Through the years, people have tried a variety of food preservation methods including salting, smoking, fermenting, pickling, canning, freezing and drying or (our focus in this article) dehydrating. Dehydration works by removing the moisture content from food. This slows down the process of food breakdown from natural enzymes and microorganisms. Bacteria, mold, and yeasts cannot grow in dry environments.
Why Dehydrate Food?
- Dehydrated food is lightweight, portable, and takes up little space;
- Food can be dehydrated without using any energy (though there are methods that do use power);
- Food can be stored without using energy (unlike freezing);
- There are no added ingredients like salt, sugar or vinegar;
- Dehydrated food does not need specialized containers (like cans);
- Dehydrated food is nutrient rich (though the lower the temperature/shorter the time to achieve dehydration the better);
- Dehydrating food is relatively labor saving in comparison to, say, canning;
- You can make healthy snacks;
- You can make packages for instant meals.
There are many ways to gently warm the air and promote good air circulation. Some are simple and a great makeshift way to preserve a small amount of food and some are more complicated and are more dependable for preserving large amounts of food without needing warm, dry weather conditions.
- Electric Dehydrator – Commercial dehydrators are a financial investment but they do offer consistent results and you can buy relatively small ones. They consist of box or cabinet containing a small heating element that warms the air to 90 to 100 degrees, and a fan that ensures good air circulation. If you can mimic these conditions, you can dehydrate food.
- Electric/Gas Oven – It might be a good idea to experiment with your stove before you invest in a commercial dehydrator. You can dehydrate in a regular oven by setting the temperature to 140°F (60°C) propping the oven door open, and blowing a fan across the opening for air circulation. This is a great way to experiment with dehydrating food without investing in a commercial dehydrator.
- Woodstove – You can purchase special racks to hang over or near your wood stove to dry fruits and vegetables. These racks are certainly less of an investment than a commercial dehydrator, but the results may not be as consistent since you will be depending on the heat from the stove and you will have to keep the woodstove fire going until the food is dehydrated. But it does mean you can dehydrate food around the clock without having to pack it up and bring it in at night as you do with outdoor methods we are going to discuss below.
- Outdoor Fire – Even if you do not have a wood stove you can use a fire to dry food (though again you are going to have to keep the fire going all day) and the smoke will keep insects away. String the food for drying over the fire – but not so close that it will scorch. (You should be able to hold your hand at the level of the drying food and feel warmth but not uncomfortable heat.)
- Solar “Oven” or dehydrator – If you live in a sunny climate, you can dehydrate foods in a solar oven which is basically a miniature greenhouse box with clear plastic roof and walls and a dark-colored mesh floor (attracting heat while at the same time creating natural internal airflow without a fan as the hot air moves upward through the dehydrator and also allowing moisture to escape). They are not readily available commercially like the electric models but there are many plans available for free on-line and they are easy to make. The basic premise is that it has a dark-colored backing which traps heat, while at the same time creating internal air currents as the hot air moves upward through the dehydrator. Make sure your fruits and vegetables are sliced extra thin for this method. A really creative way to achieve a solar oven is to use your car, parked in the sun, with the windows slightly cracked to allow moisture out.
- Air Drying – With some foods, or if you live somewhere with low humidity, it may be possible to air dry your food. Air drying is a particularly great way to dry herbs and leafy vegetables like spinach if the weather is not too humid. They need to be tied up in small bundles and hung out of the sun or laid out thinly on a screen. Any other fruit or vegetable can be air dried on racks in the sun. Your main concern is to keep insects off of your food until it is ready to be stored. You will need screens or maybe just thin clothes laid over the drying food.
- Air drying augmented with black tarp – If you have a large black sheet (a tarp or even rubbish bags) that can be spread out on a sunny day you can achieve extra heating and air circulation. Spread out the tarp or trash bags on the ground in full sun, and hang the food low over the tarp to maximize heat. You might need a gauze or mesh cover to keep insects off but you do not want to impede the sun hitting and heating up the black plastic too much.
Preparing Foods For Dehydration
There are some important general points to be made about dehydrating.
Dehydrate good quality fruit and vegetables.
If something has already become unpleasant to eat it is not going to be improved by being dehydrated. The exception is that some fruits that are slightly overripe are no longer appetizing because of their texture and not because they are unsafe to eat and you can go ahead and dehydrate these items because the texture will be changed by dehydration anyway.
Balance temperature and duration for the right degree of retained moisture.
There are three factors you are juggling when you dehydrate food, temperature, duration of the drying process and the amount of moisture left in the food.
Temperature – In order to safely dehydrate food, you need to use a high enough temperature to remove moisture and destroy harmful microorganisms. But dehydrating at too high of a temperature will destroy the flavor, taste, and nutritional value of your food.
- Fruits should be dried at 140 degrees Fahrenheit and will take anywhere from 5 hours to 24 hours, depending on the type of fruit and how thin the pieces are.
- Vegetables can also be dried at 140 degrees Fahrenheit and should take anywhere from 4 to 24 hours.
Duration – You want to properly dehydrate your food by exposing it to the drying process for long enough – but not over-do the process. (The chart below suggests drying duration times for different foods.)
