Food dehydrating, also called food drying, is a food preservation process which removes water from food. The water content of food is generally very high, usually between 80% to 95% for various fruits and vegetables and 50% to 75% for different meats. Removing moisture from food inhibits various bacteria, yeasts and molds from growing and spoiling the food, thus, food dehydrating is an ideal process for the preservation and storing of food.

How does food dehydration work?

Successful food dehydration is dependent on two basic elements; heat and air. Food dehydration requires the application of constant temperatures that are hot enough to remove moisture and dry food but not hot enough to cook food. Ideal drying temperatures are usually between 115 degrees to 140 degrees Fahrenheit, or 46 to 60 degrees Celsius. Food dehydration also requires air flow and circulation to remove the moisture that is released into the air during the dehydrating process. Ideally, warm, moist air will be replaced with dry cooler air aiding in the food drying process.

How does a food dehydrator work?

A food dehydrator uses the same two dehydration principles; heat and air. A typical food dehydrator contains an electric component for heat and a fan and air vents for circulation. A food dehydrator’s heating component and fan work in concert to remove moisture from food. As the heat warms the food, its moisture is released and evaporated into the air. To achieve dehydration, that humid, moist air must be removed and replaced with dry air via the food dehydrator’s fan and vents. The faster the air current and the better the ventilation, the faster and better food will be dehydrated.

What food dehydrator product features are important?

• Total Drying Area – How much space, or total drying area, does the food dehydrator have to dry food? A food dehydrator’s total drying area is typically expressed in square feet.

• Air Flow – Food dehydrators remove moisture from food via heat and air flows. Food dehydrator air flows are designed either horizontally or vertically. Horizontal air flow food dehydrators have their heating element and fan located on one side of the dehydrator. The drying trays that hold the food are arranged like drawers inside the food dehydrator. Vertical air flow food dehydrators have their heating element and fan located at the base of the dehydrator. The drying trays that hold the food are stacked on top of the base.

• Thermostat – A thermostat is a device used to regulate the temperature of a heating or cooling system so that the system’s temperature is maintained near a desired, chosen amount. A thermostat does this by switching heating or cooling systems on or off, as needed, to maintain the desired temperature.

• Watts – The energy consumed or used by a food dehydrator is measured in watts, similar to that of the light bulb. The watt power of a food dehydrator should be considered in relation to the total drying area. More drying trays and larger dehydrator dimensions should require more watts used by the dehydrator to ensure adequate dehydration.

• Price – A good metric to compare different dehydrators that vary in size, total drying area, wattage and or price is to compare their cost per square foot of total drying area. To calculate, divide a food dehydrator’s cost by that unit’s total drying area.

What foods can be dehydrated?

Fresh fruits, vegetables, meats, fish, breads and herbs are the foods that are typically dried. In fact, you can dry most items that have high water content.

What are the benefits of food dehydrating?

• Dried food is shelf stable, naturally preserved and can be stored in air tight containers for up to one year.

• Dried food is very lightweight and thus easy to store, carry and consume as needed.

• Dried food fits the portability and nutritional needs of campers, outdoors enthusiasts and outdoor sportsmen and women.

• Dried fruits and dried vegetables are good sources of vitamins, minerals, fiber, antioxidants and natural carbohydrates (primarily the food’s natural sugar).

• Dehydrated meat, also known as jerky, is low fat, tasty and full of protein.

• Food drying can be an important part of the growing local food movement. Food dehydrating will allow you to reap year round rewards of your home grown garden and or locally and regionally grown produce. Don’t give away your extra produce, dry it, store it and enjoy it year round.

• A food dehydrator can be an important part of a raw food lifestyle. Raw foodists eat primarily uncooked, non-processed, organic foods and foods dehydrated at 115 to 120 degrees Fahrenheit (46 to 49 degrees Celsius).

• Dehydrated food can serve as an emergency food supply. The U.S. Department of Homeland Security recommends at least a three day supply of non-perishable food as part of an emergency supply kit.

