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by M. Bunning, P. Kendall and E. Shackelton^* (2/22)

Quick Facts…

• All instructions in this fact sheet refer to the use of a pressure canner which is designed to reach and maintain 240° F and destroy the botulism toxin.
• Always use a tested recipe for home canned vegetables and make the necessary pressure adjustment for high elevation. At varying elevations, the processing time stays the same, but adjustment to the pounds of pressure is required.
• To ensure safety, use standard canning jars, new canning lids and maintain your canning equipment.

Preserving food at home can be a rewarding experience that provides year-round access to seasonal produce. Using tested recipes, following preparation instructions, making necessary high elevation processing adjustments, and maintaining equipment are all important for insuring the safety and quality of home preserved foods.

With renewed interest in locally-grown foods, home gardening, and food preservation, it’s important to protect yourself and your family by following safe canning methods.

• Home canned vegetables, which are low-acid foods, must be processed in a pressure canner to supply sufficient heat (240° F) to destroy botulism-causing bacteria. Failure to properly process low-acid foods in a pressure canner can allow the survival of Clostridium botulinum spores and subsequently toxin that can cause severe illness or death.
• Always use tested recipes/instructions and process at the number of pounds and specified time for your elevation. Do not take short cuts in recommended preparation or processing procedures!
• Use CSU Extension’s free Preserve Smart app/website for 24/7 access to tested home food preservation recipes and instructions for over 55 fruits and vegetables!

Equipment and Jars

• Pressure canner. Make sure your pressure canner has a tight-fitting cover, a removable rack, clean exhaust vent (or petcock) and safety valve, and an accurate pressure gauge. Replace a cracked or worn gasket to prevent water leakage and pressure loss.
  • The intense heat of pressure canning can cause the gasket to shrink over time, allowing air and steam to escape under the lid.
• Use a pressure canner that holds at least 4 quart jars.
• Electric multi-cookers and smaller stovetop pressure cookers should NOT be used for home food preservation because they cannot ensure adequate temperature and heat penetration within the jars.

Pressure canners can have one of two types of gauges:

• Weighted gauge – an instrument that is used to both indicate and regulate pressure. The weight should ‘jiggle’ several times a minute and/or keep rocking gently to maintain the desired processing pressure.
  • Weighted gauges should be cleaned before each use.
• Dial gauge – an instrument designed to indicate the pressure within the canner.
  • Dial gauges should be checked annually for accuracy which is best done in advance of canning season each year. Contact your local Extension office for more information about dial gauge testing.

Canning Jars. Discard any jars with cracks or chips since defects can prevent an airtight seal.

• Use jars designed specifically for home canning.
  • Do not use jars that are cracked or have any sort of damage (i.e. chipped) on the top edge.
• When canning vegetables, use only pint and quart jars, and then only the size recommended within the tested recipe.
  • Do not use commercial food jars (mayonnaise, pasta sauce, etc.) as they are not heat-tempered and can break easily and/or not seal properly when pressure canned.
• Wash jars in hot, soapy water and rinse well before using. Keep the jars hot until they are filled and placed in the canner to help prevent jar breakage.

Lids and Screw Bands (two-piece set). Discard any screw bands with dents or rust, since defects can prevent an airtight seal.

• Prepare new/unused flat metal lids as directed by the manufacturer.
  • Lids are designed for single-use, and should NOT be used for home canning more than once!
• Screw bands can be cleaned and used multiple times. Store carefully to prevent rusting or denting.

NOTE: One-piece home canning lids have not been researched for safe home food preservation, and are therefore not recommended.

Other Useful Canning Tools:

• Air bubble remover, plastic knife, or non-metallic spatula- used to release air bubbles from within the jar
• Canning funnel- funnel made from metal or food-grade plastic with wide, short neck for filling jars
• Headspace ruler- special graduated utensil or plastic ruler for measuring required space at the top of a filled jar
• Jar lifter- used to safely move jars to and from hot water during the canning process
• Magnetic lid wand- helps transfer metal lids to top of jars and prevent contamination
• Timer- necessary for critical timed steps throughout the canning process

Prepare Vegetables

• Select fresh, ripe vegetables for canning. The sooner from harvest to jar, the better.
• Handle produce gently to avoid bruising.
• Wash all vegetables thoroughly.
  • Avoid soaking vegetables as it may cause loss of flavor and nutrients.
• Prepare as specified in a tested recipe (size of pieces, peeled, etc.). See individual directions in Table 1.

