Answer:
Bacteria
Microscopic bacteria cause food to spoil. These tiny organisms, called spoilage bacteria, consume unprotected foods and produce waste products. As long as nutrition and water are present, bacteria will multiply, sometimes rapidly. Bacterial waste is the cause of the foul smell and rotten appearance of spoiled food. Surprisingly, rotten food will not necessarily cause illness if consumed. Instead, other bacteria species called pathogenic bacteria are the cause of foodborne illnesses like salmonella and E. coli. It's possible for food to look and smell safe, but still contain dangerous levels of pathogenic bacteria.
Incorrect Storage
Improper food storage is a leading cause of spoilage. If your house is warm and humid, fruits and veggies left in the open will spoil quickly. A refrigerator temperature above 40 F allows for the growth of spoilage bacteria. Food items should be stored separately in tightly sealed containers. Designate one drawer for meats, one for cheeses and one for vegetables. Check your refrigerator foods every day. If one food starts to spoil, remove it immediately. The spoilage bacteria may spread from the bad food and contaminate everything else.
Dehydration
Bacteria need moisture, oxygen and the proper temperature range in order to multiply. Dehydration is the process of removing moisture from foods, thereby slowing or stopping the growth of spoilage bacteria. To dehydrate food properly, you need low humidity and a source of heat. You can use a conventional oven set to warm with the door open or an actual food dehydrator. The food needs to be heated to about 140 F. Dry, circulating air helps draw moisture out of the food. Dehydration also makes foods lighter, smaller and easier to store and transport.