulted with a stench that killed your appetite in a matter of seconds.

What"s going on here? What you just encountered was rotten food. The process of spoiling is a natural part of the life cycle of all foods, and it"s easy to detect by smell, taste, feel, or sight. Think about the many examples of spoiled food you"ve probably seen, felt, tasted, and smelled over the course of your life.

Although rotting is a natural process that all foods eventually go through if left exposed to the elements, you definitely don"t want to eat food that you suspect is spoiled. To the contrary, you should dispose of any food you believe may be rotten, so that you avoid the possibility of food-borne illnesses.

When food is harvested, either in the form of vegetables, fruits, or meats (from animals), it becomes detached from the sources that gave it life. In other words, once you pick an apple, it begins to die immediately.

Some foods, such as fruits and vegetables, have thick cell walls that keep the food in an edible state for several days or even weeks. Over time, though, those cell walls begin to break down. When this happens, you can feel these fruits and vegetables become less solid. They may also begin to turn colors, smell bad, and taste even worse!

What causes these changes within foods? Some of the primary culprits are air, moisture, light, temperature, and microbial growth. When two or more of these culprits get together, they can accelerate the spoiling process even further.

When food is exposed to air, microorganisms can land on the food and begin their work of breaking down the food for their own uses. The presence of oxygen enhances the growth of microorganisms, such as molds and yeasts, and contributes directly to deterioration of fats, vitamins, flavors, and colors within foods through the work of enzymes.

All food is made up of a certain percentage of water. Over time, microorganisms use the water within food to fuel the chemical reactions they need to dissolve the food for energy and growth. Moisture on the outside of food also allows molds and other microorganisms to grow on the outside of food, as well as within any cracks or holes in the surface of the food, further contributing to increased decay.

When food is exposed to light, its outer layers can begin to spoil in a process known as photodegradation. Photodegradation can result in discoloration, as well as loss of flavor, vitamins, and proteins.

Temperature also plays a role in food spoilage. As temperature increases, the chemical reactions that drive the spoiling process accelerate. That"s why putting foods in the refrigerator or freezer helps to slow down the rotting process.

The process of food spoilage isn"t all bad, though. It"s a natural process that allows nutrients from the foods, as well as seeds, to be released and used again by living organisms in the environment. These processes are also key to creating some of the foods you love. While no one wants to drink spoiled milk, the souring of milk is an important step in the process of making cheese!

Since most of us do not grow our own food today, we must take steps to prevent food spoilage, so that food will last long enough for it to be transported to a store where we can buy it and bring it home to cook and eat. Scientists and researchers have helped develop many tactics over the years to fight against the main causes of spoilage, such as air, chemical reactions, and microorganisms.

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If you"ve been to a grocery store recently, you know that food comes in a wide variety of packaging. That"s not all just for show. Food packaging helps to protect it from the air and light. Controlling temperature by refrigerating and freezing foods also helps to slow down chemical reactions. Finally, the battle against microorganisms is often fought by adding chemicals known as preservatives to food. These chemicals help to inhibit the chemical reactions that allow microorganisms to break down food for energy.


Try It Out

We hope today"s Wonder of the Day didn"t spoil you! Keep learning even more when you check out the following activities with a friend or family member:

Ready for a field trip? Ask an adult friend or family member to take you on a field trip to a local grocery store. Talk with someone who works in the meat and/or produce departments. These workers have to be very familiar with food freshness. What steps do they take to make sure that all food sold is fresh and healthy? Do they ever have problems with food rotting? What do they do with rotten food?How do you keep food from rotting at your house? Talk with an adult friend or family member about the steps they take to ensure that all food is kept as fresh and as safe as possible. What are some of the methods used? Which are most effective? Which foods tend to rot fastest and need to be replaced most often?