Thursday, November 29, 2007

Pretreating Fruits

Decomposition from enzyme action during storage is less a problem with fruits than it is with vegetables. Fruits have higher levels of sugar and acid, which counteract enzyme action. Although pretreating fruit is not necessary, you can use an ascorbic acid/citric acid dip, a salt solution dip, syrup blanching, a honey dip, or a sulfiting procedure. Certain fruits, such as apricots, pears, peaches, and some varieties of apples, tend to discolor with drying. Pretreating those fruits can decrease browning during processing and storage and lower losses of flavor and of vitamins A and C. If you use a pretreatment method that requires soaking fruits in a water solution, you will need to increase drying time because the fruit will absorb some water. Do not allow foods to soak more than 1 hour.

Ascorbic Acid/Citric Acid Dips. Ascorbic acid/citric acid dips are often used as a pretreatment for fruits. They prevent fruits such as apples, pears, peaches, and apricots from turning brown when cut and exposed to air. An ascorbic acid dip also increases the vitamin C content of the dried fruit. (Ascorbic acid is another name for vitamin C.) Use U.S.P. ascorbic acid or food-grade ascorbic acid, which are seasonally available among canning supplies in supermarkets. Vitamin C tablets can also be used.

To prepare an ascorbic acid solution, combine 1/2 teaspoon of ascorbic acid crystals, or three crushed, 500-milligram tablets of vitamin C, with 1 quart water. Stir until the ascorbic acid dissolves. Place the cut fruit in the ascorbic acid solution. Stir the fruit to ensure even coating. Leave the fruit in the ascorbic acid solution for about 5 minutes. Approximately 1 quart of solution will treat 8 cups of fruit. Pineapple juice or juice from citrus fruits such as oranges, lemons, or rapefruit can also be used as a pretreatment. These juices contain a mixture of citric and ascorbic acids. However, citric acid is a weaker acid than ascorbic acid and is less effective as a pretreatment. You can also use a commercial pretreatment such as the anti-darken-ing powders often sold with food preservation supplies. Follow the label directions.

Salt Solution Dip.

Prepare a solution of 2 to 4 tablespoons of salt per gallon of water. Soak fruit for 2 to 5 minutes, and then drain it well.

Syrup Blanching.

Prepare fruit for drying. Prepare a sugar syrup made with 1 part sugar and 2 parts water. If desired, use less sugar. Bring the syrup solution to a boil. Add the fruit, simmer for 5 minutes, then drain the fruit. Place the fruit on drying trays and dry. This fruit product is like a candied fruit.

Honey Dip.

A honey treatment for fruit can effectively minimize browning and softening in light-colored fruit. Prepare a honey-water dip using 1 part honey to 4 parts water. Dip the fruit in the honey solution immediately after slicing, let it soak for about 5 minutes, and drain well. The dried fruit will have a slight honey taste.


Sulfur dioxide treatments, either sulfiting or sulfuring, are very effective for retarding oxidation and browning in fruit. Fruit flavor and storage life may also improve. Almost all commercially produced light-colored fruits, such as dried apples, pears, and apricots, are treated with sulfur compounds.

However some people have severe allergic responses to sulfur compounds. They should not eat or work with dried fruit pretreated with sulfur or sulfite compounds. Sulfuring, a complicated and potentially dangerous procedure, is no longer recommended. Sulfiting involves preparing a solution of water and a sulfiting agent and then soaking the cut fruit in the solution. In the United States six sulfur compounds (sulfur dioxide, sodium sulfite, sodium bisulfite, potassium bisulfite, sodium metabisulfite, and potassium metabisulfite) have been listed by the U.S. Food and Drug Administration (FDA) as “Generally Recognized as Safe” (GRAS). The most popular sulfiting agents for home drying are sodium bisulfite, sodium sulfite, and sodium metabisulfite. They should be either U.S.P. (food grade) or reagent grade (pure). They are available at most wine-making supply centers and some larger supermarkets.

Amount of sulfur to add per quart of water

Sodium bisulfite 1/2 to 1 teaspoon

Sodium sulfite 1 to 2 teaspoons

Sodium metabisulfite 1 to 3 teaspoons

The sulfiting process has two steps:

1. Prepare the sulfiting solution in a large glass container just before use. Place the cut fruit in the solution. Do not leave the fruit in the sulfiting solution too long or the fruit will be mushy. Use about 10 minutes for sliced fruit and 30 minutes for halved fruit. Do not exceed the recommended quantities of sulfites or soak times.

2. After sulfiting, remove the fruit and drain it well. Some people recommend a quick rinse in cold water before drying. Place sulfited fruit on drying trays and dry. Drying times for sulfited fruits are longer because the fruit absorbs some water during soaking.

Allergic Reactions to Sulfites

Some individuals, particularly those with asthmatic conditions, are highly sensitive to sulfites. During the drying process, most of the sulfites enter the air, leaving only a trace on the fruit. Nevertheless, this trace may cause severe allergic reactions in sensitive individuals. Sensitive individuals should not eat food treated with sulfites or prepare soaking solutions with sulfites. If you use a sulfiting pretreatment when drying foods, be sure to say so on the label.

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