Canning At Home
Rick Sloan
FCS Agent
What will we learn?
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Principles of Canning
Two Methods of Canning
Packing Methods
Canning Equipment
Processing Time
Boiling Water Processing
Pressure Canning Processing
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Principles of Canning
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Canning Basics
 Food is placed in a canning jar and heated to a
temperature that destroys targeted
microorganisms.
 Heat also inactivates enzymes that cause
spoilage.
 Air is driven from the jar during heating. As
the jar cools a vacuum seal is formed.
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Commercial Sterility
 All pathogens, spoilage bacteria, molds, and
yeast are “killed.”
 Those that survive are thermophilic bacteria
that cause spoilage but not illness.
 Some produce gases.
 Some produce bad odors.
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Vacuum Seal
 Holds the lid on the jar.
 Prevents recontamination of the food.
 Prevents air from drying out the food.
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Two Methods of Canning
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Two Methods of Canning
Boiling Water Canning
 Used for high-acid foods
Pressure Canning
 Used for low-acid foods.
 Can also be used for high-acid foods but might
result in a soft texture.
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High-Acid Foods (pH < 4.6)
 All fruits, except for:
 figs
 tomatoes, and
 melons
 Rhubarb
 Fermented pickles, such as sauerkraut
 Acidified foods, such as pickles and tomatoes
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Low-acid Foods (pH > 4.6)
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All vegetables, except for rhubarb
Meats
Poultry
Seafood
Soups
Mixed canned foods (low-acid + high-acid)
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Why Two Methods of Canning?
 Yeast, molds, and most bacteria are killed at boiling
temperatures -- 212ºF at sea level.
 C. botulinum forms spores that require higher
temperatures for destruction in a reasonable period
of time -- usually 240ºF or above at sea level.
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Clostridium botulinum
 Clostridium botulinum bacteria are found naturally in
soil and water.
 Seven known types, but only A, B, E and F cause
illness in humans.
 This bacterium can produce heat-resistant spores.
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C. botulinum -- Growth
To germinate, the spores need the following
conditions:
 anaerobic environment (No Oxygen)
 low-acid food
 temperature between 40ºF and120ºF
 relatively high moisture
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C. botulinum -- Growth
Optimal conditions might be found in:
 Home canned foods
 Smoked fish and sausage
 Foil-wrapped baked potatoes sitting at room
temperature
 Packaged mushrooms
 Pot pies and other foods in gravy
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Botulinum Toxin
 The botulinum toxin, one of the deadliest known,
causes botulism.
 1 mg can kill 655 tons of mice.
 Food can contain toxin without showing any signs.
 Antitoxin available, but slow recovery. Permanent
nerve damage possible.
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Botulism -- Symptoms
Symptoms usually appear within 12 to 72 h after
eating contaminated food:
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Digestive upset (in some cases)
Blurred, double vision
Difficulty swallowing, speaking, and breathing
Possible death from suffocation
10-35% mortality rate
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Preventing Botulism
 Spores do not grow in high-acid foods.
 Spores killed when low-acid foods heated long
enough at a specific temperature.
 Process low-acid foods in a pressure canner,
which can reach a temperature of 240ºF.
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Preventing Botulism
 Prepare and process food according to
instructions in a tested recipe.
 Canner gauge must be accurate and properly
used.
 Use only high quality raw ingredients.
 If toxin is suspected, detoxify food before
discarding. The toxin is destroyed by boiling
even though the spores are not.
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Improperly Canned Foods
 Never consume improperly canned foods.
 Throw out – do not feed to animals.
 Boiling will not always adequately destroy
toxin.
 When cleaning up surfaces contaminated by
unsafe canned foods, prepare a 1:5 bleach to
water solution.
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Packing Methods
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Raw Pack
 For foods that lose shape when cooked.
 Place raw food directly in jars. Pour boiling hot liquid
over the food.
 Pack firmly, do not crush.
 Add jars carefully to warm canner to prevent jar
breakage from heat shock.
 Preheat water to 140oF before putting raw-packed
foods into boiling water bath.
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Hot Pack
 Preferred method for most foods.
 Food is cooked in liquid before packing. Cooking liquid
is then poured over food in jar.
