Home Canning Safety Tips


One of the special treats of summer is the abundance of fresh fruits and vegetables ready for the eating. Whether you grow your own, or have access to locally grown produce, you may be considering home canning as a way to preserve your favorite foods. If done correctly, canning can be a safe and economical way to preserve quality homegrown foods.

Vegetables start losing vitamins as soon as they are harvested. More than 50% of the vitamins are lost if the produce isn’t cooled or preserved within 2 to 3 days of being harvested. Refrigerated produce (such as produce found at the local supermarket) will lose more than half of the vitamins after 1 to 2 weeks. Even though the heating process involved in canning destroys a proportion of the heat-sensitive vitamins found in vegetables (vitamins A and C, riboflavin, and thiamin), freshly canned vegetables will be equally, if not more nutritious than the produce found at the local supermarket.


The nutritive and economic advantages of home canning can be lost if foods are not canned safely. The purpose of canning is to preserve the quality of fresh food. There are several reasons why foods spoil:

  • Growth of microorganisms such as yeasts, molds, and bacteria
  • Activity of enzymes found in food
  • Moisture loss
  • Reactions with oxygen

Proper canning will prevent microorganism growth, destroy food enzymes, remove oxygen, and maintain moisture content. If safe home-canning procedures are not followed one or more of these processes will be compromised resulting in food spoilage.


Bacteria grow in different conditions. Depending on the particular bacteria, they can grow at different temperatures, on low- or high-acid foods, and with or without oxygen. Although the majority of bacteria are destroyed by heat, some produce spores that can only be destroyed by temperatures above the boiling point (212 degrees F). Clostridium botulinum is one such bacterium. When the conditions are right (moist, low-acid food, temperature between 40 and 120 degrees F, and less than 2 percent oxygen), the Clostridium botulinum spores will produce the deadly botulism toxin. Because these spores can grow on low-acid foods, low-acid foods must be heated under pressure to reach a temperature (240 degrees F) high enough to destroy the spores. Most bacteria prefer low-acid foods. Following is a list of low- and high-acid foods.

Low-acid foods:

Beans, shelled
Beans, snap
Spinach and greens

High-acid foods:

Fruit juices
Pickled beets
Tomato juice

* Some varieties of tomatoes have a slightly lower acidity, therefore it is recommended to add lemon juice or citric acid to properly acidify the tomatoes before canning.

Molds and yeasts grow well on high-acid foods, but are destroyed at temperatures between 140 and 190 degree F.

Two canning processing methods:

  • Boiling water method – used to can high-acid foods. In this method jars are completely covered with boiling water for a specific amount of time. The time depends on the type of food. Reliable canning manuals will give the times required for different foods.
  • Pressure canner method – used to can low-acid foods. In this method jars are heated under pressure to a temperature of 240 degrees F. This process ensures the destruction ofClostridium botulinum spores.

Salt, sugar, and vinegar are frequently added to home-canned products. These ingredients also help inhibit microorganism growth.

Other suggestions for safe canning:

  • Use quality fresh foods – pick fruits and vegetables that are fresh and void of any bruising or mold. Process vegetables within 6 to 12 hours of harvesting. It is best to let fruit ripen 1 to 2 days between harvesting and canning.
  • Use jars and lids specifically made for canning – jars should be void of any cracks or chips to ensure a proper seal. Do not re-use lids. Inspect lids for dents or gaps that may prevent proper sealing. Follow manufacturer’s instructions for processing.
  • Process for correct time and temperature/pressure – it is essential to process the canned goods for the correct time and temperature (boiling water bath method) and pressure (pressure canner method). Refer to a canning guide for the correct canning time and temperature/pressure for the food being processed.
  • Adjust for altitude – adjustments for altitudes of 1,000 above sea level or higher need to be made for both canning methods. Time needs to be increased 5 minutes for altitudes between 1,000 and 6,000 feet for the boiling water bath method. If using the pressure canner method, process at 12 pounds pressure for altitudes between 2,000 and 4,000 feet and at 13 pounds pressure for altitudes between 4,000 and 6,000 feet.

Canning can be an inexpensive and fun process if done properly. Plan ahead for the foods you’re anticipating to can, this will ensure you have the correct process and equipment ready to go when the fruits and vegetables are harvested.

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