Food Preservation Facts or Myths? (FN1427, Reviewed July 2021)

Food preservation guidelines have changed through time. Test your knowledge of current food preservation recommendations by deciding if these statements are facts or myths. See the answers and explanations on the back.

Julie Garden-Robinson, Ph.D., R.D., L.R.D. Food and Nutrition Specialist

Availability: Web only

1. Fact or myth? Old church cookbooks have great canning recipes you will want to use.

2. Fact or myth? As long as you boil the jars of canned vegetables long enough, you will have a safe end product.

3. Fact or myth? Vegetables, meats and most mixtures of foods should be canned only in a pressure canner.

4. Fact or myth? Canning in your oven is a safe, convenient way to seal jars.

5. Fact or myth? You can invent your own salsa recipe and can it as long as you process it in a water-bath canner.

6. Fact or myth? Acid, such as lemon juice or citric acid, should be added to all tomatoes prior to canning.

7. Fact or myth? Most vegetables do not require heat blanching prior to freezing.

8. Fact or myth? You can expect high-quality food when you freeze foods in plastic containers that previously held whipped topping or margarine.

9. Fact or myth? You can use glass mayonnaise jars to can food, such as peach sauce, in a boiling water-bath canner.

10. Fact or myth? Paraffin wax provides an excellent seal on jelly and jam jars.

11. Fact or myth? Pickles are so acidic that they do not need to be processed in a boiling water-bath canner.

12. Fact or myth? Screw bands should be tightened “fingertip tight” prior to canning.

Answers and Explanations

1. Myth. Old church cookbooks often provide outdated and unsafe canning recipes.

U.S. Department of Agriculture canning guidelines underwent a major overhaul in 1994, and in 2006, canning guidelines were reviewed and revised. Follow only current research-tested canning recipes, such as those from USDA/Extension or Ball.

2. Myth. Unless you process canned foods properly, you could put yourself at risk for botulism, a potentially fatal form of foodborne illness. Clostridium botulinum spores can grow and produce a toxin in low-acid foods in sealed cans or jars. Boiling jars at 212 degrees will not kill this organism or its spores.

3. Fact. The acidity (or pH) of a food determines how foods should be canned. Low-acid foods such as these must be processed in a pressure canner:

  • Vegetables (except when acidified)
  • Meats
  • Poultry
  • Seafood
  • Soups
  • Mixtures of acidic and low-acid foods

4. Myth. Canning in an oven is not safe. This method can be extremely dangerous for low-acid foods.

5. Myth. If you invent your own salsa recipe, you can freeze it. Follow salsa formulations exactly and measure/weigh ingredients carefully.

6. Fact. Tomato varieties vary in the amount of acid they contain depending on variety and growing season. For safety, tomatoes to be canned in a water-bath canner or a pressure canner should be acidified with one of the following:

  • Add 2 tablespoons of bottled lemon juice per quart (1 tablespoon per pint)
  • Add ½ teaspoon of citric acid per quart (¼ teaspoon per pint)

7. Myth. For best quality, vegetables should be heat-treated (or blanched) in boiling water for the recommended length of time. Blanching inactivates enzymes (small proteins that regulate processes). Without blanching, undesirable flavor, texture and color changes can occur.

8. Myth. Using these types of containers can result in freezer burn or dehydration. Freezer burn is a quality issue, not a safety issue. You may not want to eat freezer-burned food because of changes in the color, texture and flavor.

9. Fact (kind of). They are safe to use, but Mason-type jars are the best choice for canning. Expect more seal failures and potential breakage when reusing commercial glass jars. Mayo jars have a narrower sealing surface and are tempered less than Mason jars.

10. Myth. Paraffin wax does not provide an air-tight seal. Spoilage (mold growth) can occur. Use two-piece, self-sealing lids on jams and jellies.

11. Myth. Many molds, yeasts and some bacteria survive in acidic environments. To inactivate molds, yeast and bacteria, process pickles in a water-bath canner for the recommended time.

12. Fact. Just use your fingertips – not your muscles – to tighten screw bands. Overtightening can lead to seal failures. Prepare lids as directed on the package. Do not reuse lids. You can reuse screw bands.

For more information about food preservation, visit these websites: 

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