 Less floating of food pieces in the jar.
 Better food color and flavor.
 Easier to pack, foods more pliable
 Heat in preparing kills some microorganisms.
 Preheat water to 180oF before putting into boiling water
bath.
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Canning Equipment
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Pressure Canners
 Flat rack in bottom
 Pressure regulator or indicator:
 Dial or weighted gauge
 Older models have petcocks
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Vent pipe for pressurizing
Safety valves or overpressure plugs
Safety locks when pressurized
Rubber gaskets in lid (metal to metal seal)
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Replacement Parts
 Dial gauges, when inaccurate
 Gaskets (sealing rings)
 Every 2 years usually
 Rubber overpressure plugs
 Every 2 years
 Vent pipes if clogged
 Air vent/cover lock from lid
 Weighted gauges or dead weight if lost
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Processing Time
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Processing Schedules
Definition:
Length of time at a specific temperature that a food
must be processed.
Affected by:
pH value of the food
Composition of the food
- Viscosity
- Tightness of pack
- Convection vs. conduction transfer of heat
- Starches, fats, bones
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Processing Schedules
Affected by:
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Preparation style of food
Initial temperature of food as it is filled into jar
Temperature of processing
Size of jar
Shape of jar
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Significance of Heat Penetration
 Processing time is affected by whether food heats
by convection, conduction, or a combination of
both.
 Heat penetration studies used to scientifically
determine safe processing times.
 The “cold spot” in the food must reach the correct
temperature for the correct length of time to
destroy target pathogens.
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Heat Penetration
Follow recipe exactly.
 The following slows heat penetration:
 Extra sugar or fat
 Oversized food pieces
 Added thickeners
Use recommended canners.
 Heat-up and cool-down times in pressure canners
are counted toward sterilizing value of the
process. Do not rush them.
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Processing Time
 Each food and preparation style has its own
processing time so always use a tested recipe.
 Time differs with size of jar.
 Too little = under processing  spoiled or
unsafe food
 Too much = over processing  overcooked
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Pressure Increases Temperature
 Heat food to 240oF to destroy botulinum
spores. Cannot achieve this in boiling water.
 The only safe way to can low-acid foods is
with pressure.
 Temperature of 240ºF or above needed for
reasonable processing times
 10 psig = 240ºF at sea level
 15 psig = 250ºF at sea level
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Boiling Water
Processing
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Boiling Water Bath
 Have water simmering (180oF) in canner,
high enough to cover jars when filled (about
six inches for most loads).
 Hot packed jars = simmering water
 Raw packed jars = warm to hot water
 Place jars on rack in canner.
 Add more hot water if necessary, once jars
are in canner. (Never pour hot water directly onto
raw-packed jars).
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Boiling Water Bath
 Start counting processing time after water
returns to a full boil.
 Adjust processing time for altitudes over 1,000
feet.
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Boiling Water Bath
 If processing foods for more than 30 minutes,
water should be two inches over jars when
process begins.
 If water stops boiling at any time during
process, bring the water to a boil and begin the
process over.
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Pressure Canning
Processing
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Pressure Processing
 Have 2 to 3 inches of water simmering or hot in
canner.
 Hot packed jars = simmering water
 Raw packed jars = warm to hot water
 Place jars on rack in canner.
 Put lid on canner with weight off or petcock
open.
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Pressure Processing
 Exhaust canner for 10 minutes.
 Close vent or petcock.
 Start counting processing times when correct
pressure is reached.
 Adjust pressure for altitude, if needed.
 Turn off heat at end of processing.
 Let pressure drop to 0 psig naturally.
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Pressure Processing
 Wait two minutes after pressure drops to 0 psig.
(For some canners, check that locks in handles are
released.)
 Remove weight or petcock.
 Open canner. Watch steam!
 Remove jars to padded surface or rack.
 Cool jars 2 to 24 hours, undisturbed.
 Check that the jars have sealed.
