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Terms when Drying Foods

Home food preservation terms can be confusing and very scientific. Read about the meaning of important drying terms.

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Updated:

May 3, 2024

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One of the easiest ways to preserve foods is to dry them. Food drying has been happening historically since the time of the Egyptians. Dried food is lightweight, portable, and shelf-stable. Fruits, vegetables, herbs, and meat can be dried into safe food products. To make safe products, we need to learn how to dry foods correctly, and there are some terms that are important to understand for drying.

Drying Terms Defined

When we dry foods, we are trying to remove moisture or water from food so bacteria, yeast, and mold cannot grow and spoil the food.

Enzymes are substances in foods that promote a chemical reaction. In fruits and vegetables, enzymes are important for the ripening process. When we dry foods, we slow enzymatic reactions from happening, but we do not inactivate the enzymes.
Pretreatment. Fruits and vegetables are pre-treated before drying to help slow such enzymatic reactions. Fruits are pre-treated before drying to prevent darkening during the drying process when exposed to air and to preserve flavor and nutrients. Examples of pretreatments for home-dried products are ascorbic acid, ascorbic acid mixtures, honey dip, fruit juice dip, and steam blanching. See Let's Preserve: Drying Fruits and Vegetables (Dehydration) for detailed instructions on each of these pre-treatment methods.
Blanching. Vegetables are treated using steam or water blanching prior to drying and freezing. Blanching is the process of scalding produce either in boiling water (i.e., water blanching) or above steam (i.e., steam blanching) for a specified amount of time. After blanching, the produce is put into ice water till cooled to the touch to stop the cooking process. Blanching is an important pre-treatment step because it stops quality deterioration over time. For detailed information on designated times vegetables should be blanched before drying please consult the National Center for Home Food Preservation Colorado State Drying Vegetables Fact Sheet.

Judging Dryness of Foods

Fruits are considered dried when the moisture content is < 20% and the fruit is not tacky to the touch but is still pliable. This can be assessed by cutting a piece of fruit in half making sure you cannot squeeze out any moisture and the fruit is not sticky. After fruits are dry, they must be cooled for 30-60 minutes before packaging. Quickly package the fruit so moisture does not re-enter the fruit.

Conditioning. Fruit must be conditioned to make sure the 20% moisture is distributed evenly throughout the fruit piece. Conditioning is achieved by shaking the package of fruit for the first 7-10 days and looking for any signs of visible moisture.
Vegetables are dry when they are brittle at 10% moisture. Vegetables do not need to be conditioned.

Different Ways to Dry Food Defined

In Pennsylvania, we do not have the proper weather and humidity to dry food outside, but there are states like California that are able to use the sun to dry food outside.

Outdoor Drying

Sun Drying can be used to dry high-sugar acidic fruits. A minimum temperature of 85°F with low humidity and a breeze is needed for drying fruit outside. An example of where sun drying is possible is in San Joaquin Valley, California where grapes are dried into raisins. Fruit is placed on racks or screens and placed on blocks to dry.
Solar Drying uses the sun like sun drying but improves upon the process. Solar dryers use a reflective surface like aluminum foil to increase the temperature of the sun by 20 to 30°F. Vents are at each end of the dryer, so air movement is more efficient. Plastic is used to cover the dryer preventing issues if bad weather or water condensation occurs.
Vine drying is used to dry beans outdoors by leaving bean pods on the vine until the beans rattle in the pod. The vine and pod will shrivel when dry.

If fruits and beans are dried outside, they must be treated to kill any insects or their eggs from surviving in beans and fruit.

Treating insects can be done in two different ways (i.e., Freezer Method or Oven Method) to kill any insects or their eggs from surviving in beans and fruit that have been dried outside.
-- Freezer Method – seal dried food in a freezer bag and place the bag in the freezer at 0°F for 48 hours or longer.
-- Oven Method – food is placed on a baking tray and heated in the oven at 160°F for 30 minutes.

Indoor Drying

In Pennsylvania, we must dry food and herbs indoors to be safe. Food can be dried using appliances.

Oven drying can be done if the thermostat of your oven is adjustable to 140°F. Jerky, fruit leather, banana chips, celery, and mushrooms can all be dried using this method. To make sure the oven allows evaporating moisture to escape, the door of the oven must be propped open 2-6 inches and a fan is placed outside the oven door to help air circulation. Caution – do not dry foods using your oven if you have small children in your home.
Room Drying. Some foods can be dried indoors in a well-ventilated area. Bundles of hot peppers and herbs are examples of foods that can be hung indoors or placed on open racks to dry.
Microwave Drying. Parsley, basil, and celery leaves can be dried using a microwave. Follow a microwave instruction manual on drying herbs. Microwave ovens with a wattage rating of 1,000 or higher may heat too fast to use this method. Wash and dry herbs, and arrange them one layer thick between microwave-safe paper towels. The length of time the herbs take to dry will depend on the amount of herbs and the power level of the microwave oven. Microwave for 2-3 minutes per cup. Start with 1 minute, mix after every 30 seconds, and continue to check for dryness. Be careful not to start a fire in the microwave when drying herbs – paper towels can catch fire.
-- Consult Let's Preserve: Drying Herbs for detailed instructions on drying herbs.
Dehydrators are electric appliances that can be used to dry food indoors. Inside a dehydrator, there is a heating element and a fan to dry the food. Fruits, leather, vegetables, and jerky are dried in a dehydrator at 140°F. Herbs can be dried in a dehydrator at 95-125°F. There are two types of dehydrators.
-- Vertical dehydrator has a heating element located at the top or the bottom of the appliance. Air circulates around the unit through the center and around the food. The advantages of a vertical dehydrator are its lower cost and it is usually a compact unit that does not take up much counter space. A disadvantage is if different foods are dried together in a vertical dehydrator flavors can mix – best to dry similar products together. Lastly, the racks may need to be rotated during the drying process to achieve complete drying of an item. Read a unit's manual for instructions to determine if racks need rotating.
-- Horizontal dehydrator has its heating element and fan located on the side or back of the unit. Advantages of a horizontal dehydrator are flavor mixing is reduced, all trays get equal heat and juices do not drip into the heating element. Disadvantages of a horizontal dehydrator can be the cost as some units can be costly and this type of unit takes up more counter space than a vertical dehydrator.