Home Canning Fruits and Vegetables

In North Carolina


Angela M. Fraser, Ph.D. and Carolyn J. Lackey, Ph.D.
Department of Family and Consumer Sciences

How Canning Preserves Food

To can means to heat process food in a glass jar with a lid in place. Processing kills microorganisms -- bacteria, yeasts, and molds -- that contaminate food and cause food spoilage and/or foodborne illness. Processing can be done in a water bath canner or a pressure canner, depending on the food's acidity.

Acid foods (all fruits except unacidified figs) can be safely processed in a water bath canner. Acidified tomatoes and figs can also be safely processed in a water bath canner. Microorganisms in or on acid foods are easily killed at 212 degrees F (the temperature of boiling water). Low-acid foods (vegetables and tomatoes and figs that are not acidified) must be processed in a pressure canner. The bacteria that produces botulinum toxin cannot grow in acid foods but can grow in low acid foods. These bacteria (Clostridium botulinum) have spores that survive hours of boiling water temperature. However, these spores are destroyed within a reasonable time at 240oF (the temperature reached inside a pressure canner set at 10 pounds pressure).

If low-acid food is processed in a water bath canner, botulinum spores on the food will survive. In the absence of air, a condition found inside a jar after processing, the spores become living bacteria. As the bacteria grow, they form toxin. Eating even a drop of this potent toxin can be fatal to humans and animals. Over 70% of the cases of botulism have been caused by low-acid foods that were improperly canned at home.

To make sure your home canned foods are safe, carefully follow the canning instructions in this bulletin. Process acid foods in a water bath canner and low-acid foods in a pressure canner. Never process any foods in a conventional oven, microwave oven, steamer or dishwasher, as these methods do not kill microorganisms that cause food spoilage and/or foodborne illness.

Recommended Canning Equipment

Before each canning season, assemble and examine all canning equipment.

Canning jars. Use only standard canning jars (also called Mason jars) with the manufacturer's name printed on the side. These jars can withstand the temperature extremes of canning. And, the sealing edge is smooth and flat so lids will seal properly.

Never use commercial jars, such as mayonnaise and pickle jars, for home canning. These jars are not very resistant to temperature extremes; they break easily. Also, lids may not seal on these jars because their sealing edge may be rounded rather than flat. Finally, the neck of the jar may be so short that the screw band will not hold the lid firmly in place during processing.

Canning jars must be in perfect condition. Check all jars, new and used, for hairline cracks, chips or nicks on the sealing edge. Such defects can result in breakage or failure to seal.

Canning lids. The only safe way to seal a canning jar is with a two-piece canning lid. The set consists of a flat metal lid and a screw band. The lid has a sealing compound around the edge and is enameled on the under side to prevent food from reacting with the metal. The screw band holds the lid in place during processing. A vacuum seal forms during cooling, after the jar is removed from the canner. Screw bands that are in good condition may be reused, but always use new lids. Do not use screw bands that are bent or badly rusted.

Two types of canners. Use a water bath canner to process acid foods. A water bath canner is a large deep kettle that has a cover and a rack to hold jars. You can also use a big, covered pot that is deep enough to allow water to extend 1 to 2 inches over the tops of the jars with enough room for the water to boil briskly. Also add a rack to keep the jars off the bottom of the pot.

Use a pressure canner to process low acid foods. A pressure canner is a deep, heavy kettle that has a rack on the bottom for jars to stand on. It also has a tight-fitting lid with a gasket, and a pressure gauge. The gasket keeps steam from leaking out around the cover. If the gasket is worn, stretched, or hardened, replace it. There are two types of pressure measuring gauges, dial gauge and weighted gauge.

A dial gauge has a needle that moves along a numbered scale to indicate the pressure inside the canner. Each year check the dial gauge, old or new, for accuracy and during the canning season if heavily used. Call your extension agent, Family and Consumer Sciences, to find out where testing can be done.

A weighted gauge fits over the air vent tube. It permits pressure in the canner to rise to the desired point and then releases excess steam by "jiggling" or "rocking" to keep the pressure from going higher. Weighted gauges do not need testing for accuracy, but they do need to be kept clean. Check the vent tube to be sure it hasn't been bent or damaged during use.

