What is dehydration? Dehydration and human culture

Dehydration is an age-old method of food preservation by removing water through evaporation. In ancient times, the sun was the means to draw out and evaporate moisture. Primitive people sun-dried a variety of food such as berries, grasses, roots and meats. For example, fishing cultures such as Phoenicians and Mediterranean fishermen laid their catches out to dry, the Chinese sun-dried tea leaves, the Essenes would soak and sprout wheat before drying it. In the contemporary age however, a purpose-built electric equipment called dehydrator is used. The dehydrator offers greater control over temperature.

Why dehydrate your foods?

Maximal nutrition
Compared to other methods of preservation such as canning that involves heat, dehydration preserves majority of the nutrients and original color. When exposed to heat, nutrients and enzymes deteriorate. The recommended temperature range to dry food is 95°F/35°C to 105°F/41°C.

Lightweight and portable food supplies with minimal storage space
Dehydration whittles food down to smithereens, so a pound of tomatoes can easily fit into a small package. For example, the military and many camping enthusiasts embrace dehydrated food because of the ease of transport and space efficiency. If you are an apartment dweller or suffer limited storage space, dehydration is also a great space-saver.

Little skill and time required
Slice, spread, dry, store. Dehydrating food is as simple as it sounds. Unlike canning, you do not have to worry about spend a lot of time creating water baths, sterilising equipment and watching over the temperature. Many have expressed exasperation at failed moldy canning, but it is less common with dehydrated foods. Even if you are working full-time, you can let your dehydrator run while you are out without any mishaps happening.

A creative, flavorful and clean “cuisine”
Condensed morsels of flavor bombs, a phrase that succinctly describes dehydrated food. When you dehydrate food, fruit especially, their flavors become concentrated and sweeter. In addition, the texture changes to leathery or crispy depending on sugar content. The array of tastes and texture of dehydrated foods add interest to dinner preparations and stimulates the palate. Also, the dehydrator itself can be utilized as a food warmer, to gently reheat foods such as raw vegetable spaghetti, raviolis and soups. Preparing your own dehydrated foods means you know exactly what goes into them and no chemical agents such as sulphur dioxide are added.

Choosing a dehydrator

When purchasing a dehydrator for home use, consider these five main factors: fan arrangement and airflow; dehydration capacity; degree of access and control; temperature and timer controls; material and price. Below I explain each factor in more detail.

Fan arrangement and airflow: horizontal and vertical airflow units
Horizontal airflow units have the fan situated at the back and work similar to electric ovens, blowing hot air through foods on each tray. Heat is evenly distributed between the trays without the need for frequent rotation. They tend to dry foods more efficiently and as such, retain more vitamins. In addition, flavors of various foods are less likely to get muddled up so you will be able to dehydrate different foods simultaneously.

Vertical airflow units have the fan on the bottom, or less commonly top, and distribute heat upwards through each tray as hot air rises. Food is dried less evenly with lower trays typically drying faster than upper trays. Frequent rotation is required to counter this shortfall. In addition, it is more difficult to clean as drippings from fruits and vegetables can occasionally get onto the fan.

Dehydration capacity
How much food you will be drying? Horizontal airflow models are limited by the fixed number of shelving units – typically five or nine trays. There is no way to increase drying space once you have maxed out its capacity. The benefit is you can leave out a tray to create extra room for drying thicker foods or warm small jars in the dehydrator.

Vertical airflow models are versatile in that the stackable trays can be further expanded upon by simply adding more trays (to efficiency limit). The downside is that you may not dehydrate thick cut foods, and the center hole may be inconvenient for projects that involve spreading a semi-liquid on the tray, such as making fruit leather.

Degree of access and control
Horizontal shelving models are by far more user-friendly as specific trays can pulled in and out easily like drawers. In contrast, for vertical stacking models, you would have to remove the top trays before accessing produce at the bottom layers. This is not only cumbersome but will prolong dehydration time due to fluctuation of temperature and humidity.