Fill Jars

There are two approved packing methods available for safely canning vegetables. Depending on the method used, both the vegetable preparation and the approved jar size for that method need to be noted before beginning the canning process. ( For example, some vegetables cannot be safely canned in quart jars.)

• The hot-pack method is preferred for all low-acid foods, including vegetables.
  • Heat prepared vegetables in water or steam as directed by recipe before packing.
  • Loosely pack jars with prepared vegetables and cover with the boiling cooking liquid or water.
• Some vegetables can be safely processed using the raw-pack method if indicated by a tested recipe. (See individual vegetable canning directions in Table 1 to determine which method to use.)
  • Add prepared, raw vegetables to jars and cover with boiling water.
    • Firmly pack most raw vegetables (except starchy ones) into the jars.
    • Loosely pack starchy vegetables, such as corn, peas, and lima beans, because they expand during processing.

For both hot- and raw-pack:

• Salt may be added to each jar, if desired. Salt is added only for seasoning and does not help preserve the food. If salt is used, canning salt is recommended to prevent the liquid from turning cloudy. Use 1/2 tsp salt per pint/1 tsp per quart jar.
• Remove trapped air bubbles by inserting a plastic knife or non-metallic bubble remover between the food and the jar. Slowly turn the jar and move the tool up and down to allow air bubbles to escape.
• Read the directions for each vegetable for the amount of space to leave between the top of the food and the top of the jar (headspace).
  • This headspace is important to obtain a good seal and allow for expansion of the jar contents.
  • Measure headspace and add or remove liquid, as necessary.
• Wipe the jar rim with a clean damp paper towel to remove any food particles.
• Place prepared lid on the jar. Screw on the band until fingertip tight. Avoid over-tightening!
  • It is necessary for air inside the jars to be forced out from under the lids during the canning process, creating a vacuum and a proper seal.

Process in Pressure Canner

Read the manufacturer’s instructions for your pressure canner. General directions for using pressure canners are as follows:

• Add 2 to 3 inches of hot water to the canner. Keeping filled jars level, place in the canner on the rack using a jar lifter.
• Lock canner lid into place. Leave vent pipe (steam vent) uncovered, or manually open the petcock on some older models.
• Heat canner on high until water boils and generates steam that can be seen escaping through the open vent pipe or petcock. Set a timer for 10 minutes to allow the canner to continuously vent steam during this time.
• After the 10 minutes is complete, place the weight on the vent port or close the petcock. The canner will pressurize in the next 3 to 10 minutes.
• Wait to start timing the canning process (per instructions in the recipe) until the pressure reading on the dial gauge indicates the recommended pressure has been reached, or when the weighted gauge begins to jiggle or rock.
• Regulate heat under the canner to maintain a steady pressure at or slightly above the correct gauge pressure.
  • Avoid quick and large pressure variations during processing which can cause unnecessary liquid losses from jars.
  • Weighted gauges should jiggle or rock slowly throughout the canning process.
• When the timed canning process is complete, turn off the heat, carefully remove the canner from the heat if possible, and let the canner depressurize undisturbed. For safety, follow manufacturer’s guidelines.
  • Do not force-cool the canner by pouring cold water over it or manually quick-releasing steam. Forced cooling can result in breakage of the jars and/or failed seals.
• After the canner is depressurized (when the pressure gauge registers zero or the weighted gauge is no longer moving), cautiously remove the weight from the vent pipe or open the petcock.
  • Wait 10 minutes; then unfasten the lid and tilt away from you so that steam does not burn your face.

Post-Canning

• Using a jar lifter and keeping the jars level, carefully remove each jar from canner and place a few inches apart on a rack, dry towels, or newspapers. Allow jars to cool untouched, away from drafts, for a minimum of 12 but not more than 24 hours before testing seals.
  • Do not remove or re-tighten bands.
• After 12 to 24 hours, test the seals on the jar lids. Press flat metal lids at the center of the lid. Lids should be slightly concave and not move when pressed. Lids should not be buckled or damaged.

