From the moment a fruit or vegetable is harvested, it begins to decay. Microorganisms in the environment rush to take up residence, feeding on moisture and nutrients. At the same time, chemical reactions break down cells from the inside out. In nature, speedy decomposition is a positive thing, allowing plants to get their seeds into the soil. In the kitchen, on the other hand, we prefer to stall this process as long as possible.
Microorganisms Are Everywhere
The bacteria, molds and yeasts that cause spoilage in plant foods need water and nutrients to grow and reproduce. With an average water content of 90 percent or more, fruits and veggies are natural magnets for microorganisms and spoil quickly. The typical signs of decay in fruits and veggies past their prime -- bruises and blemishes, mold and slimy patches -- render them unappetizing and often smelly. Preservation techniques, such as dehydration, work by depriving microbes of water. Blanching kills many spoilage organisms. Adding sugar or salt to foods can also inhibit their growth.
Excess Moisture Invites Rot
If you wash produce and store it wet, you make it even more inviting to spoilage bacteria. So store fruits and vegetables dry, and wash them just before use. If you want to wash produce first, thoroughly wipe or spin it dry before refrigerating. Store refrigerated produce in sealed crisper drawers where humidity levels will remain relatively constant. Enclosing fruits and veggies in cloth or perforated plastic bags that allow air circulation also discourages moisture buildup.
Temperature Extremes Promote Decay
Because extremes of hot and cold accelerate spoilage, fruits and veggies stay fresh longest when stored at cool temperatures. The higher the temperature, the faster decay will occur. When fresh produce is frozen, the water inside plant cells forms ice crystals, which expand and rupture the cell walls. In addition to the negative effect this has on color, texture and appearance, cold damage also makes produce more attractive to spoilage microbes. Most fruits and vegetables can be kept for a few days at average refrigerator temperatures from 35 to 40 degrees Fahrenheit, but a few -- including bananas, lemons, squash and tomatoes -- are susceptible to cold damage at temperatures lower than 50 degrees.
Oxygen Exposure Hastens Decomposition
If you've noticed how quickly the flesh of an apple turns brown after being exposed to air, you've seen oxidation in action. Some chemicals naturally present in food, called oxidizing enzymes, react to oxygen and speed up the spoilage process upon contact with air. In addition to their need for water, molds, most yeast and many bacteria require oxygen to thrive. The more they get, the faster these microbes work. At best, oxidation undermines the eye appeal of affected fruits and veggies; at worst, it is often accompanied by unpleasant tastes and odors. As well as killing spoilage microbes, blanching also inactivates these enzymes, preventing or arresting oxidation.
- Food Safety Site: Clemson University Extension: Describe Why Food Spoils
- University of Nebraska-Lincoln: UNL Food: Food Poisoning (Foodborne Illness)
- United States Department of Agriculture: Food Safety and Inspection Service: Refrigeration and Food Safety
- Virginia Tech: Virginia Cooperative Extension: Using Dehydration to Preserve Fruits, Vegetables, and Meats
- Colorado State University Extension: Guide to Washing Fresh Produce
- University of Minnesota Extension: The Science of Freezing Foods