Whether you frequent the farmers market, peruse seasonal produce at the grocery store or tend a garden of your own, even well planned harvests can yield an abundance of food that seems to come at once. Canning can make the fruits (and vegetables) of your labors last beyond the growing season, but without proper handling and know-how, some food preserving projects can turn into a hotbed for bacteria and foodborne illness. Learn how to preserve the harvest safely.
There are two methods for canning foods. In the “raw pack” method, jars are filled with raw produce and covered with a hot liquid or syrup before being processed. In the “hot-pack” method, foods are cooked first, then ladled into jars. Both methods require heat processing to kill pathogens and denaturing enzymes that would otherwise break down the foods and by creating a vacuum that protects the food from air
Because the hot-pack method is more effective in removing air, it preserves the nutritional quality, appearance, flavor and texture of foods better than the raw-pack method. This is particularly true of foods that are processed in a boiling-water canner as opposed to a pressure canner.
Tips for Home Canning
- Start with the freshest possible produce.
- Sterilize jars and lids as outlined in the procedures. (Running jars through the dishwasher will not sanitize.)
- Only new, unused canning lids will ensure a proper seal. Glass jars can be reused.
- Don’t improvise. With canning, it is crucial to follow food selection, preparation, filling and processing instructions to the letter, and only use recipes from trusted sources that have been properly developed and tested.
- Store at 50-70°F. Before opening a jar, look for signs of leaks and check that the lid is firmly sealed and concave. Once open, visible signs of spoilage or unexpected odors means throw it away.
Food Safety Issues
The biggest safety concern with home canning is C. botulinim, a bacterium that produces a toxin so lethal that even a single taste of contaminated food can be deadly. While botulism poisoning is fairly rare (the Centers for Disease Control and Prevention has documented around 400 cases in the last 50 years), 92% of these cases were caused by home canned foods. Botulinum spores are naturally prevalent in the environment, but they only become dangerous when conditions favor their growth: a moist, room temperature, airless, low-acid environment—precisely the conditions created in many canned goods.
Safe canning is not difficult, but it requires attention to detail. The U.S. Department of Agriculture’s Complete Guide to Home Canning, which includes detailed procedures, safety instructions and hundreds of recipes for everything from pickled asparagus to tomatillo salsa to green tomato pie filling, is available free at http://uga.edu.nchfp or in print for $18 at www.extension.purdue.edu/store. For those trying canning for the first time, start with less risky acid foods such as pickles, jams and preserves.
Acid versus Low-Acid Foods
Controlling the pH of canned goods is vitally important. Foods with a pH of 4.6 or lower are considered “acid foods” (most fruits, including tomatoes). Anything higher is a “low-acid food” (most vegetables, meats and other foods), requires special processing and can be acidified with vinegar, citric acid or lemon juice.
Using the Correct Processing Equipment
Acid foods can be safely processed in a boiling water canner because the low pH blocks the growth of botulinim spores. Low-acid foods (if they are not acidified with vinegar or another low pH solution) must be processed in a pressure canner. Repeat: a boiling water canner cannot be used when a recipe calls for a pressure canner!
Processing at Altitude
Altitude can affect processing time and pressure. When processing foods at altitudes above 1,000 feet, stick with recipes that have altitude-specific directions.
Storing Canned Goods
For best quality, consume acid foods such as fruit, pickles and tomato sauce within 18 months. Other vegetables are best consumed within two to three years. Store canned foods at 50-70°F.
USDA’s Complete Guide to Home Canning 2009
Ball Blue Book of Home Preserving