Because vegetables are naturally low in acid, canning them requires special precautions that differ from those followed when canning high-acid fruits. Growth of micro-organisms particularly must be avoided. Some bacteria cause food spoilage, while others produce toxins that cause illness or death. For example, Clostridium botulinum is a harmless bacteria in air. However, in little or no acid, an air-free canning jar, and temperatures between 40 and 120°F, this bacteria grows and produces a deadly toxin that can cause serious damage to the central nervous system or death when eaten in even minute amounts.
Pressure processing is the only safe way to can vegetables and other non-acid foods. Boiling water produces steam. Steam under pressure raises the temperature much higher than it normally would be without pressure. To prevent botulism, the internal temperature of canned vegetables and other non-acid foods must reach 240°F. This guide provides the correct processing times and canner pressures for canning vegetables safely in New Mexico.
To prevent the risk of botulism, low-acid and tomato foods not canned according to the 1994 USDA recommendations in this guide should be boiled even if no signs of spoilage are detected. Boil food for a full 10 minutes at altitudes below 1,000 feet. Add an additional minute of boiling time for each 1,000 of feet elevation. Boiling destroys botulism toxin. If in doubt, always boil foods before tasting.
|At altitude (ft)||Boil foods (minutes)|
Select freshly harvested, tender vegetables that are free of bruises, blemishes, or signs of disease or decay. To avoid waste, prepare only the quantity of vegetables that will fill the number of jars that can fit into the canner. See the chart below for recommended quantities of food.
If desired, add 1/2 teaspoon of salt per pint or 1 teaspoon salt per quart. Salt may be omitted, as it is used only for flavor. For best results, do not use salt substitutes for canning, as heat causes some substitutes to become bitter or develop a metallic taste. Instead, add salt substitutes just before serving.
General Canning Procedures
Use regular and wide-mouth Mason jars with self-sealing lids held in place by screw-on metal bands. The bands hold the lids in place during the processing and cooling periods.
Mason jars are made from tempered glass to resist high temperatures. Jars are available in 1/2 pint, pint, 1-1/2 pint, and quart sizes. Larger jars are not recommended for home canning.
Inspect jars carefully for cracks or chips and discard faulty ones. Wash jars in hot, soapy water and rinse thoroughly or in the dishwasher. Keep jars hot in the dishwasher, a sink of hot water, or in a warm oven until they are filled.
Check metal screw bands for signs of rust or dents. Discard badly corroded or dented bands. Use only new lids and follow manufacturerÕs directions for preparing lids for canning.
Vegetables may be hot or cold packed. However, blanching for 3–5 minutes forces air from vegetables, resulting in better color and more space for food in the jar. Pack food loosely and add hot liquid, usually water. Leave a 1-inch headspace. Using a rubber or plastic spatula, slice between the food and the jar to ease out trapped air bubbles.
Use a clean, damp cloth or paper towel to wipe the rim and threads of each jar. Put on a new lid with a screw-on metal band to hold it in place; tighten comfortably. Process using a pressure canner.
Table: Estimated amounts (in pounds) of vegetables necessary for a pressure-canner load
|9 pints||7 quarts|
|Beans or peas (shelled or dried)||3-1/4||5|
|Fresh lima beans||18||28|
|Beets (without tops)||13-1/2||21|
|Corn (cream style)||20||*|
|Corn (whole kernel)||20||31-1/2|
|Peas (green, English, shelled)||20||31-1/2|
|Peppers (hot or sweet)||9||*|
|Spinach and other greens||18||28|
|1Makes 9 half-pints
2Makes 9 pints
Follow These Steps for Successful Pressure Canning
- Put 2–3 inches of hot water in the canner. Place filled jars on the rack using a jar lifter. Fasten canner lid securely.
- Leave weight off vent port or open petcock. Heat at the highest setting until steam flows from the petcock or vent port.
- Maintain high heat setting, exhaust steam 10 minutes, and then place weight on vent port or close petcock. The canner will pressurize during the next 3–5 minutes.
- Start timing the process when the pressure reading on the dial gauge indicates that 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. Quick and large pressure variations during processing may cause unnecessary liquid losses from jars. Weighted gauges on Mirro canners should jiggle about 2 or 3 times per minute. Gauges on Presto canners should rock slowly throughout the process.