Is food dehydrating difficult?

No, food drying is not difficult. The basic steps in dehydrating food involves selecting food at its peak flavor or ripeness, thoroughly washing the food, cutting the food into 1/8 to 1/4 inch rings or slices and then drying the food at a constant temperature.

What kitchen appliances or items are needed to dehydrate food?

Items that are indispensable include a sharp knife or knives for slicing and a food dehydrator or an oven for food drying. Other useful items can include a blender, food processor, steamer, strainer and saucepans. Nice to have, but not necessary, are more specialized utensils including a parer, slicer, corer or pitter for removing skins, pits and cores from fruits and vegetables.

Does drying affect the nutritional value of foods?

Food dehydrating does cause some nutrition loss with vitamin C in foods being primarily impacted. Vitamin C is a water soluble vitamin and thus can be impacted by the dehydrating process. However, applying a coat of lemon, lime, pineapple or other citrus fruit juice to food before the dehydrating process can add vitamin C, help prevent food discoloration add flavor and offset nutrition loss.

Is dried food safe to eat?

Yes, properly dehydrated food can be stored in air tight containers and used and consumed for up to one year. Food dehydrating is the process of removing a food’s water content and moisture. Moisture is the enemy of preserved, shelf stable food. Removing moisture from food inhibits various bacteria, yeasts and molds from growing and spoiling the food, thus, food dehydrating is an ideal process for the preservation, storing and consuming of dried food.

As it relates to dried meat or jerky, the United States Department of Agriculture (USDA) currently recommends that before making jerky (dehydrating meat at temperatures of 130 to 140 degrees Fahrenheit or 54 to 60 degrees Celsius), the meat’s internal temperature be raised to 160 degrees Fahrenheit or 71 degrees Celsius. The USDA recommends this step to safely ensure that any harmful microorganisms (E. coli, etc.), that may be present in meat, be destroyed prior to the dehydrating process.

What is jerky?

Jerky is meat that has been dehydrated or dried through low heat. Making jerky from meat is a food preservation technique that substantially removes the meat’s moisture and inhibits enzyme and bacterial growth that would otherwise spoil the meat. Jerky has been made for hundreds and thousands of years. The word jerky derives from the Quechua word charqui. Quechua is a South American language that predates the beginnings of the Inca civilization in the 1200’s.

Is it necessary to pretreat foods before drying them?

Pretreatment is not necessary for successful food drying, but it can enhance the color, flavor, and texture of certain foods and restore vitamin C to fruit that may otherwise be reduced in the dehydrating process. Pretreatment methods include dipping and or sulfuring fruit, blanching vegetables and marinating meats.

Fruit dipping is a pretreatment used to prevent fruits from turning brown and to add vitamin C to fruit. Ascorbic acid and fruit juices high in vitamin C (for example lemon, orange and pineapple) may be used for dipping. Sodium sulfite is a water soluble compound of sodium and can be used as a dipping preservative to prevent dried fruit from discoloring or browning.

Blanching is briefly precooking vegetables in boiling water or steam and it is used to shorten food drying time and kill organisms that could cause spoilage. Steaming is the preferred method as it is not nearly as damaging to the vegetables from a nutritional loss standpoint.

Prior to dehydrating meat, the United States Department of Agriculture (USDA) currently recommends heating meat’s internal temperature to 160 degrees Fahrenheit, or 71 degrees Celsius, in order to kill any harmful organisms (e. coli, etc.) that may be present. Prior to dehydrating, heating meat in a marinade imparts flavor and texture to the meat.

How long does it take to dehydrate food?

Drying times can vary from several hours up to twenty four hours. The drying times required to properly dehydrate various food depends on several factors including:

• The Type of Food and the Amount of Food – The type and amount of food being dehydrated will obviously influence how long it takes to dry.

