AUBURN UNIVERSITY, Ala.—Many gardeners enjoy canning homegrown fruits and vegetables for later use. It is important to use fresh foods, can soon after picking and follow recommended processing times and procedures. This will help ensure wonderful, fresh-tasting fruits and vegetables to enjoy during the fall and winter months.
Use Fresh Produce
Angela Treadaway, an Alabama Extension regional agent of food safety and quality, said using fresh produce helps ensure quality while home canning.
“Use fruit and vegetable varieties that are well-suited to canning,” Treadaway said. “After harvest, the food should be washed and examined carefully. Old, diseased or moldy food should be thrown away. Trim away any small diseased lesions or spots from food that is in otherwise good condition.”
Follow Processing Procedures
People should process most vegetables within six to 12 hours after picking. Allow apricots, nectarines, peaches, pears and plums to ripen one or more days between harvest and canning. Spread produce in a single layer on a clean, dry surface to ripen more evenly. If you have to delay the canning of fresh produce, keep it in the refrigerator or in a cool, dark place.
Treadaway said it is important to follow processing time guidelines. Proper canning practices:
- remove oxygen from food tissues
- destroy enzymes
- prevent the growth of bacteria, yeast and molds
- help form a vacuum in jars
Good vacuums form tight seals that keep liquid in, and air and microorganisms out. If people do not follow proper home canning practices, chances increase for the survival of Clostridium botulinum, the bacteria that causes botulism. Botulism is a deadly form of food poisoning. These bacteria exist either as spores or vegetative cells. Under ideal conditions, the deadly toxin can be produced in three or four days. Ideal conditions include a moist, low-acid food, a temperature between 40°F and 120°F and less than two percent oxygen.
The acidity, or pH, of a food determines whether it should be processed in a pressure cooker or a water-bath canner. Acid blocks the growth of Clostridium botulinum bacteria and destroys them more rapidly when heated. The acid may be natural—as with most fruits—or it may be added, as in pickled foods. High acid foods are not at risk for botulinum growth. However, people must destroy botulinum spores in low-acid foods with high heat of 240 degrees, which only a pressure canner can do. Water bath canning should never be used for canning any type of vegetable except for pickled items and sauerkraut
Use Acidic Foods
Acid foods with a pH or 4.6 or lower, can be canned in a water-bath canner. They include most fruits and some varieties of tomatoes. Tomatoes, however, do require the addition of ascorbic acid to assure the correct acidity.
Low acid foods have a higher pH higher than 4.6 and must be canned in a pressure canner. They include meats and all fresh vegetables. Mixing low-acid foods with high-acid foods does not always lower the pH enough to keep it safe. When making items like salsa, please follow a USDA tested recipe to assure accuracy and correct ratio of high to low acid. Usually the addition of vinegar or lemon juice is necessary.
Process low-acid foods at 240°F. Only pressure canners operated at 10 to 15 pounds per square inch of pressure can reach this temperature range. At these temperatures, the time needed to destroy bacteria in low-acid foods ranges from 20 to 100 minutes. The exact time depends on the food, packing method and jar size.
“Always follow time, temperature and pressure recommendations carefully,” Treadaway said. “It is best to use USDA tested recipes which can be found on the internet at the National Home Food Preservation Website. Home-canned foods will be free of spoilage if they are properly prepared and processed, the lids are sealed to form a high vacuum and the foods are stored at temperatures between 50°F and 70°F.
Maintain Good Flavor and Color
To maintain good color and flavor during processing and storage, do the following:
- Use only high quality, disease-and bruise free foods in the proper stage of maturity.
- Wash foods thoroughly and trim away small damaged areas.
- After preparing foods for canning, protect them from much exposure to light, heat and air. Can them as soon as possible.
- Fill clean, hot jars with hot food, leaving the amount of headspace specified in the recipes.
- Remove air bubbles from filled jars and wipe rims with a clean, damp, cloth before adjusting lids.
- Use recommended self-sealing lids and screw bands or rings.
- After canning, store sealed jars in a cool, dark, dry place, preferably between 50°F and 70°
For more information about home canning safety and food preservation, contact your county Extension office to find out about classes near you. Read more about safe canning methods in Alabama Extension’s Wise Methods of Canning Vegetables.