Getting Canning Equipment Ready

Wash canning jars in a dishwasher or in hot soapy water, and rinse well. Keep jars hot by leaving them in the dishwasher or hot water until you are ready to fill them. Jars do not need to be sterilized, as this will be accomplished during processing. Wash and rinse canning lids and screw bands. Follow the manufacturer's directions for preparing lids. They may need to be boiled in water for a few minutes before use.

Preparing Fruits and Vegetables For Processing

Select high quality, unblemished fruits and vegetables for canning. Canning will not improve quality. Can them as soon as possible after harvesting. If you must hold foods before canning, keep them in the refrigerator. If you buy fruits or vegetables to can, get them fresh from local farmer's markets, roadside stands or pick-your-own farms.

Thoroughly wash fruits and vegetables before canning even if they will be peeled. Garden soil contains bacteria. NOTE: Potatoes must be peeled before canning. Potato skins contain a high bacteria count increasing the chance of botulinum toxin formation.

Wash by scrubbing with a vegetable brush and rinsing thoroughly. Or, if more practical, soak in water for several minutes. Lift out of the water so the soil that has been washed off won't settle back on the food. Peel, pit, and/or slice only as much food as you can process at one time.

Some fruits and vegetables (apples, apricots, nectarines, peaches, pears and potatoes) darken when cut. To prevent darkening, keep raw, prepared produce in a solution of 1 teaspoon ascorbic acid to one gallon of cold water. Check among the canners' supplies in the supermarket to get this product.

Sugar and Salt

Sugar helps retain the color, shape and texture of canned fruits. Sugar is usually added as a syrup. To make syrup, pour 4 cups of water into a saucepan and add: Heat until the sugar dissolves. Make 1 to 1-1/2 cups of syrup for each quart of fruit. Up to half the sugar used in making syrup can be replaced with light corn syrup or mild-flavored honey. Fruits also can be safely canned without sugar. Pack the fruit in extracted juice, in juice from another fruit (such as bottled apple juice, pineapple juice, or white grape juice) or in water. Salt may be added to vegetables and tomatoes before canning. Since its only function is flavor, it can be safely omitted. Canning fruits and vegetables without adding sugar or salt does not affect processing times or microbiological safety.

Packing Instructions

The two methods of packing food into canning jars are raw pack and hot pack. Raw pack is packing raw, prepared food into clean, hot jars and then adding hot liquid. Fruits and most vegetables need to be packed tightly because they will shrink during processing. However, raw corn, lima beans, and peas should be packed loosely, as they will expand. For hot pack, heat prepared food to boiling or partially cook it. It should be packed loosely while boiling hot into clean, hot jars. Hot pack takes more time but has been found to result in higher quality canned foods.

For either packing method, pack acid foods including acidified tomatoes and acidified figs to within 1/2 inch of the top of the jar. Low acid foods to within 1 inch of the top of the jar.

After food is packed into jars, wipe the jar rims clean. Put on the lid with the sealing compound next to the jar rim. Screw the band down firmly so that it is hand-tight. Do not use a jar wrench to tighten screw bands. There must be enough "give" for air to escape from the jars during processing. Process food promptly after packing it into jars and adjusting lids. Processing times are given for pints and quarts. If you are using half pint jars, use processing times for pints. For one-and-one-half pint jars, use processing times for quarts. Fruit juices are the only product that may be canned in half-gallon jars.

Canning at Altitudes Above 1,000 Feet

If you live at an altitude of more than 1,000 feet, you will need to modify the processing time for acid foods and the pounds pressure you use to process low-acid foods. The processing instructions presented in this bulletin are for altitudes of 0-1000 feet.

To determine your altitude, contact the North Carolina Geological Survey Office. Their address is: 512 North Salisbury Street, P.O. Box 27687, Raleigh, NC 27611. Their telephone number is 919-733-2423. After determining your altitude, your local extension center can help you to determine changes you need to make to your canning instructions.