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MODULE 3
Canning High-Acid
Foods
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MODULE 3: Units
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Definition of a High-Acid Food
Preparing Foods for Canning
Acidifying Tomatoes
Canning High-Acid Foods
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Definition of a
High-Acid Food
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High-Acid Foods (pH < 4.6)
 All fruits, except for:
 figs
 tomatoes, and
 melons
 Rhubarb
 Fermented pickles, such as sauerkraut
 Acidified foods, such as pickles and tomatoes
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Preparing Foods for
Canning
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Selecting Fruits and Tomatoes
for Canning
 Choose firm, ripe products.
 Do not use overripe fruits.
 Gather or purchase only what you are able to
can within 2 to 3 hours.
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Washing Fruits and Tomatoes
for Canning
 Dirt contains many microorganisms hardest to
kill.
 Wash everything, even foods to be peeled.
 Use several water changes.
 Lift the food, do not soak.
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Preventing Fruit Darkening
 1 teaspoon (3000 mg) ascorbic acid added to
one gallon of water
 Commercial ascorbic acid mixture
 Heating the fruit
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Preventing Fruit Darkening
The following do not work as well:
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Citric acid solution
Lemon juice
Sugar syrup
Salt/vinegar solution
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Canning Liquids for Fruits
Sweet syrup, water or juice can be used.
Sweet syrup:
 Helps retain shape, color, and flavor of fruit. Not needed for
safety
 Mix sugar with water or juice, heat to dissolve sugar.
 Proportions of sugar to liquid given in publications.
 Up to 1/2 the sugar can be replaced by corn syrup or mild
flavored honey. (Use more corn syrup if bland.)
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Canning Liquids for Fruits
Juice Packs:
 Commercial unsweetened apple, pineapple, or
white grape juice.
 Juice can also be extracted from fruit being canned
or from the above fresh fruits.
 Extracting juice:
 Thoroughly crush ripe, sound fruit. Heat to simmering.
Strain.
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Canning Liquids for Fruits
Artificial Sweeteners:
 Add just before serving
 Saccharin-based sweeteners turn bitter
 Aspartame-based sweeteners lose flavor
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Acidifying Tomatoes
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Acidifying Tomatoes
 pH between 4.0 - 4.6 (borderline)
 Even if pressure processing, tomatoes must be
acidified.
 For Pints:
 1 tablespoon bottled lemon juice or 1/4 teaspoon citric acid
 For Quarts:
 2 tablespoon bottled lemon juice or 1/2 teaspoon. citric acid
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Acidifying Tomatoes
 Add directly to jar before filling.
 If too acid tasting, add sugar.
 Use 4 tablespoons vinegar per quart or 2
tablespoons per pint. However, flavor might be
off.
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Salt
 Salt is only used for flavor in canned tomatoes
and vegetables.
 It can be omitted because does improve the
safety of the final product.
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Canning High-Acid Foods
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Canning High-Acid Foods
 Heat canner with about six inches of water to
simmering.
 Treat new lids.
 Wash jars.
 Select and wash high quality raw product.
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Canning High-Acid Foods
 Fill jars either hot pack or cold pack:
 hot pack (food and liquid heated before filling)
 cold pack (raw food put in jar and boiling liquid
poured over it)
 Leave appropriate headspace.
 Remove air bubbles.
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Canning High-Acid Foods
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Wipe rim of jars.
Adjust lids.
Lower jars slowly into canner.
Count processing time when the water
returns to a boil.
 Remove jars to a padded surface.
 Cool away from drafts, 12 to 24 hours.
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Canning High-Acid Foods
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Check seals.
Remove screw bands.
Label.
Store.
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Headspace
 Space in the jar between the inside of the lid
and the top of the food or its liquid.
 Check canning directions for that correct
headspace for each food.
 Usually:
 1/4” for jellied fruit products
 1/2” for high-acid foods, such as fruits,
tomatoes, and pickles
 1” to 1-1/4” for low-acid foods
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Headspace
Too little:
• Food may bubble out during processing.
• Deposit on rim may prevent proper sealing.
Too much:
• Food at the top is likely to discolor.
• Jar may not seal properly, because processing
time not long enough to drive all the air from
inside the jar.
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Closing the Jars
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Remove air bubbles.
Re-adjust headspace if necessary.
Wipe jar rims.
Adjust two-piece lids, fingertip-tight.
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