Most vegetables and some fruits (Tables 2 and 3) should undergo a pretreatment, such as blanching or dipping.

Blanching is briefly precooking food in boiling water or steam, and it is used to stop enzymatic reactions within the foods. Blanching also shortens drying time and kills many spoilage organisms.

Steps for steam blanching (fruit and vegetables):

• Use a steamer or a deep pot with a tight-fitting lid that contains a wire basket or could fit a colander or sieve so steam can circulate around the vegetables.
• Add several inches of water to the steamer or pot and bring to a rolling boil.
• Loosely place fruits/vegetables into the basket, no more than 2 inches deep.
• Place basket into pot (fruits/vegetables should not make contact with water).
• Cover and steam until fruits/vegetables are heated for the recommended time (Table 2 and 3).
• Remove basket or colander and place in cold water to stop cooking.
• Drain and place fruits/vegetables on drying tray.

Steps for water blanching (vegetables only):

• Use a blancher or a deep pot with a tight-fitting lid.
• Fill the pot two-thirds full with water, cover, and bring to a rolling boil.
• Place vegetables into a wire basket and submerge them into the boiling water for the recommended time (Table 2).
• Remove vegetables and place in cold water to stop cooking.
• Drain and place vegetables on drying tray.

Steps for syrup blanching (fruits only):

• Combine 1 cup sugar, 1 cup light corn syrup, and 2 cups water in a pot.
• Add 1 pound of fruit.
• Simmer 10 minutes (Table 3).
• Remove from heat and keep fruit in syrup for 30 minutes.
• Remove fruit from syrup, rinse, drain, and continue with dehydration step.

Dipping is a pretreatment used to prevent fruits such as apples, bananas, peaches, and pears from turning brown. Ascorbic acid, fruit juices high in vitamin C (lemon, orange, pineapple, grape, etc.), or commercial products containing ascorbic or citric acid may be used for dipping. For example, dipping sliced fruit pieces in a mixture of ascorbic acid crystals and water (1 teaspoon ascorbic acid crystals per 1 cup of water), or dipping directly in fruit juice for 3 to 5 minutes will prevent browning. Fruits may also be blanched as a means of treatment.