VERY IMPORTANT: Treat any jars that failed to seal as perishable (not shelf-stable).

• • The food should either be eaten immediately, refrigerated, frozen or reprocessed.
  • The processed food can safely be reprocessed if the unsealed jar is discovered within 24 hours.
    • You must repeat the entire canning process, using a new lid to ensure a safe product.
    • Be sure to check top edge of jars for nicks or cracks and replace, if necessary.
• If jars are satisfactorily sealed, remove screw bands and wipe jars with a clean, damp cloth.
  • Jars may be safely stored without bands.
  • To store with screw bands on and to avoid rusting during storage, remove, dry and re-attach bands on jars before storing.
• Label sealed jars with contents, canning method, and date.
• Store on sturdy shelving in a clean, cool, dry, dark place.

On Guard Against Foodborne Illness

Canned foods may spoil if you:

• Fail to use and follow a tested recipe/instructions
• Fail to use the proper equipment and supplies
• Fail to adhere to the proper processing time for a specific altitude/elevation
• Fail to exhaust a canner properly
• Process at lower pressure or for fewer minutes than a tested recipe specifies
• Force-cool the canner with water

Low-acid canned vegetables can contain botulism toxin without showing signs of spoilage:

• Bulging lids or leaking jars are spoilage signs for home canned foods.
• When opening a jar, look for other signs, such as spurting liquid, an off odor, or mold.
• If food looks spoiled, foams, or has an off odor during heating, discard it.

Given the challenges of high elevation food preservation and as an additional safety precaution, boil in a saucepan for 10 minutes all home-canned, low-acid vegetables and meats before tasting or serving.

• Cook 1 additional minute for each 1,000 feet above sea level (for example, boil 15 minutes at 5,000 feet).

DISPOSE OF ALL SPOILED HOME-CANNED FOOD WHERE IT WILL NOT BE EATEN BY PEOPLE , PETS OR WILDLIFE.

Table 1: Preparation methods and processing times for canning in a pressure canner

IMPORTANT: Using a boiling water bath canner is NOT a safe method for home processing of low-acid vegetables.’

• All instructions in this fact sheet refer to the use of a pressure canner which is designed to reach and maintain 240° F and destroy botulinum spores.

Critical Processing Adjustments for High Altitude/Elevation Home Canning:

• The processing times and pressures given in the table below are those recommended by the U.S. Department of Agriculture.
• DO NOT DECREASE the processing times or pressures given!
  • At varying elevations, the processing TIME stays the same, but you must make the following PRESSURE adjustments:

In a Dial Gauge Pressure Canner

• At elevations of 0-2000 feet, process at 11 pounds pressure
• At elevations of 2001-4000 feet, process at 12 pounds pressure
• At elevations of 4001-6000 feet, process at 13 pounds pressure
• At elevations of 6001-8000 feet, process at 14 pounds pressure
• At elevations of 8001-10,000 feet, process at 15 pounds pressure

In a Weighted Gauge Pressure Canner

• At elevations of 0-1000 feet, process at 10 pounds pressure
• At elevations 1001 feet and above, process at 15 pounds pressure

References and Resources

USDA Complete Guide to Home Canning. U.S. Department of Agriculture. Information Bulletin No. 539, 2009

So Easy To Preserve, 6th Edition, 2014. University of Georgia Cooperative Extension

National Center for Home Food Preservation website

Colorado State University Preserve Smart app/website

Botulism. CSU Extension https://extension.colostate.edu/topic-areas/nutrition-food-safety-health/botulism-9-305/

*M. Bunning, Colorado State University Extension food safety specialist and professor, P. Kendall, Ph.D., R.D., Colorado State University professor emeritus; and E. Shackelton, Colorado State University Extension specialist. 10/99. Revised 02/22

Colorado State University, U.S. Department of Agriculture and Colorado counties cooperating. Extension programs are available to all without discrimination. No endorsement of products mentioned is intended nor is criticism implied of products not mentioned.

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