- When the timed process is completed, turn off the heat, remove the canner from heat if possible, and let the canner depressurize. Do not force-cool the canner. Force cooling may result in food spoilage. Cooling the canner with cold running water or opening the vent port before the canner is fully depressurized will cause loss of liquid from jars and seal failures. Force-cooling also may warp the canner lid of older model canners, causing steam leaks. Depressurization of older models should be timed. Standard-size heavy-walled canners require about 30 minutes when loaded with pints and 45 minutes with quarts. Newer thin-walled canners cool more rapidly and are equipped with vent locks. These canners are depressurized when their vent lock piston drops to a normal position.
- After the canner is depressurized, remove the weight from the vent port or open the petcock. Wait 2 minutes, unfasten the lid, and remove it carefully. Lift the lid away from you so that the steam does not burn your face.
- Remove jars with a lifter, straight up without tipping and place on towel or cooling rack, if desired.
Do not touch lid or ring until completely cooled.
Dial gauges on pressure canners should be checked annually to make sure they are accurate.
Test for Jar Seals
Remove screw bands when jars have cooled (12–24 hours) and test for vacuum seals by these methods:
- Press the lid center with finger. If the lid springs up when released, it is not sealed.
- Tap the lid with a teaspoon. A sealed jar lid will make a ringing sound.
- Hold the jar at eye level and look across the lid. A sealed jar lid curves down slightly in the center.
Reprocessing Unsealed Jars
Remove lids from unsealed jars and discard. Check sealing surface of jar for tiny nicks or cracks. If the jar has defects, discard it and replace with another jar. If not, add a new lid and process for the same amount of time within 24 hours. Unsealed jars can be kept in the refrigerator and the food used within 3–4 days, or remove about an inch of the contents and freeze.
Storing Canned Food
Clean the outsides of sealed, cooled jars. Label with date and contents and store in a cool (50–70°F), dark, dry place away from sun, light, or dampness. Vegetable products are best if eaten within one year.
Freezing may cause food in jars to spoil if jars become unsealed. Freezing and thawing cause food to soften and lose eating quality. Protect jars from freezing by wrapping with layers of newspapers.
If Canned Food Spoils
Examine jars carefully before tasting vegetables. Check lids for a vacuum seal. NEVER taste food from an unsealed jar.
Signs of food spoilage are streaks and dried food at the top of the jar, swollen lids, broken jar seals, rising air bubbles, and any unnatural color. Other indicators include bad or unnatural odor; spurting liquid; white, blue, green, or black mold; or foaming.
Dispose of any food you suspect of being spoiled. For safety, spoiled canned food and containers may need to be detoxified before disposal. Contact your county Extension office for detoxification instructions.
All communities in New Mexico are above sea level, varying from 3,000 to 10,000 feet with differences even within a county.
Use the chart on page 7 of this guide to determine the elevation of your community and then select safe processing times for canning your vegetables. The boiling temperature of liquids is lower at higher elevations, therefore food must be processed longer or at a higher pressure at high altitudes.
Home Canning of Vegetables
Note: The following instructions are for dial gauge pressure canners. When using a pressure canner with a weighted gauge in New Mexico, use the 15-pound weight and the time periods given.
Elevations of Cities and Towns in New Mexico
|City/Town||Elevation (ft)||City/Town||Elevation (ft)|
|Bayard||5,800||Los Ranchos de Albuquerque||4,950|
|Eagle Nest||8,250||Santa Rosa||4,600|
|Grants||6,450||Truth or Consequences||4,250|
|Las Cruces||3,900||Wagon Mound||6,200|
This publication is intended for use by individuals with a basic understanding of canning procedures. For more detailed information consult the USDA Complete Guide to Home Canning, which is available through your local county Extension office.
The original author was Priscilla Grijalva, Extension Food & Nutrition Specialist. Previously revised by Martha Archuleta and Alice Jane Hendley, both Extension Food and Nutrition Specialists.
To find more resources for your business, home, or family, visit the College of Agricultural, Consumer and Environmental Sciences on the World Wide Web at aces.nmsu.edu.
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New Mexico State University is an equal opportunity/affirmative action employer and educator. NMSU and the U.S. Department of Agriculture cooperating.
Revised and electronicaly distributed August 2006, Las Cruces, NM.