Blanching (heating in boiling water or steam) is the pretreatment method of choice for vegetables. Almost all vegetables should be blanched before drying to destroy the enzymes that make vegetables deteriorate. Blanching keeps vegetables from browning, becoming bitter, or developing off flavors. Blanching also cleans and softens vegetables and makes them easier to rehydrate later. Although you can use either boiling water or steam for blanching, vegetables lose more nutrients during boiling.
Use a steamer or make a steamer out of a kettle with a tight-fitting lid. Place a colander, wire basket, or sieve inside the kettle. Make sure the food will be above the water level. Add 2 inches of water to the kettle and heat it to boiling. Place the container with the loosely packed food in the steamer, cover the kettle tightly, and continue boiling.
Fill a kettle with enough water to cover the food. Bring the water to a rolling boil and gradually stir in the food. Cover the kettle tightly and boil. You can reuse the water when blanching more of the same food, adding more water as necessary. If the water appears dirty, replace it with clean water.
Determining Blanching Times.
Blanching times vary with altitude (higher altitudes require longer blanching times), the type and texture of the vegetable, the amount of vegetable, and the thickness of the pieces. Generally, vegetables should feel and taste firm yet tender. They should not be fully cooked, but they should be heated all the way through. Test the food by cutting through a piece. If sufficiently blanched, it will appear cooked (translucent) nearly to the center.
The drying guidelines suggest blanching times, but you should test the food frequently to avoid over- or underblanching. Underblanching may cause deterioration in storage, poor rehydration, or bad color. Overblanching makes vegetables lose color, flavor, and nutrients and gives them poor texture after rehydration.
Drain vegetables by pouring them irectly on the drying trays. If you plan to reuse the water, place a large pan under the trays. Wipe the bottom of the drying tray with a clean towel to remove excess water. Draining the vegetables on one tray and then transferring them to the drying tray results in unnecessary handling. Immediately transfer the blanched vegetables into the dehydrator so drying can begin while the vegetables are still warm.
Drying Canned Fruits and Frozen Vegetables
Using canned fruits is a quick way to prepare fruit for drying. Drain the syrup, rinse the fruit, and cut it into 1/2-inch slices, if desired, then dry as usual. Drying times will be longer than for fresh fruit because the canned fruit will contain absorbed syrup. Dried canned fruit resembles candied fruit and can be used in similar ways. Likewise, frozen vegetables can be thawed, drained, and dried.Blanching was taken care of before freezing.