Sun dried tomatoes are one of the most useful gourmet ingredients for cooking. They are also expensive. If you grow or pick your own (or even if you buy them) sun drying them yourself is easy to do at home.
To prepare tomatoes for drying, wash them thoroughly and remove any tough or soft spots. Depending on how big you want your final product to be, cut them in either half or quarter slices, keeping them as uniform as possible in size. Expect them to shrink to about 25 percent of their original size. There's no need to remove the skin, pulp, or seeds. All are packed with nutrition and since some of the water soluble vitamins are lost in the dehydrating process, it's better to keep them intact.
The Traditional "Sun" Method
This is the traditional method for sun drying tomatoes. Simply place the tomatoes (skin side down) on a plastic screen or drying tray. Cookie sheets work as drying trays too, but the drying process will take much longer. You'll also need to flip the tomatoes frequently to ensure they dry evenly on both sides. Don't worry if the tomatoes touch each other. Sprinkle them with a bit of Himalayan or Celtic sea salt to help draw out the moisture. Some people also like to add spices or herbs (basil) at this point. Cover the trays with cheesecloth or nylon stockings to keep the insects out, and set the trays in the sun to dry. This can take several days to a few weeks depending on the weather. Move the trays to a dry warm spot each night, or if it starts to look like rain.
The Oven/Food Dehydrator Method
If you have an oven or a food dehydrator, you'll get the same results as the traditional sun method, only a lot faster. A food dehydrator is ideal, and should be set at 135 to 145 degrees F for best results. An oven will take slightly longer than a food dehydrator, but everyone already has one, so no additional equipment is necessary. You are also likely to have to play around with rotating the trays to different racks and flip the tomatoes pieces to obtain optimal results. If using an oven, omit the cheesecloth or nylon covering and plastic trays. Use a cookie sheet or pizza pan instead. Set your oven to 135 to 145 degrees F or as low as possible. Expect 10 to 24 hours to pass before the tomatoes are fully finished drying.
Testing Their Doneness
When properly dried, your tomatoes should have a flexible, leathery texture, and if using a red tomatoes, a deep red color. Tomatoes that feel tacky, sticky, or wet in any way are not finished. Brittle tomatoes are overly dry and will have lost most of their nutritional value.
Types of Tomatoes to Use
Fresh tomatoes are 93 percent water. So although technically you can dry any variety of tomato, varieties that have a lower water content will dry out faster. The traditional paste-type red plum tomatoes (Romas) seem to work best. Other popular varieties include cherry and beefsteak. Tomatoes should be ripe, but not overly ripe.
Yields will vary according to the size and water content of the variety selected, as well as the moisture content of the finished tomato. For example, twenty pounds of fresh medium-sized tomatoes can yield approximately 1 pound of sun dried tomatoes. Five pounds of Roma tomatoes can yield approximately 2 cups of sun dried tomatoes (now you know why they are so expensive!)
Sun dried tomatoes can be used as is or re-hydrated. To re-hydrate them, soak them in water, wine, bouillon, or olive oil for 1 to 2 hours. The liquid can then also be used in cooking. If soaking them required longer than 2 hours, they should be re-hydrated while in the refrigerator. Re-hydrating them with boiling water or warm liquids will speed up the process.
Once your tomatoes are dry and cooled to room temperature, they can be stored in glass jars, Tupperware containers, Ziploc bags or they can be vacuum sealed. If using Ziploc bags, try to pack as many tomatoes into a bag as possible and squeeze out any excess air. Store your sun dried tomatoes at room temperature in a dark cupboard or pantry for up to 1 year. Sun dried tomatoes kept tightly wrapped in the freezer will stay fresh for up to 18 months.
*Tomatoes packed in oil or with garlic or fresh herbs need to be kept in the refrigerator and should be eaten as soon as possible.