One of the oldest methods of preserving food is dehydration. Dehydration is the process of using heat to remove the water from the food. Dehydrated food is light and easy to carry, takes up less storage space than canned goods and doesn't require any type of refrigeration. Food drying may utilize a variety of appliances and techniques including an electric dehydrator or a conventional oven. An electric dehydrator is energy efficient, easy to use and produces the tastiest results. Using your oven, however, means you won't have to buy anything special, making it a great choice for dabblers and newbies. If you're feeling adventurous and want to try dehydrating food the old-fashioned way, you can use the heat from the sun.
Sustaining life requires water, and this is true of all life forms to some extent - including the bacteria and microorganisms that cause food to spoil. Removing water from food kills off these bacteria so the food lasts much longer than it normally would. Forcing the moisture out of food requires a combination of low heat to draw the moisture out, dry air to absorb the moisture and air movement to take the moistened air away.
Most fruits, vegetables and meats require a temperature of about 140 degrees Fahrenheit for dehydration. Herbs will keep more of their flavor if dried at a lower temperature between 95 and 115 degrees Fahrenheit. Vegetables require anywhere from three to 16 hours of drying time while whole fruits need six to 48 hours. Slicing fruits and vegetables rather than dehydrating them whole can greatly reduce drying times.
An electric dehydrator is a self-contained appliance with a heat source, a fan for circulation and multiple trays for drying many foods at one time. Better quality dehydrators also have thermostats, temperature controls and double-walled construction for more efficient energy usage. The primary benefit of a food dehydrator is that it allows you to dry food without tying up your oven for hours at a time. A dehydrator is also more energy efficient than using an oven for the same purpose.
To use an electric dehydrator, first water blanch vegetables and syrup blanch fruits. Spread the food on the drying trays in a single layer and set the dryer thermostat to 140 degrees Fahrenheit. Flip the food every few hours to make sure it dried evenly.
If you lack a dehydrator, you can dehydrate food in an electric oven so long as it can maintain the low temperatures needed to dehydrate food without cooking it. Not all modern ovens operate at low temperatures, but the oven's warmer drawer may work. Always test the temperature with an accurate thermometer before using the oven or the warmer drawer for drying foods. Note that your oven is not the most energy-efficient way to dehydrate food. It's great if you're just experimenting. If dehydrating food becomes your new favorite hobby, however, consider purchasing an electric dehydrator.
When drying foods in the oven, blanch them as you would when using an electric dehydrator. Place a cooling rack on a cookie sheet and then put the food on the cooling rack in a single layer. The rack lifts the food off the cookie sheet and promotes airflow so you don't have to turn the food. Place the cookie sheet in an oven or warming drawer preheated to 140 degrees Fahrenheit or to your oven's lowest possible setting. Prop the oven door open a few inches and blow a fan across the open door to promote air circulation. Never leave your home when the oven is on and stay alert if you have children who could burn themselves on the propped oven door.
Before electric ovens and dehydrators, people dehydrated food using the heat from the sun. Solar drying food requires a little more attention than drying foods in an oven or a dehydrator. In order to take advantage of the sun's energy for dehydrating foods, air temperatures must be at least 85 degrees Fahrenheit by noon and the humidity should be below 60 percent.
Always blanch food before drying it in the sun. After blanching, arrange the food on a screen where air can circulate around it. To prevent insects, cover the food with cheesecloth and then place it in the sun for drying. Turn the food at least once a day. Before the sun goes down, take any food that isn't completely dehydrated inside or cover it overnight to prevent re-hydration. When the food is dry, pasteurize it by freezing it for two to four days. Food dehydrated outdoors is at an increased risk of carrying bacteria, so don't skip this important step. Expect sun drying to take at least two days and possibly longer since you have less control over the drying environment.