A General Guide To Drying

Introduction

Early humans were constantly on the move seeking food and whatever they picked or killed had to be consumed quickly before spoilage set in. At some point, however, one observant hunter/gatherer must have noticed that when the heat from the sun and the breeze from air currents caused the moisture to quickly evaporate from a plant or animal that had been harvested, the food didn’t spoil. They didn’t know why this happened, but they did understand that now they could keep that food for later use. The ramifications of this were staggering. People could now stay in one place and branch out for the hunt or the gathering expedition and bring the bounty home and let the sun and wind do the work. This was the earliest form of food preservation and the beginning of civilization.

While technology has vastly changed the way we dry food, the principles have remained the same throughout time. Plants and animals contain moisture, and after the plant or animal has been harvested, this moisture allows the growth of bacteria, molds, and yeasts, which cause spoilage. Removing that moisture, a process called dehydration, stops the process of decomposition and allows the food to retain its nutritive value— in some cases, for a very long time.

We still hunt and gather, and if you’d like to try your hand at drying the blackberries you’ve picked, meat from your successful hunt, the bananas that were on sale, the pinto beans you grew, or the herbs from your windowsill garden, you can. You can dry almost anything. It’s easy and you’ll save a considerable amount of money compared with what you’d pay for dried foods at the store. Ready to begin? Here we go.

Different Methods of Drying

There are so many different ways to dry foods that you’re almost certain to find the right one for what you want to do. Foods can be dried outdoors and indoors. Outdoors, you can take advantage of air movement and the heat of the sun; indoors, you can use a dehydrator, microwave, oven, and even the air itself. It might seem truly odd, but people have tried to dry food in the clothes dryer. Don’t! The idea of tumble-drying jerky makes the head spin. Also, if you have forced-air heat, resist the impulse to spread your apple slices on an air vent. It might work for drying socks, but the dust and other contaminants in the air aren’t good for food. Learn more about drying.

Air Drying

In warm climates with low humidity, outdoor air drying works quite well for certain foods, including herbs, mushrooms, green beans, onions, and garlic. These foods are hung away from the sun in a place with good air circulation. Moisture is the enemy and it’s essential to bring drying foods indoors overnight if there’s any chance of dew or increased humidity, as this can cause the foods to turn moldy and spoil.

To prepare green beans and mushrooms for outside air drying, string them together. It’s the same procedure you’d use to string popcorn on a Christmas tree. Use a sturdy needle and strong thread. When you’ve got a string completed, hang it from a hook out of the sun and in a place with good air circulation.

Onions and garlic can be braided before hanging. Just remember to leave the long stems attached so you’ll have something to braid.

Air drying also works indoors and you don’t have to worry about a nocturnal rainstorm or sudden jump in the humidity. Herbs, garlic, and onions are good candidates for this type of home food preservation.

Herbs are an essential part of the home food preserver’s pantry. Air drying works well for herbs, which shouldn’t be dried in the sun. You’ll need scissors, small paper bags (lunch size), large paper clips or Christmas ornament hangers, and yarn or twine.

Herbs need to be completely dry before you begin the drying process (which is sort of a paradox!) because the slightest bit of mold will ruin them. Cut a stem about 6 inches (15cm) long and remove the lower leaves. If the herbs are dusty, rinse them off, but be sure they’re completely dry before you work with them. You can set a hair dryer on low and wave it around the herbs to make sure.

Use the twine or yarn to bundle several stems together and then insert the bundle into a paper bag. Tie the bag around the stems and be sure the herbs aren’t touching the sides of the bag. If they do, they might adhere to the bag during the drying process and refuse to separate.

Bend a large paper clip into a hook or use a Christmas ornament hanger to snag the twine around the paper bag. Hang the bag away from light in an airy location. You can run a string across a doorway in a seldom-used room and hang the bags from the string. The bags will protect the herbs from sunlight and dust, and they’ll also catch any stray leaves that decide to jump ship. It will take about 2 weeks for the herbs to air dry.

