Transcript NMSU Dehydration

Food preservation: Dehydration
Dehydration
• One of the oldest methods of preserving
food
• Alternative to canning & freezing
• Simple, safe and easy to learn
• Can dry year round
• No refrigeration needed
• Takes little space
How Drying Preserves
• Removes moisture from food so
bacteria, yeasts & molds can’t grow and
spoil food
• Slows down action of enzymes but
doesn’t inactivate them
Temperatures for Drying
• Optimum temperature for drying food is
140°F
• If higher temps are used, food cooks
instead of drying
• Avoid “case hardening” – dried outside
and moisture is trapped inside – mold
results
Helps Drying…
• Low humidity aids drying
• Increasing air current speeds up drying,
removes air around food
Ways To Dry Food
• Foods can be dried in the sun, but often
doesn’t work well in high humidity areas
• Need several days of high temp and low
humidity
• Dry in an oven
• Dry in food dehydrator
Drying Out-Of-Doors
• Sun Drying
– Dry fruits, high sugar & acid make them
safe
– Don’t dry vegetables or jerky/meat
outdoors
– Need hot, dry, breezy days
– Temp of 85ºF. or higher, for several days
with humidity below 60%
– Need to cover, watch materials used and
control for insects and pests
Out-Of-Doors
• Solar Drying
– Need to make a dryer
– Need to stir and turn food several times a day
– Need several days…
• Vine Drying
– Dry beans, lentils and soybeans
– Leave bean pods on vine until beans inside rattle
– If not dried can dry further in oven or dehydrator
Pasteurization
• Freezer Method –
seal food in freezer
plastic bags. Freeze
at 0ºF for at least 48
hours
• Oven Method –
Place food in single
layer on fray or in
shallow pan. Place
in oven preheated to
160ºF for 30
minutes
Drying Foods Indoors
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Food dehydrators
Counter-top
Convection ovens
Conventional ovens
Food Dehydrators
• Small electrical appliance for drying
foods indoors
• Electric element for heat & fat and vents
for air circulation
• Dry foods fast at 140ºF
• Buy at department stores, mail-order,
garden supply, internet
Costs?
Costs vary depending on
features. Some are expandable
& extra trays can be purchased.
Twelve square feet of drying
space dries about a half-bushel
of produce.
Major disadvantage of
dehydrator is limited capacity.
Dehydrator Features
• Double wall
construction of
metal or high grade
plastic, not wood
• Enclosed heating
element
• Counter top design
• Enclosed thermostat
from 85ºF-160ºF
• Fan or blower
• 4-10 open mesh trays,
plastic, sturdy,
washable
• UL seal
• 1 year guarantee
• Convenient service
• Dial for regulating temp
• A timer, auto- shut off
Types of Dehydrators
• Horizontal Air Flow –
Heating element and fan
are located on side
Major advantages –
reduces flavor mixing
so different foods can
be dried at once, all
trays get equal heat,
juices don’t drip into
heating element
• Vertical Air Flow –
Heating element and fan
located at base
Major disadvantage –
if different foods dried,
flavors can mix and
liquids can drip into
heating element
Oven Drying
• Slower than dehydrators, unless you
have a convection oven, which has a
fan
• Take 2 times longer to dry in oven than
dehydrator…oven not as efficient and
uses more energy
Using Your Oven
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Dial needs to go down to 140ºF
Leave oven door propped oven 2-6 inches
Best if you place a fan outside oven door
Oven temp varies…so need accurate oven
thermometer to be sure 140 is achieved
• Trays should clear sides of oven & 3-4”
shorter front to back of oven, 2-3” between
racks in oven
Room Drying
• Herbs, hot peppers, & nuts in shell are
most common air dried foods
• Herbs & peppers – strung on string or
tied in bundles and suspended from
overhead racks in air until dry.
