Every morning the sun rises, showering the earth with invisible photons, warming our planet, and feeding our plants with energy. This last process is almost magical: plants collect and store the sun’s energy, combining it with carbon dioxide and water to create the absolute necessity of life—food. It’s no wonder that all over the world, people start their day with sun salutations.
But the sun is not just for growing our food; it’s for preserving it, too. Naturally or by intention, laying fruits in the sun is an ideal way to extend your harvest long past its annual season.
People have preserved food by solar dehydration for thousands of years. One of the earliest written accounts comes from Mesopotamia where recipes written on clay tablets dating back to 1700 BC detail the process used to preserve dates, figs, grapes, nuts, quinces, and a variety of other foods.
These methods were not isolated to the fertile grounds of the Middle East. Native Americans also harnessed the sun’s energy to preserve wild fruit, meat, and fish for the cold winter months. Many recognized that fallen fruit in the heat of the summer did not lose its edibility. Instead the flavour became sweeter and more intense. The fruit’s light weight and stability in storage made it an excellent resource for nomadic or semi-nomadic lifestyles.
Sun dried makes sense
There are many benefits to preserving food through the use of the sun:
Using the power of the sun means it’s not necessary to plug in an electric dehydrator or use electricity when the sun is shining on harvest day. With the right setup, you could preserve pounds of your harvest at no cost at all.
If correctly prepared and stored, dried fruit can last up to five years and dried vegetables 10 years or more. This makes solar dehydration the ideal way to achieve long-term storage.
Dried fruit has a naturally low pH, a low moisture content, and contains natural and antimicrobial compounds. All these factors make it an incredibly stable food with very few, if any, related food borne illnesses.
According to an article published by the National Center for Biotechnology Information, products dried using solar methods are higher in flavor and often have a higher vitamin A and C content than those preserved using conventional drying methods.
By weight, dried fruits have three and a half times the fibre of their fresh counterparts.
Mushrooms dehydrated by the sun offer a far greater source of vitamin D than any other natural source. Studies carried out by Paul Stamets of Fungi Perfecti showed shitakes exposed to eight hours of sunlight soared from 100iu/100 grams to over 46000iu/100grams. For those who live in areas of low winter daylight, or for those deficient in vitamin D, adding sun-dried shitakes to your meal could be the alternative to a daily regime of supplements.
How to get started in sun drying: direct and indirect solar dehydration
Fast-forward 3000 years from when humans first lay a fig in the sun and you’ll find solar dehydration technology remains relatively simplistic. Where we have advanced is in efficiency and sanitation.
There are now dozens of designs to choose from based on two types of drying methods: direct dehydration and indirect.
Direct solar food dryer
Direct solar food dryers are more straightforward and require less space than indirect dryers. The easiest way to construct a direct dryer is to create a frame of 2 x 2’s covered with screen, nylon, or plastic sheeting on all sides but one. The remaining side has a separate screen door to access trays of food.
Within the frame, insert one or more trays where fruit can be exposed to the sun for direct heating, but protected from insects and animals. This method works really well for tomatoes, plums, and herbs. Be sure to check on food frequently and bring trays in the house at the end of the day if drying is not complete.
There are a few drawbacks to using a direct dryer:
- Foods can take longer to process versus an indirect dryer.
- Foods can lose nutritional value due to exposure to UV.
- Molds can develop if moisture is not removed quickly enough.
One solution to these problems is adapting a solar oven for dehydration. Designed to maximize the power of the sun and reduce drying times, some solar ovens now come with optional dehydration kits for sun drying food.
Indirect solar food dryer
An indirect dryer can often take up more space due to its two-chamber design: one chamber where the food is placed on trays or sheets and another for solar absorption. This type of dryer relies on air heated by the sun in its second chamber.
The collector box is a long, shallow wood frame located beneath and at an angle to the drying chamber. The box is lined with solar absorbers, such as dark-colored window screen or layers of metal lathe. The roof of the collector box is either glass or plastic glazing.
While operating, the bottom of the dryer’s box remains open to draw fresh air in and over the absorbers. As the air moves up, it can heat up to 20 degrees warmer than outside temperatures. The hot air naturally moves up and into the chamber that holds the food, and out through vents on the roof, carrying with it the moisture collected from the prepared fruits.
An indirect dryer can process large amounts of food at once and offers more consistent temperatures—making the processing quicker.
Tips for sun-drying your food
Whether you’re employing a direct or indirect dryer, there are a few considerations to avoid costly mistakes.
- Ensure you’re monitoring temperatures inside the dehydrator. Food is best dehydrated between 120-140 degrees and will cook at 180 degrees.
- If dehydrating isn’t complete, bring trays of food indoors in the evening to avoid cool, moist air that can rehydrate what you’ve processed earlier that day.
- You may find that lower trays dry faster than upper trays. To avoid this, check that food is drying consistently, moving trays if necessary.
- Proper food preparation will save time. To ensure a fast and even process, slice food thinly and consistently. Varying thicknesses will cause much frustration, since you’ll constantly have to check and remove pieces that are done ahead of others. Food will appear dry but pliable when ready and will not bead with moisture when torn.
Overall, dehydrating food using the sun’s energy is an inexpensive and rewarding method to preserve the harvest bounty you’ve been growing all season long. Packed with vitamins and fiber, the taste of a sun-dried tomato on a cold January day will bring you right back to the gardens of summer.
Editor’s note: This article has been updated for accuracy and comprehensiveness.