Michigan State University Extension
Preserving Food Safely - 01600525
10/13/97

### PRE-DRYING FRUIT TREATMENT

     Sort  and discard defective fruits.  Wash, pit  and  halve

    when
     necessary (as with stone fruits).  Most fruit must  be

    pretreated
     immediately   before  drying  to   maintain   an

    appetizing
     appearance--and  to prevent darkening,  loss  of

    flavor
    and vitamin C.

     Pretreat  fruit by dipping it in a sulfite,  ascorbic acid

    or
     salt water solution,  by syrup blanching or by  exposing

    the
     fruit  to  sulfur   fumes.   The  sulfur  treatment  is

    preferred
     as  a  pre-drying  treatment.   Sulfuring   fruit

    (exposing
     it to sulfur fumes) effectively  preserves  color

    maintains
    the quality and decreases loss of vitamins A and C

    in
    the fruit during  drying  and  storage.

    PRE-TREATING
    FRUIT WITH SULFUR

    Materials:

      Slatted, wooden trays.  DO NOT USE ALUMINUM OR GALVANIZED

    SCREENING
    MATERIAL, as sulfur fumes corrode most metals.  If

    wooden,
     slatted trays are not available, wooden  lids  from

    lug
    boxes may be used.

     Thread  spools, wooden or plastic (but not  styrofoam)  or

    small,
     wooden blocks.  Place at corners of trays  to  stack

    them
    1 1/2 inches apart.

     A heavy cardboard or wooden (no cracks  or openings)  box.

    Must
    be large enough to place over stacked trays with 1 to 1

    1/2
    inches to spare between the trays and the inside of  the

    box.
      Box  should also be large enough to  accommodate  the

    container
    of burning sulfur under the stacked trays.

     Fire  bricks to raise the stack of trays high  enough  off

    the
    ground to accommodate the container of burning sulfur.

     Sulfur.  Use elemental sulfur also called  Sulfur  Flowers

    (U.S.P.
     standard)  or  flowers of sulfur.  It  is  free  of

    impurities,
     burns  readily  and may be  purchased  at  most

    pharmacies.

     Clean,  metal  container to hold the  sulfur.   For  small

    amounts
     of fruit,  a flat tuna can or an  aluminum  pie tin

    will
    be large enough.

    Procedure

     ALWAYS  USE SULFUR OUTDOORS AWAY FROM CLOSE  CONTACT  WITH

    PLANTS,
    SHRUBS, AND TREES.

     1. Spread fruits in a single layer, pit cavity side or cut

    surfaces
    up, on trays.  Pieces should not touch each other.

     2.  Stack  trays 1 1/2 inches apart, separated  by  spools

    placed
    at the corners.

     3. Cover the stacked trays with the box.  Make a slash  at

    the
    bottom of the box and another slash at the upper edge of

    the
     opposite side.  Open slashes when necessary  to  permit

    circulation
    of sulfur fumes.

     4. Measure the sulfur and place it in the container.   The

    amount
     used varies with the length of time the fruit is  to

    be
    sulfured, weight of the fruit, and the dimensions of  the

    box.
      Generally, if you are using a cardboard box to  cover

    the
      trays,  you will need to use 1 to 2 teaspoon of sulfur

    per
     pound  of  fruit  (weight  before  drying).    If   you

    have
    constructed  a more air-tight sulfuring box from  wood,

    you
    only  need  to use 1 teaspoon of sulfur  per  pound   of

    fruit.
       Sulfur  fumes  do  the  work,   not  the   burning

    so
     it is important that the box be tight.   Sulfuring    is

    complete
      when   fruit  appears  bright    and  glistening,

    and
    a small amount of juice appears in the pit cavity.

     The burning time of sulfur will vary with the ventilation,

    shape
    of container, and weather conditions.

     5.  Place the can of sulfur under the box near  the  lower

    opening
     and light the sulfur.   It melts before it  ignites

    but
     soon  burns with a clear blue flame that  produces  the

    acrid
     sulfur dioxide fumes.   Because of the heat resulting

    from
     the  burning sulfur, space is  necessary  between  the

    sulfur
    and the sides of the box, and between the sulfur  and

    the
     first  tray.   Do  not  leave  burned  matches  in  the

    container
    since they will impede the burning of the sulfur.

