Dehydrating basics

01 — The temperature rule

Fruits and vegetables dry at 140°F, herbs cooler, and meat gets heated first

The National Center for Home Food Preservation (NCHFP) notes that dehydrators are designed to dry food fast at 140°F, and Colorado State University Extension gives the same 140°F figure for fruit in a dehydrator or oven.

Herbs run cooler. NCHFP sets the dehydrator thermostat at 95 to 115°F for herbs, up to 125°F in humid areas, and says most batches take 1 to 4 hours. NCHFP warns that basil, oregano, tarragon, lemon balm, and the mints hold a lot of moisture and will mold if not dried quickly.

Meat follows a different rule. USDA FSIS explains that while meat dries, the evaporating water absorbs most of the heat, so the meat stays relatively cool until most of the water is gone, and bacteria become much more heat resistant once dry. Heating the strips to 160°F first, while they are still wet, kills bacteria before that resistance builds.

NCHFP gives two ways to do that heating. You can bring the strips and their marinade to a boil and boil for 5 minutes before draining and drying at 140°F, or you can dry first and then heat strips 1/4 inch thick or thinner for 10 minutes in an oven preheated to 275°F. NCHFP also notes that raw poultry is generally not recommended for jerky, and that pork or wild game should first be frozen at 0°F or below for at least 30 days, in pieces 6 inches thick or less, to kill trichinella. Freezing does not kill bacteria, so the heating step still applies.

02 — The process

Thin, even pieces in a single layer dry at the same pace

Even drying starts with even slicing. Colorado State University Extension gives 1/8 to 1/4 inch for fruit slices such as apple rings, and NCHFP says to slice jerky meat no thicker than 1/4 inch. Pieces of one thickness finish together; a thick piece in a tray of thin ones stays moist in the middle after the rest are done.

Lay pieces in a single layer with room for air to move between them. Colorado State recommends stirring food and turning large pieces over every 3 to 4 hours. Fruit scorches easily near the end of drying, so check more often in the last hours.

Light-colored fruit such as apples, apricots, peaches, and pears darkens as it dries unless it is pretreated. Colorado State University Extension gives three dips, each a 10-minute soak: 2 1/2 tablespoons of pure ascorbic acid crystals per quart of cold water, 1 teaspoon of citric acid per quart of cold water, or equal parts lemon juice and cold water. It also describes a sulfite dip but does not recommend it for anyone with a known sulfite sensitivity, because sulfites can set off asthmatic reactions.

Each food has its own finish. Fruit is done when it is leathery and pliable, vegetables when they are brittle, and NCHFP says jerky is dry when a test piece cracks but does not break when it is bent. Marinate meat in the refrigerator, as FSIS advises, and do not reuse the marinade.

03 — Where food can dry

A dehydrator or a low oven works for everything; only fruit dries outdoors

NCHFP says the high sugar and acid content of fruit makes it safe to dry outdoors when conditions are favorable: at least 85°F, higher being better, with humidity below 60 percent. It takes several days, and fruit should be covered or brought in at night because cool night air adds moisture back.

Indoors, a kitchen oven can stand in for a dehydrator. Montana State University Extension says the oven must have a setting as low as 140°F; if it does not go that low, the food cooks instead of drying. Prop the door open 2 to 6 inches for air circulation, and a fan outside the oven near the door helps. Expect it to take twice as long as a dehydrator and to use more energy.

Vegetables are low in sugar and acid and meats are high in protein, which raises the risk of spoilage. NCHFP does not recommend drying either outdoors, with one exception: beans left to dry on the vine. Those beans need pasteurizing to kill insects and their eggs, either sealed in freezer bags at 0°F or below for at least 48 hours, or spread in a single layer for 30 minutes in an oven preheated to 160°F.

04 — Storage

Airtight, cool, dark, and checked often

NCHFP recommends clean, dry home canning jars, plastic freezer containers with tight lids, or freezer bags, and calls vacuum packaging a good option. Glass has an advantage: moisture that collects inside is easy to see. Keep containers in a cool, dry, dark place, because higher temperatures shorten storage life.

NCHFP gives a storage range of 4 months to 1 year for dried foods. Most dried fruit keeps about 1 year at 60°F and about 6 months at 80°F, and dried vegetables keep about half as long as fruit. Fruit leather keeps up to 1 month at room temperature, or up to 1 year frozen.

Jerky has the shortest shelf life. USDA FSIS says home-dried jerky can be stored 1 to 2 months, and NCHFP is more conservative: two weeks at room temperature in a sealed container, with the refrigerator or freezer for anything longer.

Food that looked bone dry can still take on moisture, so check jars often. NCHFP says food affected by moisture but not spoiled should be used right away or dried again and repackaged. Moldy food should be discarded.