Transcript Drying Foods - Food preservation

Drying Foods at Home
National Center for Home Food Preservation
http://nchfp.uga.edu
Disclaimers
• This slide show is a description of principles and considerations in food
dehydration at home.
• It is not intended to be complete directions or instruction for drying specific
foods. It was developed to help educators teach classes in home food
dehydration.
• References to commercials products, services, and information is made with
the understanding that no discrimination is intended and no endorsement by
the University of Georgia, U.S. Department of Agriculture and supporting
organizations is implied. This information is provided for the educational
information and convenience of the reader.
A long, long time ago, in a far
away place…
• One of the oldest methods of preserving food
• Evidence of Middle Eastern and oriental cultures
drying foods in 12,000 B.C.
• Sun and wind- natural dryers
• Fire creates heat to dry in still houses
• Electricity
• Cylindrical commercial dehydrator design
patented in 1980
Why dry?
•
•
•
•
•
Simple
Minimal equipment, supplies, and ingredients
Reduces size and weight of food
Long shelf life
Requires little space
Why not dry?
• Time- 1 (parsley) to 48 (peaches) continuous
hours in dehydrator…2 to 6 days under the sun
• Attention – watch, stir, turn, test for dryness
• Preparation is same as for canning or freezing
• Not suitable for all foods
How does drying preserve?
• Microorganisms (yeast, mold, bacteria) need
water to grow, so removing moisture prevents
spoilage from microorganisms.
– Concerns with jerky and foodborne illness
• Enzyme action is slowed (though not stopped),
which means that color, texture, and quality do
not degrade as rapidly once food is dried.
Choosing a method of drying
• You must be able to control:
– Air circulation
– Moving air encourages evaporation by maintaining low humidity
– Temperature
– 140°F ideal for most foods
– Too slow (low temp., poor air circ.)=microorganisms could grow
– Too fast (high temp., rapid air circ.)=cooked food or “case hardening”
 “Case hardening” is when the outside dries but moisture is trapped
inside, resulting in mold.
Methods
Outside:
Sun
Solar
Vine
Inside:
Room
Oven
Dehydrator
Sun drying
• For: foods high in sugar and acid (fruits) and very few vegetables (whole
peppers, beans, peas)
• Weather:
• Hot- 85°F or higher
• Dry- less than 60% humidity
• Breezy
• Work:
•
•
•
•
Build racks or screens
Turn 2-3 times per day and cover or bring in at night
Cover with cheesecloth and control for insects and pests
Pasteurization
• +/- : low cost, high yield/ takes several days
Solar drying
• For: foods high in sugar and acid (fruits) and a few vegetables (whole
peppers, beans, peas)
• Weather:
– Similar to sun drying, except that temp.
increases by 20°F-30°F and air flow increases
• Work:
– Make the dryer (aluminum foil/glass, plastic sheet)
– Turn food 2-3 times a day
– Pasteurization
• +/- : low cost /lower yield than sun drying, takes several days
Vine drying
• For: beans (navy, kidney, butter, great northern), lentils, and soybeans
• Weather:
• Same as sun drying
• Work:
• Minimal- leave bean pods on vine until they rattle
• Pasteurization
• +/- : low cost/takes several days, may need additional drying method
Pasteurization
• Required for all methods of drying outdoors
• Done after drying to kill insects and their eggs
1. Freezer method:
2. Oven method:
Seal food in freezer
bags/containers and
place in freezer set at 0°F
or below for at least 48
hours.
Place food in a single
layer on a tray or pan and
put into an oven preheated
to 160°F for 30 minutes.