When they’re dry, you can separate the leaves from the stems and store them away from direct heat or sunlight in a glass jar with a secure lid. They’ll keep for about 1 year.

Vine-drying is another form of air drying. Numerous varieties of beans, including kidney, pinto, navy, Great Northern (white), and soy, and even lentils can simply be left alone until their vines have died a natural death and the pods have dried. Use the shake, rattle, and roll test. When you shake the pod and it rattles, you’re ready to roll. The vines can then be pulled and the beans shelled.

Sun Drying

Chili peppers drying on fabric in the sun by a car

Sun drying uses the sun’s heat and air movement, and it’s the most inexpensive method for drying foods. Because of their high sugar and acid content, fruits are recommended for sun drying. Vegetables and meat products are low-acid and low-sugar foods and they’re not recommended for this process. They can easily become reservoirs for harmful bacteria and spoilage.

Apricots and peaches set out to dry on wooden, slatted trays used to be a common sight in California orchards at picking time. Today, the orchards are fewer and outdoor drying is rarer, but if you venture out into the country, you might be lucky enough to spot some.

Drying outdoors requires several consecutive days of high temperatures—from the mid-90s to 100°F (35°C to 40°C)—accompanied by low humidity (below 60%) and brisk winds. If your climate lends itself to outdoor drying and the air is clean where you live, you might want to give it a try.

You’ll need drying trays, which are wood frames with wood slats far enough apart to allow the air to circulate but close enough together to keep the food from falling through the cracks. Stay away from redwood or other evergreen woods. These can cause the fruit to have an off-putting flavor and can also stain the fruit. Stainless steel, plastic, and Teflon-coated fiberglass trays can also be used, but avoid hardware cloth, which is a galvanized metal cloth covered with cadmium or zinc that can leave harmful residues on your food. Additionally, copper or aluminum aren’t recommended. Copper destroys Vitamin C and increases oxidation, while aluminum discolors and corrodes.

You’ll need bird netting or cheesecloth to keep dust and insects from the food. If you’ll be drying light-colored fruits—such as peaches, pears, or apples, the best candidates for outdoor drying—you’ll need ascorbic acid (vitamin C) or a commercial anti discoloration preparation and pans for holding the anti discoloration agent.

Light-colored fruits dried outdoors used to be dusted with sulfur to keep them from darkening during the drying process. While the product was visually appealing, keeping apricots and peaches a deep orange, this process is no longer recommended, as sulfur can have serious health consequences in individuals with a sensitivity to sulfites. Instead, you can pretreat light-colored fruits with a commercial anti discoloring preparation, ascorbic acid, or vitamin C. However, the dried fruit will be darker than sulfured fruit.

Solar Drying

This is one step up from sun drying. A solar dryer is a structure that uses reflectors to intensify the sun’s heat and a ventilation system that increases airflow to speed up the drying process. This is useful if your area tends to be more humid or if temperatures aren’t optimal for sun drying, although it’s still iffy as a solution. Foods that are suitable for sun drying, such as fruits, are good choices for solar drying. Even though solar drying speeds up the process, it’s not reliable enough to ensure that vegetables won’t become contaminated by bacterial growth and spoil. If you’re handy with materials, you can make your own solar dryer using found materials. For example, gardeners who like to get a head start on the season are likely to use a cold frame. A cold frame is simply a wooden box minus the top and bottom. It’s set outdoors on the ground and plants are set inside it for shelter. The top is usually an old window that’s attached with a hinge and propped up with a piece of wood during the day and closed down at night. It provides protection from wind and cold.

Lining this with aluminum foil and propping the glass open to allow air circulation will serve as a makeshift solar dryer. See Appendix F for further information.