     6. Immediately lower the box over the stack, and seal  the

    bottom
    edges with dirt leaving the flap open.

     7.  When sulfur is burning well, close openings in box and

    start
    timing.

    SULFITING
    FRUIT BEFORE DRYING

     Soaking  fruits in a solution of sodium bisulfite  has  an

    effect
     similar to sulfuring.   Mixing sodium bisulfite with

    water
     releases sulfur dioxide which penetrates the  surface

    of
     the fruit,  retarding oxidation and enzymatic  browning.

    Sodium
     bisulfite looks similar to table salt.   Food  grade

    (U.S.P.)
     sodium bisulfite can be purchased  at  wine-making

    supply
     stores or pharmacies.   DO NOT use sodium bisulfate.

    While
     the  two  products  may  seem  similar  in  name  and

    appearance,
    their chemical properties are not the same.  Due

    to
     its chemical structure,  bisulfate is unable to  inhibit

    the
    oxidation and enzymatic browning reactions that cause  a

    fruit
    to ripen.

     Sodium bisulfite is preferred for sulfiting because of its

    strength,
     but  sodium  sulfite or sodium metabisulfite  may

    also
     be  used.    The  strength  ratio  is:   1  tablespoon

    bisulfite=2
      tablespoons   sodium   sulfite=4   tablespoons

    metabisulfite.
      You will need to use 2 times as much sodium

    sulfite
    or 4 times as much metabisulfite to achieve the same

    results
      as  one  part  bisulfite.    Sodium  sulfite   and

    metabisulfite
    can be purchased at wine-making supply  stores

    or
    pharmacies.

     Prepare  a  solution of 1 to 2 tablespoons  bisulfite  per

    gallon
    of water.  Soak fruit slices for 5 minutes and halved

    fruit
    for 15 minutes.  When soaking is completed, remove the

    fruit
     and rinse it lightly under cold tap water.   Pat  dry

    with
    paper towels and proceed with drying.

    NOTE:
    Sodium bisulfite is an antidarkening agent that may be

    used
     to pretreat fruits before drying.   While use of  this

    preparation
     presents  no problem  to  most  people,  recent

    evidence
     suggests that sulfites may cause adverse reactions

    in
    some asthmatic individuals.   Thus, these individuals may

    choose
    to use another type of pretreatment.

    ASCORBIC
    ACID DRYING PRETREATMENT

     Pure  ascorbic  acid (vitamin C) is  an  antioxidant  that

    helps
     to keep fruit from darkening as it is being  prepared

    for
     drying.    Dissolve  2  tablespoons  of  ascorbic  acid

    crystals,
     2  tablespoons  of  ascorbic acid  powder,  or  5

    crushed
    one-gram vitamin C tablets in one quart of  lukewarm

    water.
      Slice  or  chop fruits directly into the  solution.

    Drain
    fruit well before loading onto drying trays.  Ascorbic

    acid
    preparations can be purchased at pharmacies or wherever

    vitamin
     supplements  are sold.      Commercial  antioxidant

    mixtures
    containing ascorbic  acid and  citric  acid are not

    as
    effective as  pure  vitamin  C,  although  they are often

    easier
     to  come  by.   Follow  package  directions  for cut

    fruits
    when using these mixtures.

    SYRUP
    BLANCHING PRETREATMENT

     Syrup blanching will hold natural fruit color fairly  well

    during
     drying  and  storage,  but it  will  produce  softer

    textured
    and sweeter flavored fruit than other methods.

     Prepare  a sugar syrup by mixing 1 cup sugar,  1 cup light

    corn
    syrup and 2 cups water.   Bring the mixture to a  boil.

    Add
     the prepared fruit and simmer for 10  minutes.   Remove

    fruit
     from  heat  and  let stand in the hot  syrup  for  an

    additional
     15 minutes.   Drain fruit well and proceed  with

    drying.

    SALT
    WATER DIP PRETREATMENT

     Dissolve  4 tablespoons of table salt in 1 gallon of  luke

    warm
     water.   Slice  or chop the fruit  directly  into  the

    water.
      Allow  it to soak no more than 10 minutes or  fruit

    will
    absorb too much water and acquire a salty taste.

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