Room drying
• For: herbs, nuts, chili peppers, and partially dried fruits
• Space/equipment:
• Sunny room- 80°F and low humidity
• Fan for air movement
• Trays, string, or paper bags
• Work:
• String herbs or peppers in bundles and suspend in air
• Spread nuts in single layer on paper, tray, or in paper bag
• +/- : low cost/takes several days
Oven drying
• For: Most foods
• Equipment:
• Oven which registers 140°F- 150°F
• Fan for air movement
• Cookie sheets and liners or cooking spray
• Work:
•
•
•
•
Set oven racks 2 to 3 inches apart
Place foods in single layer on cookie sheets
Keep oven door open 2 to 6 inches and place fan nearby
Rotate foods occasionally and watch for scorching
• +/- : relatively low cost/high energy use, ties up oven
Dehydrator drying
• For: most foods, except milk products and eggs
• Equipment:
• Dehydrator with trays
• Electrical supply
• Work:
• Buy dehydrator
• Occasional turning and testing for dryness
• +/- : high quality, sanitary, fast/high cost, limited capacity
Dehydratorsfeatures to look for ?
•
•
•
•
•
•
•
•
•
Double wall
Metal or high grade plastic (not wood)
Enclosed heating element
Counter-top design
Enclosed thermostat
Dial to regulate temperature
Auto shut-off timer
Fan or blower
Plastic, sturdy, washable mesh trays
Look for:
• UL seal
• At least 1 year guarantee
• Convenient service
Dehydrator designwhat’s the difference?
Horizontal air flow- heat & fan on side
 Reduces flavor mixing
 Equal heat dispersal
 No dripping onto heating element
 Limit on height of food pieces
Vertical air flow- heat & fan in base/lid
 Flavors might mix
 Uneven heat dispersal unless trays
rotated
 Liquids might drip onto heating
element; choose fan in lid
Andress, E.L. and Harrison. J.A. (2011). So Easy to Preserve, 5th ed. Cooperative
Extension, University of Georgia. p. 322.
Don’t try to dry like this…
• Heat vent drying
• Microwave drying, except herbs
– And only if your oven manufacturer allows it.
What food products
can you dry ?
•
•
•
•
•
•
Fruits
Vegetables
Leathers
Jerkies
Herbs
Nuts and seeds
Fruits – Preparation
•
•
•
•
•
Wash
Core if needed
Uniform pieces- whole, halved, or sliced
Peeled and thinly sliced dries fastest
“Check” whole fruits with thick skins (ex: cranberries)
• Place in boiling water until skin cracks, then quickly place
into cold water to prevent cooking.
Fruits – Pretreatment
To prevent immediate and long-term darkening
•
•
•
•
•
•
•
•
Sulfuring
Sulfite dip
Ascorbic acid
Ascorbic acid mixtures
Fruit juice dip
Honey dip
Syrup blanching
Steam blanching
Longest lasting: Sulfur
1. Sulfuring
 Outdoors only
 Adverse reactions possible
2. Sulfite dip
 Adverse reactions possible
 For one quart of water use:



¾ to 1½ tsp. sodium bisulfite
1½ to 3 tsp. sodium sulfite
1 to 2 Tbsp. sodium meta-bisulfite
 Soak slices 5 minutes, halves 15 minutes
 Rinse
Least concern: Ascorbic acid
3. Ascorbic acid
 For 2 cups water, add 1 tsp.
 Soak 3 to 5 minutes, drain.
4. Ascorbic acid mixtures
 For 1 quart water, add 1to 1½ tsp.
 Soak 3-5 minutes, drain.
Flavor (and calories) added: Dips
5. Fruit juice dip
 Choose juice high in vitamin
C (orange, lemon, pineapple,
grape, or cranberry)
 Soak 3 to 5 minutes, drain
6. Honey dip
 To 1½ cups boiling water,
add and mix ½ cups sugar
 Cool, then add ½ cups
honey.
 Soak 3 to 5 minutes, drain.
Sweet and simple: Blanching
7. Syrup blanching
 Boil 2 cups water, 1 cup sugar,
and 1 cup light corn syrup
 Add 1 pound fruit
 Simmer 10 minutes
 Remove form heat and let
stand 30 minutes
 Rinse lightly and drain
8. Steam blanching
 Boil water, lower fruit according to blanching times
Fruits – Drying
• Single layer
• Follow directions and drying times
provided
• Watch food carefully at the
end…dries much faster!
• Dry until doesn’t stick or have any
visible moisture- Tests: fold in half,
squeeze
• No more than 20% of original
moisture should remain for
storage.