Processing in a Water Bath Canner

Use a water bath canner to process acidified tomatoes, acidified figs and all other fruits. A pressure canner can be used to process acid foods but the quality will not be as good.
  1. Fill the canner half full with water; then cover and heat. For raw-packed food, have the water hot but not boiling. For hot-packed food, have the water boiling.
  2. Using a jar lifter, place jars filled with food on the rack in the canner. If necessary, add boiling water to bring water 1 to 2 inches over the tops of the jars. Do not pour boiling water directly on jars. Cover.
  3. When water comes to a rolling boil, start counting the processing time. Keep water at a rolling boil for the entire processing time. Add more boiling water to keep water 1 to 2 inches above jars.
  4. As soon as the processing time is up, use a jar lifter to remove jars from canner. If liquid has boiled out of the jars during processing, do not open them to add more. Do not retighten screw bands, even if they are noticeably loose.

Processing in a Pressure Canner

If you live at an altitude of 0-1000 feet, you can process foods in a weighted gauge pressure canner at 10 pounds pressure. If you are using a dial gauge pressure canner, use 11 pounds pressure. If you live at an altitude more than 2,000 feet you need to increase the pounds pressure at which you process foods. These increases are not given in this bulletin. Contact your county extension center to get this information. If tomato products are acidified, they can be safely processed in a water bath canner. If not, they must be processed in a pressure canner.

Here are some pointers for using a pressure canner:

  1. Pour 2 or 3 inches of water in the bottom of the canner and heat to boiling.
  2. Set jars on the rack in the canner. If you have two layers of jars in the canner, use a rack between them and stagger the second layer.
  3. Fasten the canner cover securely so steam cannot escape except through the vent.
  4. Once steam pours steadily from vent, let it escape for 10 minutes to drive all air from the canner. During processing, the canner must be filled with steam, not air, since it is steam that reaches the desired temperature of 240 F.
  5. a. If the canner has a weighted gauge, start counting the processing time when it jiggles or rocks. The target pressure for this type of canner is 10 pounds pressure. Adjust heat so that gauge jiggles 2 or 3 times a minute or maintains a slow, steady, rocking motion.

  6. b. If the canner has a dial gauge, bring pressure up quickly to 8 pounds, then adjust the heat to maintain 11 pounds pressure. Start counting the processing time when the gauge registers 11 pounds pressure.
  7. When the processing time is up, turn off the burner. (If you are using a coal or wood stove, remove canner from heat.) Let the pressure in the canner drop to zero by itself. This may take 45 minutes in a 16-quart canner filled with jars and almost an hour in a 22-quart canner. If the vent is opened before the pressure drops to zero or if the cooling is rushed by running cold water over the canner, liquid will be lost from the jars.
  8. When the pressure has dropped to zero, open the vent or remove the weighted gauge. (With a weighted gauge canner, pressure is completely reduced if no steam escapes when the gauge is nudged or tilted. If steam spurts out, pressure is not yet down.)
  9. Remove canner cover carefully, tilting it away from your face so that the rising steam cannot burn your face or hands.
  10. Remove jars from canner. If liquid boiled out of jars during processing, do not open jars to add more liquid. Do not retighten screw bands, even if they are noticeably loose.
  11. Place hot jars upright to cool on a towel or rack. Leave space between them so air can circulate. Keep jars out of drafts.

Check Seals

Vacuum seals form as the jars cool. When jars are cool (12 to 24 hours after processing), check the seals. If the lid is depressed or concave and will not move when pressed, it is sealed. If sealed, carefully remove screw bands. If a band sticks, loosen it by covering it for a moment with a hot, damp cloth. Bands left on jars during storage may rust, making later removal difficult.

If you find an unsealed jar, do one of the following:

The eating quality of twice-processed food may be poor. If more than 24 hours have gone by since processing, throw out the food. It might be unsafe to eat.

Label and Store Sealed Jars

Label sealed jars with the processing date. Store them in a cool, dry, dark place. Properly stored canned foods will retain their quality for at least a year. Never store canned foods near hot pipes, a range, a furnace, or in direct sunlight because they lose quality.