It is also desirable to have control over temperature and time. Higher end models come with a thermostat to set specific temperatures for dehydration and a timer that automatically turns off so you would not have to guard over the food like a hawk.

Material – plastic or stainless steel
Dehydrators can be made of plastic or stainless steel. Plastics include the standard food-grade plastics and BPA-free (bisphenol A) plastics. For example, the popular brand Excalibur uses polycarbonate for the case and BPA-free polypropylene for the mesh screens. There is concern over the safety of polycarbonate plastic dehydrator units that it may leach toxic BPA, a known endocrine disruptor. However this only occurs significantly at much higher temperatures of above 212°F/100°C, beyond the temperature range for dehydration of most foods. If you are uncomfortable with using plastic dehydrators, the safer option is stainless steel units, available with the brands Excalibur and Weston.

Horizontal shelving models usually come with more features, are more sturdy and can sustain heavy-duty use. Although pricier by a few hundred dollars, it is worth to invest in an appliance that can last for several decades. Top-rated brands for horizontal shelf-type dehydrators are Excalibur, Sedona, Weston Supply and L’Equip. However, if you are on a tight budget, vertical stacked dehydrators are an affordable option. A popular brand is Nesco.

Whatever your choice, remember to select a machine that comes with a manufacturer’s warranty to ensure that you are covered should you ever encounter a problem with your food dehydrator.

Alternatives to electric dehydration
Other methods of drying are solar dehydrating, oven dehydrating and hang-drying. These will not be covered here.

Handy supplementary equipment

Sharp knives, mandoline or a food processor with slicing discs is helpful for slicing food evenly of a specific thickness, such as for vegetable or fruit chips. An egg slicer works for soft foods like mushrooms and strawberries. Paraflexx sheets are required for drying runny or liquid spreads that would otherwise drip through the plastic mesh sheets.

Food preparation for dehydration

Plan ahead to dehydrate foods on the same day as you bought the produce. Foods will be at their freshest, and this is the best time to lock in flavor, color and nutrition.

Select the best fruits and vegetables; they should be brightly hued and heavy. No rotten spots or mold as these are not something you want to preserve!

Pretreatment: pitting, blanching, acid treatment and slicing as applicable for the produce
Remove pits, stems and peels as these can become bitter and tough when dehydrated. Blanch or steam fibrous vegetables and fruits with a tough skin such as grapes, cherries and plums. The benefits of blanching are that the dehydrated form is softer and rehydrates faster although some enzymes will be destroyed inevitably.

Fruits that are prone to oxidation such as bananas, peaches, apples and potatoes benefit from a dip in citrus juice of lemon or orange to protect their color and nutrients. The juice coating lends a touch of flavor to the final product; I find the most neutral to be orange juice. A word of caution is to avoid acidic juices on green foods such as broccoli and herbs. The acid will alter the chlorophyll and you will end up with repugnant brownish-gray food.

When it comes to slicing, it pays to be perfectionist and achieve uniform slices so the food pieces will be dry at the same rate. Cuts usually range from 1/8-inch to 1/2-inch thickness. As a general guide, the higher the food’s water content, the thicker the cut you should start with. Distribute vegetable and fruit slices in a single layer and avoid overlapping. Different kinds of vegetables and fruits may be dried simultaneously but strong smelling vegetables like onions should be dried separately.

Using your dehydrator for living foods

Potential products from your dehydrator

  • Dehydrated fruit slices of various types of fruits
  • Dehydrated vegetables eaten as snacks or used in cooking
  • Fruit and vegetable leather made from purees and formed into strips
  • Powdered mix made by grinding down dried fruits and vegetables to be used in preparation of food products such as soups or garnishes

Setting the temperature
The goal of using your dehydrator is to dry food at a low temperature that preserves the enzymes rather than cook the food, yet high enough to remove moisture quickly to avoid bacteria growth and spoilage. How do we set this optimum temperature? First, it is important to understand the difference between air temperature and food temperature. The food temperature is about 20ºF/11ºC cooler than air temperature because as moisture evaporates from the surface of the food, it cools it. Notably, stated on the Excalibur website is that the temperature on the thermostat refers to the food temperature.

