Michigan State University Extension
Preserving Food Safely - 01600525


  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                              

   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

  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.                                       

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

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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