• Can enclose in paper bags, with
openings for air circulation
• Spread nuts in single layer on paper
Drying Fruit
• Preparing the Fruit – wash fruit and core, if
needed
• Fruits can be halved or sliced and some left
whole
• Thin, uniform, peeled slices dry fastest
• Apples can be cored and sliced - wedges,
rings
• Bananas can be sliced
• If fruit dried whole, “check” or crack the skin
to speed drying – cranberries – place in
boiling then cold water to “check”
Pretreating the Fruit
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Sulfuring
Sulfite Dip
Ascorbic Acid
Ascorbic Acid
Mixtures
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Fruit Juice Dip
Honey Dip
Syrup Blanching
Steam Blanching
Drying the Fruit
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Place fruit in single layer
Follow directions given
Follow approximate drying times given
Watch food as it dries much faster at
the end of drying period
Determining Dryness of Fruit
• Most fruit – should have 20% moisture
content when dried
• Cut several cooled pieces in
half…should be no visible moisture and
should not be able to squeeze any
moisture from fruit
• Not be sticky or tacky
• If piece folded in half, shouldn’t stick to
itself
After Drying…
• Cool fruit 30-60 minutes before
packaging…don’t pack too soon or
moisture buildup could occur…don’t
wait too long or could pick up moisture
Conditioning Fruits
• Conditioning equalizes the moisture.
• Pack cooled fruit in plastic or glass jars,
seal and let stand for 7-10 days
• Shake jars daily to separate pieces and
check for moisture condensation
• If condensation, return to dehydrator for
more drying…unless has started to
mold, then dispose of
Drying Vegetables
• Preparing the vegetables
– Wash, trim, peel, according to directions
– Uniform pieces
– Dry as soon as possible after picking
Pretreating Vegetables
• Water blanching –
follow times given,
start counting time
as soon as water
returns to boil. If
takes more than 1
minute to return to
boil, are putting in
too many
vegetables at a time
• Steam blanching –
Vegetables should
be no more than 2
inches deep above
boiling water. Cover
and steam
according to
directions given for
each vegetable
Cooling Vegetables
• Dip briefly in cold water only long
enough to stop cooking
• Cool to they feel only slightly hot to
touch…about 120ºF
• Wipe vegetables and place in
dehydrator
Determining Dryness
• Dry vegetables until brittle or “crisp”
• Some vegetables shatter if hit with
hammer
• 10% moisture
• Don’t need conditioning like fruits, as
lower moisture content
Fruit Leathers
• Fresh Fruit
• Canned or Frozen Fruits
Drying Fruit Leathers
• Pour 1/8-inch thick on drying tray
• Take 6-8 hours to dry in dehydrator, up to 18
in oven
• Dry at 140ºF
• Dry when no indention in center of leather
• When warm, peel from plastic and roll , cool
and rewrap roll in plastic
• Keep up to 1 month at room temp, then may
freeze up to 1 year
Jerky
• Lean meat like beef, pork, venison or
smoked turkey breast
• If wild game is used, treat to kill
Trichinella parasite by freezing a portion
6 inches or less thick at 0ºF at least 30
days…this doesn’t kill bacteria though
Eliminating E. coli O157:H7 Risk
• Heating meat strips • Heating dried jerky
strips in oven after
in marinade before
drying process is
drying – drying times
completed. Heat strips
will be reduced.
10 minutes in oven
Check temp of
preheated to 275ºF.
several strips with
Thicker strips may
metal stem-type
take longer heating,
thermometer to
check temp (160ºF)
determine 160ºF is
with thermometer.
reached.
Storing Jerky
• Properly dried jerky keeps at room temp
for 2 weeks in sealed container.
• For best results, to increase shelf life
and maintain best flavor and quality,
refrigerate or freeze jerky.
Reference
• “So Easy To Preserve”
• Cooperative Extension Service
• The University of Georgia, 4th Edition,
1999.
• Jananne Finck, MS, RD.
Nutrition & Wellness Educator
Springfield Center