If stored in a cold place, protect from freezing by wrapping the jars in newspaper or covering them with a blanket. Canned foods that do freeze may be used as long as freezing does not break the seal. However, they may not be as tasty as properly stored canned foods.

If canned foods are kept in a damp place, lids may rust.

Signs of Spoilage

Before using always check canned foods for signs of spoilage -- leakage, bulging lids, or loss of seal. Bulging or loss of seal indicates gas formation inside the jar. Upon opening the jar, look for spurting liquid. After opening, check for gassiness, cloudy liquid, disagreeable odor, or mold. Never taste food that shows any sign of spoilage. Throw it out; it might be unsafe to eat. Furthermore, never feed this food to animals; it could make them sick.

Cloudy liquid may be a sign of spoilage or be due to minerals in hard water or starch from overripe vegetables. If liquid is cloudy, check for other signs of spoilage. If there are not other signs of spoilage, boil the food. Do not eat any food that foams or has a disagreeable odor during heating.

Always boil home-canned, low-acid foods for 10 minutes before tasting. Do not use this method to make improperly processed food "safe." If enough bacteria is present (due to improper processing), boiling for ten minutes might not destroy the toxin.

Black deposits on the underside of a lid are not a sign of spoilage. The under side of canning lids is coated with enamel. If there are imperfections, such as tiny scratches or pinholes in the enamel, natural compounds in food can react with the metal in the lid to form harmless brown or black deposits.

For more information call the Extension Agent, Family and Consumer Sciences, in your county. The Cooperative Extension Service is usually listed in the telephone directory under county offices. 


Processing Directions for Canning Acidified Tomatoes, Acidified Figs and Other Fruits

All processing times are given for processing in a water bath canner. Pack foods listed below to within ½ inch of the top of the jar. Source of instructions is the USDA Complete Guide to Home Canning, 1995.
 
Water Bath Process Water Bath Process
PRODUCT PROCEDURES
PACK STYLE Pints (minutes) Quarts (minutes)
Apples Wash, peel, core, and slice apples. Drain and rinse. Cook and pack. Cover with hot liquid or hot syrup. Hot only 20 20
Applesauce Prepare sauce and make sweetened or unsweetened. Hot only 15 20
Figs* Wash and drain. Do not peel or remove stems. Cover with water and boil for 2 minutes then drain. Gently boil figs in light syrup for 5 minutes. Hot only 45 50
Peaches Wash, peel and pit. Slice if desired. Drain and rinse. Pack cooked or raw. Cover with hot liquid or boiling-hot syrup. Hot or Raw 20 - Hot
25 - Raw
25 - Hot
30 - Raw
Pears Tree-ripened pears may have a coarse, gritty texture when canned. So, pickpears when they are full size but still firm and green. Hold for 2 weeks in the refrigerator then ripen them at room temperature before canning. Wash, peel, halve, and core pears. Cut into quarters if desired. Drain and rinse. Cook and pack. Cover with hot liquid or boiling-hot syrup. Hot only 20 25
Plums To can whole, prick skins in several places with table fork to prevent splitting. Freestone varieties may be halved and pitted. Pack cooked or raw. Cover with hot liquid or hot syrup. Hot or Raw 20 25
Tomatoes, acidified and packed in water To loosen skins, dip into boiling water for about 1/2 minute, then dip quickly into cold water. Peel and core. Leave small tomatoes whole. Halve or quarter larger tomatoes. Pack cooked or raw.  Hot or Raw 40 45
Tomatoes, acidified* and packed in tomato juice Follow directions above except cover with hot tomato juice. Hot or Raw 85 85
Tomatoes, acidified* and packed raw without added liquid Follow directions above except when packing press tomatoes in the jars until spaces between them fill with juice. Raw only 85 85 
Tomato juice, acidified* Quickly cut 1 pound of fruit into quarters -- to prevent juice from separating. Heat immediately to boiling while crushing. Continue to slowly add and crush freshly cut tomato quarters to the boiling mixture. Simmer 5 minutes after you add all pieces. Hot only 35 40
Tomato sauce, acidified* Prepare and press as for making tomato juice. Simmer until sauce reaches desired consistency. Boil until volume reduced by one-third for thin sauce; one-fourth for thick sauce. Hot only 35 40

* Add 2 tablespoons bottle lemon juice per quart or 1 tablespoon per pint; or add ½ teaspoon citric acid per quart or ¼ teaspoon per pint to the jars.