Fruits – Conditioning
• Cool 30 to 60 minutes
– Packaging too soon = too much moisture
could be retained
– Too late = moisture could be picked-up
• Condition to equalize:
– Seal in container for 7 to10 days, shaking
occasionally
– If you see condensation, dry some more
• Store in dry, moisture-proof containers
Vegetables –Preparation
• Select freshly picked,
high quality veggies
• Wash
• Trim and peel as needed
• Make pieces uniform
Vegetables – Pretreating
To inactivate enzymes
Water blanching
Steam blanching
• Fill large pot 2/3 with water
• Bring to boil, then submerge veggies
in a basket or colander
• Start timer (refer to blanching time
table) when water returns to a boil
• If it takes more than one minute to
come to a boil, then there are too
many veggies…reduce amount next
time
• Dip veggies in cold water quickly–
until just slightly hot – to stop
cooking
• Pat veggies dry and place in on tray
• Add water to large pot, only so full
that the steamer basket will not
touch the water
• Bring to boil, then place veggies in
the basket
• Cover with lid and steam according
to time given in directions
• Dip veggies in cold water quickly –
until just slightly hot – to stop
cooking
• Pat veggies dry and place in on tray
Vegetables –Drying
• Dry until brittle or crisp
– Some vegetables shatter if hit with a hammer!
• Store in airtight containers with no more than
10% of original moisture
• Lower moisture content results in no need for
conditioning
Leathers…fruits AND veggies
• Fun way to mix flavors (ex: banana blueberry)
• Can use fresh, canned or frozen fruits
• Can also use tomatoes, pumpkin puree, or
mixed vegetables (tomato, onion, celery)
Leathers – Preparation
• Wash fruit
• Peel if needed, and cut into small pieces
• Add lemon juice or ascorbic acid to prevent
browning of light colored fruit
– 2 tsp. lemon juice or 1/8 tsp. ascorbic acid per 2 cups fruit
• Purée until smooth
• Add sugar, honey, or corn syrup if desired
Leathers – Drying
• Line cookie sheet with plastic wrap or use dehydrator tray insert
• Pour 1/8 inch thick, individual or large
• Dry at 140°F for 4 to 6 hours (individual) or 6 to 8 hours (large),
or up to 18 hours in an oven, or 1 to 2 days in the sun
• Dry until no indentation from touch in center
• Roll in plastic wrap and store in moisture-proof container for up
to one month at room temp.
Jerky – Preparation
•
•
•
•
Use only lean meat (beef, pork, venison, smoked turkey breast)
Slice meat to ¼ inch thick
Place in pan with marinade and let sit 1 to 2 hours or overnight
For wild game:
– Treat to kill Trichinella parasite by freezing piece no more than 6 inches
thick at 0°F for at least 30 days
• Treat pork by freezing piece no more than 6 inches thick at 5°F
for 20 days
• Heating is necessary to eliminate E. coli O157:H7 risk
– Heat jerky to 160°F using prescribed methods for pre- or post-drying
– Eating jerky dried at 140°F (or below) may pose bacterial risk
Jerky – Heating
1. Heat prior to drying
• Refrigerate strips in marinade
• Boil strips in marinade for
5 minutes
• If possible, check temp. of
thickest strips with metal
stem-type thermometer to
make sure they are 160°F
• Drain
• Place in dehydrator
preheated to 140°F
2. Heat after drying
• Preheat oven to 275°F
• Place dried strips on cookie
sheet, not overlapping
• Heat 10 minutes (at least)
• Check temp. (160°F) of
thickest strips with metal
stem-type thermometer
Jerky – Drying
•
•
•
•
•
•
Do not dry outside
Marinate
Dry at 140°F
Begin checking for dryness after 3 hours
Dry when cracks, but does not break when cool
Store jerky in sealed container at room temp. for
2 weeks, or refrigerate/freeze for longer shelf life
Herbs – Preparation
•
•
•
•
Harvest herbs before flowers open
Rinse in cool water and shake off excess water
For room drying – bundle and tie
For oven drying – separate leaves from stems and lay
on paper towel, up to five layers on top of each other
• For dehydrator and microwave drying, place herbs in
single layer on tray
Herbs – Drying (in Room)
•
•
•
•
Simply expose to warm, dry, well-ventilated air
Sun drying is not recommended
Done when leaves crumble and stems break
Sturdy herbs like rosemary, sage, thyme, and parsley are
easy to tie in small bundles and hang
• Tender herbs like basil, oregano, tarragon, and mint can
also be hung in small bunches
– Hang inside paper bags with holes in the sides
– Close top with a rubber band
Herbs – Drying
in Electrical Appliances
• Use a cool oven with only the oven light or pilot light
on
– Will dry overnight
• Set dehydrator to only 95°F to115°F
– Drying times vary from one to four hours
• Check periodically – done when herbs crumble and
stems break when bent
• Microwaves can be used to dry small quantities
– Only IF your oven manufacturer allows it.