Remaining moisture content – There will still be a small amount of moisture left in your dried food after it is dehydrated, but the key is how much. Leaving too much moisture in the food leaves room for microorganisms to continue to break down the food, leading to faster spoilage.
- Fruits should be dried to about 20% moisture content. They should not be at all damp or sticky but they can still be fairly soft to the touch. Berries should be dried out enough to make a small rattling sound when shaken.
- Vegetables should be dried to 10% moisture content. They should be crisp and capable of being snapped.
Lean meats, fruits, legumes, and vegetables are great for dehydrating. Avoid dehydrating foods that are high in fat which can easily go rancid or just not dehydrate properly.
Steps To Dehydrate: (The extra step needed for fruit dehydration is described in the next section.)
- Wash the food. Cut out blemishes or soft spots. Remove seeds and cores, where relevant.
- Slice up the food. The thinner you slice your fruits and vegetables, the more quickly they will dehydrate and the better your results will be.
- Blanch your vegetables. This is the process of boiling foods then cooling them in cold water. Blanching helps preserve the taste and texture. Most foods only need to be boiled for a few minutes and some only need to be dipped briefly in boiling water. One of the easiest ways to achieve this is to put the food you are blanching into the kind of loose-weave sack that a pocket of potatoes or orange often come in. You can then hold the top of the sack, bounce it up and down in the boiling water to make sure all parts of your food is being exposed to it, and lift it out in one mass. (For blanching times, see the chart below.) Note: Most foods that you can eat raw do not need to be blanched before you dehydrate them. For example, apples or tomatoes can be dehydrated without cooking.
- Leave the veggies in the cold water until they are cool. Spread them out in a single layer on a pan or tray.
- Put your food in whatever form of dehydrating equipment you are using.
- Check periodically, and stir the drying food around a bit.
Blanching and drying times:
- The drying times given below are assuming using the oven method at a temperature of 200°F. You will have to experiment with the times for other methods.
- The drying times will vary widely on how thinly the food is sliced or, with cabbage, for example, how thick the leaves are.
*Thinly slice to somewhere between 1/8″ and 1/4″ thick. 1/8″ and you end up with paper-like chips. 1/4″ is a bit too thick.
Herbs are extremely easy to dehydrate and can provide you with spices and teas for your food storage.
Many herbs can simply be hung to dry in quite small bundles – so that all the leaves are exposed to air. (Herbs with tiny leaves, like thyme, can be hung inside a loose-fitting cloth or paper bag to catch leaves falling off as they dry.) You can of course use a dehydrator or oven if you want to achieve dehydrated herbs quickly or you are living in a humid or dusty environment.
Treat Fruits to Prevent Discoloration
Some fruits, like apples and bananas, will turn brown during the dehydration process and need to be pre-treated if you want to keep the color and flavor. You can soak fruit for three to five minutes in a solution of ascorbic acid and water or simply dip them in a mixture of lemon juice and water for no more than a minute before putting them on the tray. This process is known as “dipping” and is labeled “dip” in the chart below
Food dehydrates best in small pieces with a large surface area. High water fruits should be sliced as thinly as possible and separated so that there’s good airflow on all sides.
Raspberries, Blueberries, & Blackberries
Small berries are probably the easiest thing to dehydrate as they do not need any special preparation before you start dehydrating them. They make tasty additions to cereal, granola, and trail mixes. Sealed berries, like blueberries, will dehydrate best if their skin is punctured to allow moisture to escape. A good way to do this is by quickly blanching the berries in boiling water for 30 seconds to pop them, and then shocking them by placing them in cold water. This pops the berries open and has the added benefit of sterilizing the outside of the berries, which helps prevent spoilage while they are drying.
You can also experiment with fruit leathers. All you need is fruit puree spread in a thin layer on a dehydrator tray. When it’s dry, slice it into strips and roll it up with wax paper. Great combinations include applesauce and blackberries, strawberries and bananas, and peaches and raspberries.
Storage After Dehydration
Dehydrated food is some of the easiest food to store long term. It requires no electricity. It takes up a relatively little space.
Here are a few simple pointers for the storage of your dehydrated food.
- Make sure the food is completely cooled before you pack it. It could otherwise sweat and re-introduce the possibility of moisture and contamination.
- Adapt any sort of air-tight container for the storage – Tupperware, canning jars, freezer bags, etc. (Clear containers are excellent for beginners because they allow you to keep an eye on your food until you are confident you have mastered your dehydration.) Solid containers, rather than bags, are desirable for keeping more delicate foods that can be crushed or powdered easily.
- Keep the filled containers in a cool, dark place like a cabinet or cellar.
- Check stored dehydrated foods periodically. If you notice moisture inside a container, remove your food and re-dry and repackage it. Throw away any food with signs of spoilage like mold or an odd smell should be discarded.
- The National Center for Home Food Preservation says that dehydrated fruit can be stored for up to a year at 60°. Vegetables can be stored for about 6 months. Many foods will keep for much longer under proper conditions.
An Example Of A Home-made Solar Dehydrator
Dehydrator raised off ground to allow air circulation
Cutting Up Vegetables
Vegetables placed in string bags for easy ‘dunking’.
Vegetables In Dehydrator
For thousands of years, one of humanity’s greatest challenges has been preserving food during times of plenty to see them through the times of scarcity. Are you up to the challenge as well?