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An Introduction to the Drying Food Preservation Method


Dried strawberries photo by Carole Cancler
Drying is the simple process of dehydrating foods until there is not enough moisture to support microbial activity. Drying removes the water needed by bacteria, yeasts, and molds need to grow. If adequately dried and properly stored, dehydrated foods are shelf stable (safe for storage at room temperature). The drying food preservation method is easy to do, very safe, and can be used for most types of foods (meats, fruits, and vegetables).

There are several methods for drying foods. Two of the easiest and most common that can be used in any climate are oven drying and drying with an electric dehydrator appliance; these methods are described below. The other methods are air drying (in the shade during warm weather), sun drying (limited to desert climates), solar drying (requires specially built dryer), and pit oven drying (useful when other methods are impractical). Find these other food drying methods describe in The Home Preserving Bible by Carole Cancler.

How to dry food in a conventional oven

Oven drying is a good choice if you have never dried foods before, or plan to do only occasional drying. It tends to be slower than an electric dehydrator, but there is little or no investment in equipment and you don’t have to depend on the weather as with other methods.

Foods that are well-suited to oven drying are meats; seafood; fruit leather; low-moisture foods such as herbs, potatoes, bread cubes, berries, and meaty tomatoes (roma or paste-type); and excess produce you might otherwise throw out, such as onions, celery, and bananas. If you are new to drying, start with a few of the easiest foods to dry: berries, banana slices, tomato slices, chopped onions, oven jerky, and smoked salmon.

Here are the basic steps for oven drying foods:

  1. Prepare suitable trays for drying foods (see information below).
  2. Prepare food for drying. Preparation methods vary depending on the food you want to dry. For fruits and vegetables, you wash and then usually halve, quarter, or slice the produce. For light colored fruits and all vegetables, you also steam-blanch to deactivate enzymes or prevent browning in light colored foods, and then pat dry. Find more detailed instructions in this article: Methods for dried fruits, dried vegetables, and dried tomatoes. Meat or fish jerky is often marinated and may also be cooked before drying. Find more information in this article: How to decide whether to precook meat when making dried beef jerky. For more detailed instructions on preparing different types of foods for drying, see The Home Preserving Bible by Carole Cancler.
  3. Preheat (a gas or electric) oven to the lowest temperature setting. Maintain an oven temperature between 125°F and 145°F. Check the oven temperature with an accurate thermometer.
  4. Decrease the temperature by propping open the oven door with a wooden spoon or folded towel. Caution: the oven-drying method is not safe in a home with small children.
  5. Maximize air circulation to speed drying. Place a fan on a chair near the propped-open oven door so that it blows away the hot, escaping air. Open nearby doors and windows to promote more airflow.
  6. Dry until pliable or crisp: The extent of dryness is somewhat a matter of preference (see How to Use Dried Foods below). Therefore, the length of drying time can fluctuate widely (from a few hours to more than 24). Drying time also depends on several factors: the type of food (meat, fruit, vegetables, etc.), the size of the portions to be dried (thick or thin), the drying method used (sun, air, oven), and the weather (especially humidity, which greatly increases drying time).
  7. Tips for successful drying include drying foods only on days when the humidity is not high, space the food about an inch apart, and fill only half of the oven racks with food.

Suitable Trays for Oven-Drying Foods

Trays used for drying foods in an oven (or other methods than a food dehydrator) need to be of a food-safe screen material such as plastic (preferably polypropylene), stainless steel, Teflon or Teflon coated fiberglass, or wood. An economical solution is to stretch cheesecloth or natural muslin over an oven or cake rack or a wood frame, and attach it with masking tape, paper clips, or clothespins. For a more permanent, but more costly option, have (window) screens made at a hardware store and use them for drying.

Avoid materials which can leach harmful chemicals, darken the food, or melt at drying temperatures. These materials include:

  • Do not use uncoated fiberglass and vinyl.
  • Do not use metals other than stainless steel (such as aluminum, galvanized steel, and copper); they can transfer a metallic flavor to food, rendering it inedible. Covering metal with cheesecloth or muslin is another option, especially if you are re-purposing material and are unsure of the type of metal.
  • Do not use green wood, pine, cedar, oak, and redwood.

After oven drying a few foods, if you want to continue to use the drying method, consider investing in an electric food dehydrator.