Nuts and Seeds – Preparation
• Not the same as roasting
• Can dry some seeds (like sunflowers) on plant
• Wash seeds and place in single layer; peanuts can be
shelled or unshelled
• Option 1: Dry outside in sun
• Option 2: Dry in dehydrator at 100°F to 130°F
(depending on which seed or nut) for 1 to 2 hours
• Option 3: Dry in warm oven for 3 to 4 hours
• Stir frequently
Helpful hints
• Don’t mix foods with strong smells or drying times.
• Use vegetable oil, vegetable spray, or cheesecloth to
prevent sticking to trays.
• Don’t overlap pieces of food on drying trays.
• Remember, the larger the load, the longer the drying time,
the more nutrients lost.
• Rotate racks and turn foods periodically.
What to do with dried foods?
• Eat and enjoy as is!
• Fruits:
– Plump or soften:
• Cover with liquid for 5 to 10 minutes
• Steam 3 to 5 minutes
• Soak, then simmer
• Vegetables:
– Soak 1 to 2 hours in 1 to 2 cups liquid per 1 cup veggies
– Add straight to soup, without soaking
Control points
•
•
•
•
•
•
•
Cleanliness is key.
Follow 2 hour rule with perishables.
Marinate meat in refrigerator.
Preheat dehydrator to 140°F (or required temp).
Avoid case hardening.
Cool to room temperature before packaging.
Store in cool, dark, dry conditions.
Credits
• This material is based upon work supported by the Cooperative State
Research, Education, and Extension Service, U.S. Department of Agriculture,
under Agreement No. 00-51110-9762.
• Photography and illustration credits:
– Elizabeth L. Andress, Elaine D’Sa, and Kasey Christian. National Center
for Home Food Preservation, University of Georgia.
– Andress, E.L. and Harrison, J.A. Preserving Food: Drying Fruits and
Vegetables. Athens, GA: University of Georgia Cooperative Extension.
Specific credits can be provided for re-use of any individual photo taken by the University of Georgia.
Reference materials
• Andress, E.L., Harrison, J.A. (2011). So Easy to Preserve,5th ed. Athens, GA:
University of Georgia Cooperative Extension.
•
Nummer, B.A. (2002). Historical Origins of Food Preservation. Athens, GA: The University
of Georgia, National Center for Home Food Processing and Preservation.
http://nchfp.uga.edu/publications/nchfp/factsheets/food_pres_hist.html.
•
Erickson, C.S.( 1980). United States Patent 4190965.
http://www.google.com/patents?id=h9gtAAAAEBAJ&zoom=4&dq=history%20of%20de
hydrators&pg=PA1#v=onepage&q=history%20of%20dehydrators&f=false.
•
National Academy of Engineering. (2013). Greatest Engineering Achievements of the 20th
Century. http://www.greatachievements.org/?id=2990.
Document Use
– Permission is granted to reproduce these materials in whole or in part for
educational purposes only (not for profit beyond the cost of reproduction)
provided the authors and the University of Georgia receive acknowledgment and
this notice is included:
Reprinted with permission of the University of Georgia. Andress, E.L. and Christian, K.A.
(2013). Drying Foods at Home. Athens, GA: The University of Georgia, Cooperative
Extension.
– Permission to post on other websites must be requested.
– © University of Georgia