Michigan
State University Extension
Preserving
Food Safely - 01600512
10/13/97
Some fruits, such as peaches, apples, pears and apricots
darken when exposed to air and during freezing. Directions
for such fruits list antidarkening treatment as part of
the freezing preparation. Several types of antidarkening
treatments are used because all fruits are not protected
equally well by all treatments.
Ascorbic acid
For most of the fruits that need antidarkening treatment,
ascorbic acid (vitamin C) may be used. This is very
effective in preserving color and flavor of fruit and adds
nutritive value.
Ascorbic acid is available at drug stores in various
sized containers from 25 to 1,000 grams. (Ascorbic acid may
be obtained also in powdered form.) One teaspoon weighs
about 3 grams; thus there are approximately 8 teaspoons
of ascorbic acid in a 25-gram container. In the recipes,
amounts ascorbic acid are given in teaspoons.
Ascorbic acid tablets can be used but are more expensive
and more difficult to dissolve than the crystalline form.
Also filler in the tablets may make the syrup cloudy. The
amount of ascorbic acid in tablets is usually expressed in
milligrams.
To use, dissolve ascorbic acid in a little cold water. If
using tablets, crush them so they will dissolve more easily.
In syrup pack, add the dissolved ascorbic acid to the
cold syrup shortly before using. Stir it in gently so you
won't stir in air. Solutions of ascorbic acid should be
made up as needed. Keep syrup in refrigerator until used.
In sugar pack, sprinkle the dissolved ascorbic acid over
the fruit just before adding sugar.
In unsweetened pack, sprinkle the dissolved ascorbic acid
over the fruit and mix thoroughly just before packing. If
fruit is packed in water, dissolve ascorbic acid in the
water.
In fruit juices, add ascorbic acid directly to the juice.
Stir only enough to dissolve the ascorbic acid.
In crushed fruits and fruit purees, add dissolved
ascorbic acid to the fruit preparation and mix.
Ascorbic acid mixtures
There are on the market special anti-darkening
preparations--usually made of ascorbic acid mixed with
sugar or with sugar and citric acid. If you use one of
these, follow the manufacturer's directions. In these
mixtures ascorbic acid is usually the important active
ingredient. Because of its dilution with other materials,
ascorbic acid purchased in these forms may be more expensive
than the pure ascorbic acid.
Citric acid, lemon juice
For a few fruits, citric acid or lemon juice (which
contains both citric acid and ascorbic acid) makes a
suitable antidarkening agent. However, neither is as
effective as pure ascorbic acid. Citric acid or lemon juice
in large quantities will mask the natural fruit flavors or
make the fruits too sour.
Citric acid is available at drugstores. When using
citric acid, dissolve it in a little cold water before
adding to the fruit according to directions for that fruit.
Steam
For some fruits, steaming for a few minutes before packing
is enough to control darkening. Steaming works best for
fruits that will be cooked before use.