Oven Drying

This takes the drying process indoors where climate doesn’t matter. It also expands your options because you can dry vegetables, fish, and herbs as well as make fruit leather and jerky by this method. The major drawbacks to drying foods in the oven are limited space and the cost of energy. You can generally dry about 5 pounds (2.3kg) of food at a time and the only other items you’ll need are a wooden spoon or an oven mitt to prop the door open a smidge while the foods are drying and a thermometer to check the internal temperature. You want to keep that at 140°F (60°C). You’ll also want to check to be sure you can set your oven to this temperature. Air circulation is essential, thus the slightly open door. Be sure there are at least 3 inches (7.5cm) of free space all around your trays to let the air circulate freely. Heat is required, thus the thermometer. You’ll need to keep an eye on the temperature and turn it up or down accordingly to maintain an even flow.

The temperature is the warmest closest to the heating element. If you have a gas oven with a pilot light, that might be enough to give you the temperature you need. The way to check is to put a thermometer on the top rack and close the door. Check in 1 hour and see what the reading is. If it’s not high enough, you’ll need to turn the oven on warm. Check the temperature again after 30 minutes.

Oven drying isn’t difficult, but it requires some finessing to settle at the proper temperature. You might need to do some fiddling with the temperature control until you hit on just the right setting. Do this part of the preparation work before you commit food to the oven. You can’t rush the process. If you try to speed it up by increasing the temperature, you’ll end up cooking your food rather than drying it. There’s also something called case hardening, which occurs when the outside of the food cooks, thus preventing the moisture inside from escaping. This will cause your food to mold. Increasing the airflow to move moisture away from the food is the only option if you’re growing old sitting by the oven waiting for things to dry, and if you have a convection oven, using this feature can help. Regardless, it takes as long as it takes.

Trays

Rows of drying persimmons on trays on a rooftop

Air circulation is essential to getting a good product, so you’ll need trays made with wood slats or stainless steel screening. Most ovens have two or three racks, and if you use all three, you’ll have pretty close to a full load without rigging an additional rack. Cookie sheets and other solid trays aren’t suitable because they block the airflow. Be careful about the materials you use when making your trays. Keep to stainless steel or wood to prevent harmful chemicals from coming in contact with your food. Aluminum, copper, vinyl, fiberglass, and galvanized metal should be avoided.

Method

As you’ll see shortly, oven drying is best begun early in the day. Place the cut food in a single layer on each tray and place each tray on an oven rack. Be sure there’s room for the air to circulate around each piece of food. Prop the door open so the air can circulate, but keep an eye on the thermometer so the temperature remains between 140°F and 160°F (60°C and 70°C).

You can speed up the process a bit if you have a small electric fan to set up so the stream of air blows into the oven. Once you’ve got everything nicely settled, set the timer for 30 minutes.

When the timer buzzes, it’s time to rotate the racks. Move each rack down one space and put the bottom rack on the top. Reset the timer. Each time you check, repeat this process so every rack will have equal time at every position. This will correct for any temperature differences inside the oven.

You can also take this opportunity to turn the food over so it dries more evenly. You can expect the process to take several hours and vegetables can take up to 12 hours. This is why it’s best to get an early start. You don’t want to be rotating racks and flipping food late at night. Read up on drying.

Fruit Leather

Get out those cookie sheets again! (Be sure they’re rimmed.) Smooth a piece of plastic wrap across the inside of the cookie sheet, making sure it comes up the sides. Don’t use waxed paper or aluminum foil. They’ll stick to the leather and you’ll end up with pieces of foil or paper in your teeth.

Spread a fruit purée on top to a depth of ¼ inch (0.5cm). For each 2 cups of light-colored fruit (such as peaches, apples, or pears), add 2 teaspoons of lemon juice or ⅛ teaspoon of ascorbic acid (vitamin C) to keep the purée from darkening. You can combine different fruits, such as blackberries and peaches, or just stick to one variety.

Place the cookie sheets on the oven racks and follow the general procedures for oven drying discussed earlier. The edges of the leather will dry first, so check for doneness by touching a finger to the middle of the cookie sheet. The fruit leather will be done when it isn’t sticky in the middle, but don’t overdry it. You don’t want it to crack when you try to roll it up.

When the fruit leather is ready, remove the tray from the oven, peel the fruit away from the plastic, and roll it up. After it has cooled, you can re-roll it in plastic for storage. Fruit leather will keep up to a month unrefrigerated or up to 1 year in the freezer.