• The Foods’ Water Content – Water content is the percentage of a food’s weight that is comprised of water. The water content of fruits and vegetables are typically 80% to 95%. The higher the water content of the food being dehydrated, the longer the drying time.

• The Thickness or Thinness of the Food Slices – The thinner the slice of the food being dried, the quicker the drying time.

• The Dehydrating Temperature – The lower the temperature that food is dehydrated at, the longer the drying time. Typical temperatures for dehydrating fruits, vegetables and nuts, are between 115-120 degrees Fahrenheit (46 to 49 degrees Celsius). This range of temperatures achieves the best dehydrated food product, avoids case hardening and helps preserve enzymes and nutrients within the food.

• The Amount of Air Circulation – The more there is, the shorter the drying time will be.

• The Relative Humidity – The higher the ambient humidity, that is the more moisture in the air, the longer the drying time.

• Personal Taste – Do you want your dehydrated food softer and more pliable or more crispy and crunchy? Crispy and crunchy requires more dehydration time.

What are the proper dehydrating temperatures?

The three main categories of food that are typically dehydrated require different drying temperatures:

Meats and Fish: 130 degrees to 140 degrees Fahrenheit and above

Fruits and Vegetables: 115 degrees to 130 degrees Fahrenheit

Herbs and flowers: 100 degrees to 110 degrees Fahrenheit

What is raw foodism or a raw food lifestyle?

Raw foodists eat primarily uncooked, non-processed, and organic foods. Generally speaking, if 75% to 100% of a person's total food consumption is raw food, then he or she is considered a raw foodist. Raw plant foods are generally defined as foods that have not been heated above 115 degrees Fahrenheit. Raw foodists believe that foods heated above this temperature lose much of their nutritional value and natural enzymes and are harmful to a person’s body.

Will food flavors mix and combine if I dry different foods at the same time?

It is best to dehydrate like foods at the same time, fruits with fruits, vegetables with vegetables, etc. It is probably not advisable to dehydrate onions or asparagus along with pears or bananas.

How do you know when foods are properly dried?

The best way of deciding if food is dry is to feel it. In general, fruit will feel soft, pliable and leathery. Vegetables will feel more crisp and brittle. Dried meat, or jerky, should be flexible and not brittle. Jerky is done when a test piece cracks on the edges but does not break when it is bent. It is best to let food cool before testing it for dryness. Lastly, it is better to slightly over dry versus under dry food to make sure that its moisture is removed.

How do you store dried foods?

Moisture, including relative humidity in the air, is the enemy of dried foods. Store dried foods in airtight containers in dry, dark places that have a moderate ambient temperature.

Can I dry food in a home oven?

Yes, a home oven can be used as a makeshift food dehydrator. Food dehydration essentially requires two basic elements; heat and air flow. These two elements work in concert to remove moisture from food. As the heat warms the food, its moisture is released and evaporated into the air. To dehydrate food in an oven, you simply place food items on the wire racks in your oven, set the heat and leave the oven door slightly ajar to let air and moisture out.

However, dehydrating with an oven does have its disadvantages including: a) an oven lacks air movement which is a critical component of food dehydration and moisture removal, which could result in improperly dehydrated food, bacteria and microbial growth and premature food spoilage, b) inefficient energy use given the oven’s size and cost (it is estimated that leaving the oven door open will require the oven to work 25% to 30% harder to maintain the desired oven temperature), c) the danger inherent in leaving the oven door open while it is in use, especially if you have younger children, d) the heat emanating from the open oven door will heat the surrounding area – not so good if it is spring or summer or if you live in a warmer climate.

Can I dry food in a microwave oven?

It is not recommended for most foods. Microwaves are built for cooking and thawing food quickly using various levels of electric power that are converted to very short radio waves that in turn heat the food. It is difficult to control a microwave oven’s temperature and thus difficult to maintain the constant level of heat that is required for proper food dehydration. Further, microwaves do not have air flow.

Published 5/18/2009 12:00:00 AM

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