Enzymes in fruits and vegetables are responsible for color and flavor
changes during ripening. These changes will continue during drying and
storage unless the produce is pretreated to slow down enzyme activity.
Blanching is the recommended pretreatment for vegetables. It helps save
some of the vitamin content, sets color, and hastens drying by relaxing
tissues. Blanching may also prevent undesirable changes in flavor during
storage, and improve reconstitution during cooking.
Steam blanching is preferred because it retains more water-soluble
nutrients than water blanching. Blanching times differ, depending on the
type of vegetable being dried. Overblanching leads to excessive leaching
of vitamins and minerals. Inadequate blanching will not destroy enzymes
that cause vitamin loss during drying and storage.
Many light-colored fruits (especially apples, apricots, peaches,
nectarines, and pears) tend to darken during drying and storage. To
prevent this darkening, the fruit may be pretreated by blanching or by a
suitable dip, but effectiveness of pretreatment methods varies.
Fruit may be dipped in one of the following:
--A solution of table salt
--A solution of ascorbic acid. Commercial antioxidant mixtures
containing ascorbic acid may also be used, but often are
not as effective as pure ascorbic acid.
Fruits may be steam-blanched. However, blanched fruits may turn soft and
become difficult to handle.
Sirup blanching may help retain the color of apples, apricots, figs,
nectarines, peaches, pears and plums. A sweetened candied product will
result.
Fruits with tough skins (grapes, prunes and small dark plums, cherries,
figs, and some berries) may be water-blanched to crack the skins. This
will allow moisture inside to surface more readily during drying.
Before drying pretreated food, remove any excess moisture by placing the
food on paper towels or clean cloths. Drying trays should be loaded with
a thin layer of food as directed. If needed, clean cheesecloth can be
spread on the trays to prevent food pieces from sticking or falling
through.
The amount of food being dried at one time should not exceed that
recommended by instructions.