About electric food dehydrator appliances

A food-dehydrating appliance has few weather dependencies, can consistently produce a quality product, and is less prone to inconsistency or other problems when drying foods. This makes it easier than most other methods.

A good food dehydrator provides variable temperature control and good air circulation. A temperature control with a range of 85°F to 180°F provides full flexibility for drying all types of foods, from delicate herbs and firm fruits to meat jerkies. A temperature control with a maximum of 160°F will limit your ability to dry meats and fish.

You can purchase a basic food dehydrator model for under $100, which is a good choice for first-time users or those who want to dry foods occasionally and in small amounts. Basic models have limited temperature ranges, vertical airflow, single-wall construction, and limited drying capacities.

More deluxe food dehydrator models cost $200 or more, and offer more temperature range, efficient horizontal airflow, double-wall construction, and larger drying capacities.

With a food dehydrator, you simply prepare the food and place it on the appliance trays, preheat the dehydrator to 125°F to 135°F, and the appliance does the rest.

How to use dried foods

You can used dried foods in a variety of ways:

  • eat dried foods as is (such as snacking on dried beef jerky and dried fruits)
  • rehydrate dried foods water (such as adding vegetables to a meat stew)
  • grind dried foods into a powder (for example, grind tomatoes to a powder that you can reconstitute with water to make tomato sauce).

Therefore, you may dry foods until pliable, especially if you want to use them as a snack food. If you want to store dried food longer or use it to grind to a powder (such as tomatoes to make sauce), then you want them to be crisp and brittle. Less-dry products have considerably shorter shelf life—from 2 weeks to 2 months. Very dry foods, if properly stored, may last several months.

Whether pliable or crisp, condition all foods at the end of the drying process. Alternatively, you may store partially dried or unconditioned foods in the freezer.

How to condition and store foods after drying

Individual pieces of food dry at different rates; some pieces will have more moisture than others. If there is too much moisture left in a few pieces, they can grow mold and contaminate the entire batch. To guard against mold growth, you need to condition dried foods before you store them. During conditioning, the moisture will equalize—that is, excess moisture will transfer to drier pieces, until it is evenly distributed throughout the batch.

To condition dried foods, place them in a tightly closed container at room temperature. Stir or shake the contents every day for a week. If you open the container to stir the contents, be sure to close it again tightly. During conditioning, if moisture forms on the inside of the container, the food is not sufficiently dry and you need to return it to the dryer.

To store dried foods after conditioning, seal dried food in airtight containers that hold only enough food to be used at one time. This reduces the number of times a package is reopened. You can also limit air by taping over jar enclosures or using a desiccant to absorb oxygen. Ideally, you want to store dried foods at a constant temperature between 40°F and 70°F. Be sure to store foods in a closed cupboard or dark room, away from light. If you live in a dry climate, your dehydrated foods will tend to stay fresh longer. However, if you live in a humid area, moisture can get in and shorten storage life considerably. In high-humidity locations, put dried food in zipper-lock plastic bags that allow you to push out excess air.

You can store properly packaged, well-dried foods at room temperature for up to 1 year. Less dry, pliable products have a shelf life of a few weeks to several months. Storage life decreases with packaging that is not airtight, reopening packages, and fluctuating temperatures. You can vacuum-seal, refrigerate, or freeze any dried food for longer storage.

Check dried foods monthly for spoilage—usually mold. Use dried foods before other types of preserved foods, such as frozen or canned. Most importantly, enjoy eating your dried foods and be sure to experiment with different ways of using your stored treasures.

Hints for successfully storing dried foods

  • Always store dried foods in airtight containers in a cool, dry place.
  • Reduce the number of times a package is reopened by using containers that hold only enough food to be used at one time.
  • Limit air, light, and heat. Put masking tape over jar enclosures or use a food-safe desiccant in the jar to absorb excess oxygen. Be sure to store foods in a closed cupboard or dark room, away from light. Ideally, you want to store dried foods at a constant temperature between 40°F and 70°F.
  • In humid locations, put dried food in zipper-lock plastic bags that allow you to push out excess air. This helps to prevent moisture from re-entering the food, shortening the storage life considerably.
  • To increase storage life, vacuum-seal, refrigerate, or freeze dried foods.
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