Department of Family and Consumer Sciences

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Preserving Nature’s BountyPrinciples of Home Canning

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How Canning Preserves Foods

• Control growth of undesirable microorganisms– Bacteria– Molds– Yeasts

• Control activity of enzymes• Control

– Reactions with oxygen– Moisture Loss

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Proper Canning Practices

• Carefully selecting and washing fresh food

• Peeling some fresh foods• Hot packing many foods• Adding acids (lemon juice or

vinegar) to some foods

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Proper Canning Practices

• Using acceptable jars and self-sealing lids

• Processing jars in a boiling-water or pressure canner for the correct time

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Not recommended• Open-kettle

canning• Microwave

canning• Dishwasher

canning• Oven canning

Open-kettle canning

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Temperatures• 2400 F – low acid foods

– Pressure canning– Kills bacterial spores

• 2120 F – high acid foods– Water-bath canning– Kills molds, yeasts and some

bacteria

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Temperatures• 0o F

– Freezing– Temporarily stops growth of

microbes, does not kill

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How Canning Works• Air is driven from the jar or

can• A vacuum seal is formed• Prevents air (with

microorganisms) from getting back into food

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The Effect of Altitude• Affects how long food is processed; water boils at lower

temperatures as altitude increases• For water-bath canning: Add time for higher altitudes• For pressure-canning: Add pressure for higher altitudes• Tennessee Valley varies from 2000-2500 feet

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Use Mason Jars

• ½ pint• Pint• Quart• ½ gallon

(for high-acid juices only)

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Use Two-Piece Lids

•Rings•Seals (cannot be reused)

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Jars to Avoid• Old-style jars

– Wire bails and zinc lids– Cannot be fitted and sealed

• Commercial jars– Mayonnaise, peanut butter,

etc.– Narrower sealing surface– Less tempered (will

break in pressure canners)

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Raw or Hot Pack• Raw-Pack

– Pack jars with uncooked product

• Hot-Pack – Pack jars with cooked product– Maintains better color over time– Removes more air

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Control Headspace• Space between product

and lid– ¼ inch for jams and jellies– ½ inch for fruits and tomatoes– 1 to 1 ¼ inch for foods processed in

pressure canners

• Too much space, takes too long to drive out air

• Too little space, may not seal

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Filling Jars• Fill clean jars with

food• Remove excess air• Wipe rims• Apply lids and

rings• Tighten fingertip

tight

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General Principles• Follow tested recipes• Do not alter ingredients• Use water-bath canner for high

acid foods, pickles, jellies• Use pressure canner for low

acid foods

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For more information on preserving foods safely, contact Pat Whitaker,Extension Agent Family & Consumer Sciences Rutherford CountyDeveloped by Janie Burney, PhD, RDProfessor, Family and Consumer Sciences