A food dehydrator is a device that removes moisture from food to aid in its preservation. Food drying is a method of preserving fruit, vegetables and meats that has been practiced since antiquity. Design Most modern food dehydrators are low-power convection ovens that use heated air flow to reduce the water content of foods. The water content of food is usually very high, typically 80–95% for various fruits and vegetables and 50–75% for various meats. Removing moisture from food restrains various bacteria from growing and spoiling food. Further, removing moisture from food dramatically reduces the weight and often volume of the food, making it easier to storage. Thus, food dehydrators are used to preserve and extend the shelf life of various foods. Food dehydrators require heat sources such as solar energy, electric power or biofuel, and vary in form from large-scale dehydration projects to do-it-yourself projects or commercially sold appliances for domestic use. A commercial food dehydrator's basic parts usually consist of a heating element, an electric fan, air vents which allow air to circulate, and food trays to lay food upon. As shown on the right, the trays most commonly have slits to provide more surface area between the food and the air. A dehydrator's heating element, fans and vents simultaneously work to direct hot air over the food, accelerate surface evaporation and warm the food causing moisture to be also released from its interior. This process continues until the food is dried to a substantially lower water content, usually less than 20%. Most foods are dehydrated at , although meats being made into jerky should be dehydrated at a higher temperature of — or preheated to that temperature — to guard against pathogens that may already be in the meat. These temperatures are similar to those used in pasteurization, and achieve similar effects. The key to successful food dehydration is the application of a constant temperature and adequate air flow. Too high a temperature or too low of airflow can cause hardened foods: food that is hard and dry on the outside but moist, and therefore vulnerable to spoiling, on the inside. Variants Solar food dehydrators Solar food drying involves the use of a solar dryer designed and built specifically for this purpose. Solar drying is distinctly different from open-air "sun drying", a simple technique that has been used for thousands of years. A good solar food dryer