Drying Herbs in the Oven

Just about any herb you can grow will dry well in the oven. Harvest the herbs when mature but before they’ve begun to flower, as the flowering takes strength from the leaves. The most potent leaves are found at the ends of the stems and they decrease in strength as you get closer to the stem.

Throw away any discolored or dead leaves. Remove the leaves from the stems and place the leaves on a drying rack, allowing space for the air to circulate. Follow the general procedures for oven drying as outlined in the preceding section. Herbs will dry in 2 to 4 hours in the oven.

The microwave isn’t recommended for drying most foods because of their density, but you can use it to dry herbs. One thing to be aware of is that the microwave has a strong tendency to cook the leaves instead of drying them. If you want to try it, place a few stems on a paper towel and cover them with another paper towel. Cook on high for 2 to 3 minutes and then check them. If you’re working with mint, parsley, thyme, or any other tender leaves, check them more frequently and flip them every 30 seconds or so. They’re done when they crumble. If you need to nuke them a bit more, try 15-second intervals so you don’t end up scorching them.

Dehydrators

These appliances are the most popular for drying food—and for good reason. They’re easy to use, take up little space in storage, and produce excellent results. These units are freestanding, electric, have automatic temperature selection, are programmable, and come in a variety of sizes and price ranges. They’re available at hardware stores, retail outlets that sell small appliances, natural food stores, catalogues, and online.

The bigger the dehydrator, the more trays it can hold. Smaller units will have 4 shelves, while the larger models can accommodate up to 12. If your unit has stackable trays, check to see if you have the option of ordering additional trays from the manufacturer.

The unit pictured here has vertical airflow. That means the heating element and fan are in the base of the unit. The one drawback to this arrangement is that foods can drip or fall into the fan vents. This can potentially be a problem if you’re making fruit leather and accidentally dump purée into the heating element and fan. If this does happen, turn off the unit and use a damp cloth to soak up the spill. Be careful not to get water into the heating element.

The other option is a unit with the heating unit and fan built into the side. This creates horizontal airflow. With this design, you don’t have to worry about the spills and all the foods get the same amount of heat and airflow. It might be the better choice, especially if you want to dry different types of foods at the same time or are seriously into making fruit leathers. A dehydrator is more economical to operate than an electric oven, but it’s slightly less economical than gas.

Regardless of what you’re drying, you’ll need to keep tabs on the temperature. It needs to be high enough to cause moisture to evaporate but not so high as to cook the food.

If the temperature is too high at the beginning of the drying process, the outer layer of what you’re drying will develop a hard shell, while moisture will be trapped inside the inner layers with no way out. This is case hardening, as we noted previously, and it’s not good. Success is all about striking a balance and understanding how the process works.

Preheat the dehydrator to 125°F (50°C). Then add the food to the trays and stack them in the dehydrator. After 1 hour or so, when you can see that the exterior of the food has begun to dry, increase the temperature to 140°F (60°C) and hold it there until the food is done. The drying process can take from 4 to 12 hours. Read the instruction book that comes with your dehydrator. It will save you a lot of time and guesswork. It should also include approximate drying times for various foods.

General Procedures

Fruits, vegetables, and meats are all handled differently, but a few basic principles apply to whatever you’re planning on drying. First, start with the best. That means fruits and vegetables should be ripe but not overripe and should be free from bruising and other blemishes. The exception here is fruit leathers, which are an excellent use of bruised or slightly overripe fruit. Fish should be handled gently and as quickly as possible after being reeled in. Meat and poultry products should be lean and fresh.

As with other methods of preserving foods, assemble everything you’ll need before you get started and arrange it in the order in which you’ll use it. You’ll save time and also discover if you’re missing something you were sure you had but turns out you didn’t.

Once you begin the drying process, keep at it until you’re finished. Food that’s only partially dried is a breeding ground for bacteria and molds and can spoil very quickly. If you don’t have time to finish, don’t start until you do.

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