All summer long, you worked hard preparing the soil, planting seeds, removing weeds and watering. Now, hopefully, your garden has rewarded you with a bumper crop. If so, one way to preserve your excess fresh fruits and vegetables is by home canning. With proper planning and equipment, home canning is relatively straightforward. Although preparation methods and processing times differ for various fruits and vegetables, the basic principles of canning are similar.
Equipment: Vegetables are low in acid and must be processed in a steam pressure canner at a pressure needed to reach 240 degrees Fahrenheit to supply enough heat to destroy bacteria that cause botulism. At Colorado’s high altitude, the pressure needed is 10 pounds plus 1/2 pound for every 1,000 feet above sea level. For example, at 5,000 feet, vegetables need to be canned at 12.5 pounds pressure or higher. Before you begin, make sure your pressure canner has a tight-fitting cover, clean exhaust vent and safety valve, and an accurate pressure gauge.
Fruits are canned using a boiling water bath. Any big metal container may be used as a boiling water bath canner if it is deep enough (at least 4-5 inches deeper than the height of the jars), has a tight fitting cover and a wire or wooden rack. At altitude, water-bath processing times will need to be increased to compensate for the lower temperature of boiling water.
Whether you’re canning in a boiling water bath or pressure canner, standard canning jars are recommended. Commercial food jars that are not heat-tempered, such as mayonnaise jars, break easily and may not seal properly. Throw away any jars with cracks, chips, dents or rust. Always wash jars in hot, soapy water and rinse well before using. Prepare lids according to manufacturer instructions.
Preparing produce: Select fresh, young, tender vegetables and fresh, firm fruits for canning. Wash produce thoroughly, whether or not it will be pared, because dirt contains some of the bacteria that’s hardest to kill.
Filling and processing jars: The hot-pack method is recommended for all low-acid vegetables, although the raw-pack method is acceptable for some vegetables. Fruits can be packed into jars raw, or preheated and packed hot. Follow directions specific for the type of produce regarding the amount of headspace to leave. Air bubbles should be removed by sliding a nonmetallic spatula between the food and the sides of the jar. When processing vegetables in a pressure canner, follow the manufacturer’s directions with adjustments made as needed for altitude. Instructions for using a water bath are provided in the Canning Fruits fact sheet available from Colorado State University Cooperative Extension.
The day after: Test the seals on the jar lids by pressing the flat metal lids at the center of the lid. Lids should be slightly concave and should not move. Remove screw bands. Label sealed jars with contents, canning method and date. Store in a cool, dry, dark place. Food in unsealed jars should be treated as fresh and eaten immediately, refrigerated, frozen or fully reprocessed.
Be on guard against spoilage: Bulging lids or leaking jars are signs of spoilage. When you open a jar, look for other signs, such as spurting liquid, an off odor, or mold. Dispose of all spoiled canned food in a place where it will not be eaten by people or pets. Be aware that low-acid canned vegetables can contain botulism toxin without showing signs of spoilage. As a safety precaution, boil all home-canned vegetables in a saucepan for 10 minutes, plus 1 minute for each 1,000 feet above sea level before tasting. Spinach and corn should be boiled for 20 minutes.
For more information about canning fruits and vegetables, including specific preparation methods and processing times, call your local cooperative extension office and request fact sheets 9.348 Canning Vegetables, 9.347 Canning Fruits, and 9.341 Canning Tomatoes and Tomato Products, or visit the Web at www.ext.colostate.edu.
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by Pat Kendall, Ph.D., R.D., Food Science and Human Nutrition Specialist, Colorado State University, Cooperative Extension