Drying foods preserves them by removing water in foods that is required for microbial growth and for most chemical spoilage reactions. It is important to remove enough water to prevent microbial growth for safety. In ancient times the sun and wind would have naturally dried foods. Evidence shows that Middle East and oriental cultures actively dried foods as early as 12,000 B.C. in the hot sun. Later cultures left more evidence and each would have methods and materials to reflect their food supplies; fish, wild game, domestic animals, etc. Vegetables and fruits were also dried from the earliest times. The Romans were particularly fond of any dried fruit they could make. In the Middle Ages purposely built "still houses" were created to dry fruits, vegetables and herbs in areas that did not have enough strong sunlight for drying. A fire was used to create the heat needed to dry foods and in some cases smoking them as well.
Drying foods safety concerns: Dry foods are safe from foodborne illness because they lack the water needed to permit growth of microorganisms. The main concern for the safety of dried food is moisture. Dried foods that have picked up moisture begin to be pliable (softer). If a dried food gets wet or picks up enough moisture it can start to permit microbial growth. Molds which cause only spoilage, are the first to grow. Always discard moldy dried foods. When moisture is obviously present foodborne illness bacteria can begin to grow. Always discard these foods.
The next major safety concern is in the drying process itself. Drying raw meat is a concern. Often the drying temperature is not high enough to destroy food borne illness bacteria. A few foodborne illness bacteria, like Salmonella and E. coli can survive short periods (days) of being dry to cause illness once consumed. There are several Extension drying jerky publications available to provide recommendations. Vegetables are best blanched before drying. This will help destroy any microorganisms on them and destroy spoilage enzymes. Fruits are safer to dry since they are high acid. With all of these foods, its best NOT to mix them in the same drying apparatus.
Resources for Drying foods:
USU Extension: Home Drying of Foods 1994 - this is an older comprehensive publication, but still up to date with safe recommendations
USU Extension: Kathy Riggs PowerPoint Presentation on Drying Foods
USU Extension: Venison - has venison jerky recommendations
NCHFP Resources - Dehydrators, fruit and vegetable leathers, jerky, and storing dried foods.
Clemson University Extension: Drying Vegetables
Colorado State University Extension: Drying Fruits