Determining Dryness

A major problem in drying foods at home is determining if and when the food item is dry. Judging when food is dry requires experience, but keep in mind that it is better to overdry than to underdry.

Don't be surprised to find a variety of suggestions for drying methods, temperatures, and lengths of time. When in doubt, continue drying for an additional 15 to 30 minutes, than check for doneness. Allow the product to cool before testing.

The length of time needed for drying will depend on the size and number of pieces dried at one time. Drying fruit can take anywhere from 6 hours for very thin or small pieces such as apple slices or grapes to 10 hours for larger juicy fruits such as peach or apricot halves. Temperature and humidity will also affect the drying time.

The drying process is simply not as precise as canning and freezing because it involves so many different factors. Vegetables must be dried to about 5 percent water content and fruits to 15 to 20 percent water content. Dried fruits are stable at a higher moisture content than dried vegetables because the concentrated natural sugars and acids in the dried fruit function as preservatives.

After foods are dried, allow 30 minutes to one hour cooling time. In general vegetables are dry when they are brittle, fruits when they feel like leather. Too long a cooling period allows moisture from the air to re-enter the food.


VEGETABLES

To determine if vegetables are dry, remove some pieces near the end of the drying process. This time will usually be after a minimum of 6 to 8 hours. Cool the pieces to room temperature. Vegetables are sufficiently dried when they are hard and brittle or tough and leathery, depending on the vegetable. Edges will be sharp. Beans, corn and peas are hard and will shatter when hit with a hammer. Leafy thin vegetables should be brittle. Larger chunks or slices of vegetables should be leather.


FRUITS
 
To determine if fruits are dry, remove a piece of fruit during the end of the drying period. Cool to room temperature. Fruits are adequately dried when moisture cannot be squeezed from them. Most fruits will feel leathery and pliable when properly dried. It should have no pockets of moisture.


FRUIT LEATHERS

Fruit leathers may be slightly sticky to the touch but separate easily from the plastic wrap. For long term storage, dry leathers until they are no longer sticky.


HERBS

Herbs are dried when brittle. Leaves shatter when rubbed together.


MEATS

Meats should be extremely dry unless they are to be refrigerated or frozen for long-term storage. Meat is sufficiently dried when it is dark in color, fibrous, and forms sharp points when broken.

Real Cooking
Did You Know?
Freeze-drying (lyophilization or cryodesiccation) is a special dehydration process typically used to preserve a perishable material or make the material more convenient for transport. Freeze-drying works by freezing the material and then reducing the surrounding pressure and adding enough heat to allow the frozen water in the material to sublime directly from the solid phase to gas.

There are three stages in the complete freeze-drying process: freezing, primary drying, and secondary drying.

If a freeze-dried substance is sealed to prevent the reabsorption of moisture, the substance may be stored at room temperature without refrigeration, and be protected against spoilage for many years. Preservation is possible because the greatly reduced water content inhibits the action of microorganisms and enzymes that would normally spoil or degrade the substance.

Freeze-drying also causes less damage to the substance than other dehydration methods using higher temperatures. Freeze-drying does not usually cause shrinkage or toughening of the material being dried. In addition, flavours, smells and nutritional content generally remain unchanged, making the process popular for preserving food[1]. However, water is not the only chemical capable of sublimation, and the loss of other volatile compounds such as acetic acid (vinegar) and alcohols can yield undesirable results.

Freeze-dried products can be rehydrated (reconstituted) much more quickly and easily because the process leaves microscopic pores. The pores are created by the ice crystals that sublimate, leaving gaps or pores in their place. This is especially important when it comes to pharmaceutical uses. Lyophilization can also be used to increase the shelf life of some pharmaceuticals for many years.