DIRECTIONS FOR CANNING VEGETABLES

Vegetables and tomatoes and figs that are not acidified are low-acid foods. All processing times are given for processing in a weighted-gauge pressure canner at 10 pounds pressure at an altitude of 0-1000 feet and in a dial-gauge pressure canner at 11 pounds pressure (at an altitude of 0-2000 feet). Source of instructions is the USDA Complete Guide to Home Canning, 1995.
 
Pressure Process Pressure Process
PRODUCT PROCEDURES
PACK STYLE Pints (minutes) Quarts (minutes)
Beans, lima Shell and wash. For both raw and hot pack, pack beans loosely into clean, hot jars. Cover with boiling hot water. Hot or Raw 40 50
Beets Sort beets for size. Cut off beet tops, leaving an inch of stem. Leave only 1 inch of root attached. Scrub beets well. Cover with boiling water until skins slip off easily, 15 to 25 minutes depending on size. Peel and trim off top and root. Leave baby beets whole. Cut medium or large beets into 1/2-inch cubes or slices. Cook and pack immediately. Cover with fresh hot water. Hot 30 35
Corn, whole kernel Husk corn and remove silk. Wash. Cut corn from cob at about 3/4 of the depth of the kernel. CAUTION: Do not scrape cobs. Pack cooked or raw. Cover with cooking liquid or fresh boiling water. Sweet corn sometimes darkens during processing due to caramelization of sugar. The sweeter the corn, the more likely it is to darken. Although the dark color is unattractive, the corn is safe to eat. Hot or Raw 55 85 
Corn, cream style Follow instructions above except for cream style corn, scrape remaining corn from cobs and add to jar. To each quart of corn and scrapings, add two cups of boiling water. Heat to boiling. Add ½ teaspoon salt to each jar, if desired.  Hot only 85 ---
Greens Remove tough stems and midribs. Place about 2-½ pounds greens in a cheese cloth bag and steam about 3 to 5 minutes or until well wilted. Pack loosely and cover with boiling water. Hot only 70 90
Green beans Wash and trim ends. Leave whole or cut or snap into 1-inch pieces. Hot or Raw 20 25
Mixed Vegetables 6 cups sliced carrots
6 cups cut, whole kernel sweet corn
6 cups cut green beans
6 cups shelled lima beans
4 cups whole or crushed tomatoes
4 cups diced zucchini
Wash and drain all vegetables except zucchini. Wash, trim and slice or cube zucchini. Boil for 5 minutes and pack. Cover with cooking liquid.
Hot only 75 90
Peas, green Shell and wash. Cook and pack. Cover with cooking liquid or fresh boiling water. Hot or Raw 40 40
Potatoes, sweet Use small to medium potatoes. Can pieces or whole within 1 to 2 months after harvest. Wash and boil or steam (15 to 20 min). Remove skins. Cut into uniform pieces. CAUTION: Do not mash or puree pieces. Pack and cover with fresh boiling water or syrup. Hot only 65 90
Pumpkin, cubed Wash pumpkin, remove seeds, and peel. Cut into 1-inch cubes. Cook and pack. Cover with cooking liquid. 
CAUTION: Only cubed pumpkin or winter squash is recommended for home canning. If desired, mash just before serving or using in recipes. Do not can mashed pumpkin or winter squash, as the product may be too thick to ensure adequate heat penetration during processing.
Hot only 55 90
Squash, winter cubed Follow method for pumpkin, cubed. Hot only 55 90
Tomatoes, whole or halved packed in water Wash tomatoes. Dip in boiling water for 30 to 60 seconds until skins split; then dip in cold water. For raw pack cover with water and pack. For hot pack, boil gently for 5 minutes then pack. Hot or Raw 10 10

Sources for additional canning instructions:


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