With this knowledge we can apply the two-temperature fast dry method optimal and timely dehydration. First, set the temperature to a high of 145ºF/64ºC for the first two hours of dehydrating. The food temperature will not exceed 118°F/48°C – the recognised standard temperature for living foods – due to high moisture content. After two hours, turn the temperature dial to about 105ºF/41ºC and keep it at this temperature until the food is finished. This will significantly reduce the drying time by several hours while still ensuring that you are making raw and living foods.

Test for doneness
Vegetables and fruits are sufficiently dried when they are crisp and brittle or pliable and leathery, depending on type and form (see below). A quick trick to test if the food is dry enough is to put the cooled dried food in a clear plastic bag. If beads of moisture form on the inside of the bag, your food is not ready and you need to continue drying it. No droplets means you can safely store it.

Times and textural outcomes for different fruits and vegetables

Textural OutcomeIngredientDescription
Crisp and brittle fruitsapple, banana, citrus fruitsfood breaks when bent
Crisp and brittle vegetablesbroccoli, cabbage, corn, garlic, green beans, green leaves, peas, radishes, tomatoes, zucchinifood breaks when bent
Pliable and leathery fruitsberries, dates, grapes, kiwi, pineapples, mangoes, melons, papaya, pears, stone fruits, strawberriesfood looks shriveled and bends but does not crack. Fruits may be tacky but should not stick together
Pliable and leathery vegetablesbeets, carrot, celery, cucumber, eggplant, mushrooms, okra, onions, peppers, pumpkinfood looks shriveled and bends but does not crack

Storing dehydrated food

Allow the food to cool completely to room temperature before storing it in airtight conditions in suitably sized glass jars, zip-lock or vacuum bags. For optimal protection of flavor and color, fill the container with rice or add an oxygen-absorber sachet. They come in three sizes: 100cc, 300cc and 500cc. CC refers to the volume of oxygen absorbed; use stronger oxygen packs for larger jars. It will definitely be an added bonus to use a vacuum sealing machine for ultimate preservation. Finally, label the container with its contents and date of preparation. It is worth to take time and make the labels artistic!

Store the individual containers of dried food in a cool, dark and dry environment with a consistent temperature such as the pantry or freezer. Avoid storage in the refrigerator as the excess ambient moisture and temperature swings can cause moisture build-up and spoilage. Foods that are completely dried and well-stored stay good for a year.

Rehydrating dried foods

Dried fruits and vegetables and be eaten as it is or reconstituted using one of the methods below.

At room temperature or cool liquid, soak the food for two hours or more, using two cups water for every one cup dried fruit or vegetable. Instead of water, try juice or non-dairy milk, depending on the recipe. Unblanched vegetables will take longer to rehydrate.

Steep the food in fresh boiled water for 15 minutes.

Steaming or cooking
Steam for five minutes or use it in a recipe in its dried form. Vegetables are better pre-soaked before adding them to a recipe. One cup dried vegetables equals about three cups fresh.

Additional tips
Avoid adding salt as this can slow the rehydrating process based on science of osmosis.
Avoid adding sugar as during drying, starch turns to sugar and sugars become concentrated.
Soaking liquid may be reserved for other purposes.

Cleaning your dehydrator

From experience, the Excalibur dehydrator has been convenient to maintain. The outer case, door, trays and paraflexx sheets can be easily cleaned by wiping with a damp cloth and warm soapy water. The tray mesh requires a bit more work as food pieces tend to get stuck in the ridges. To remove the grits, I use a vegetable brush or unwanted toothbrush and warm soapy water and then let them air-dry.

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