Although the family can consume a fair amount of the garden bounty before it spoils, home canning that food is a great way to preserve that summer-fresh taste all year long.
The key to canning is safety! Jars of improperly canned low-acid foods and meats can contain the deadly botulism toxin without showing signs of spoilage. The spores of Clostridium botulinum bacteria, which are found naturally in soil, are heat resistant
There are three different safe methods for home canners to use: boiling water, atmospheric steam, and pressure canning. Whether food is high acid or low acid indicates what type of processing method should be used. Generally, high-acid foods can be safely canned in a water bath or atmospheric steam canner. Low-acid foods must be processed in a pressure canner.
Boiling water and atmospheric steam canners are used for processing naturally acidic or properly acidified foods with rated pH values of 4.6 or below, conditions which do not support the growth of the spores. Most fruits have naturally high levels of acid. While tomatoes have some natural acids, they are borderline between high and low acids. They need commercially bottled lemon juice, citric acid, or vinegar (labeled 5 percent acidity) to increase their acidity for safe food processing. Many vinegars are not 5%, meaning they are not strong enough to preserve foods safely. You must check the container to ensure the correct acidity. Fermented foods, such as sauerkraut, and foods to which a sufficient amount of vinegar is added, as in pickled vegetables, are also canned as high-acid foods. Jams and jellies are high-acid foods unless low-acid vegetables, such as peppers, are added.
Maintaining a temperature of 212°F for the time specified in an approved recipe is adequate to destroy molds, yeasts, enzymes, and some bacteria. At higher altitudes, water boils at lower temperatures, making it necessary to process foods longer. Hours in a boiling water canner won’t kill the spores from Clostridium botulinum. Left alive after canning, they’ll eventually germinate into actively growing bacterial cells that produce a deadly human toxin when consumed. The bacteria like the conditions inside closed jars of low-acid foods sitting at room temperature, so they must be killed for safe storage during a high heat pressure canning process.
Pressure canning is the only safe method of canning low-acid foods (those with a pH of more than 4.6). Low-acid foods must be processed at 240°F using a pressure canner, and this temperature can only be reached in a pressure canner. Low-acid foods include all low-acid vegetables, meats, poultry, and seafood.
There are two types of pressure canners available, including a dial gauge and a weighted gauge. Dial gauge canners use a dial to show the pressure inside the canner, and the weighted gauge style has weights on the open vents that let the canner choose 5, 10, or 15 pounds of pressure for processing.
It is essential to have the dial gauge tested for accuracy before each canning season or after accidentally dropping or banging it. Contact your local Extension office for information regarding dial gauge testing. Weighted gauges do not need testing.
The USDA recommends using a pressure canner/cooker that can hold at least four quart-size jars, standing upright on a rack inside the canner. The lid must be able to be closed. Smaller cookers and electronic multicookers are not recommended for home canning use!
Ensure all pressure canner parts are in good condition, including the rubber gasket, if needed, which should be flexible and soft, not brittle, sticky, or cracked. Be sure to check for debris in the openings of any small pipes or vent ports.
Those new to pressure canning or simply needing more information can follow recipes and procedures outlined at the National Center for Home Food Preservation to ensure food safety. Other trusted resources include Ball® and the University of Wyoming Extension Food & Nutrition Website at https://uwyoextension.org/uwnutrition/category/food-preservation. For safety’s sake, please update your methods!
It is necessary to make adjustments to the pressure at altitudes above 1,000 feet. If you are canning at an altitude over 1000 feet, follow the altitude adjustments given in the recipe resource you are using. In Wyoming, the altitude ranges from 3,100 feet to 13,800 feet above sea level, so you must adjust the recipe for altitude.
Recipes published before 2015 should be checked against a current, reliable resource for safety. Not all recipes found on the web or in other publications are scientifically tested.
Using up-to-date canning instructions is vital. Scientific knowledge and equipment have changed since earlier generations were canning foods at home. Use procedures that have been scientifically tested to ensure safe, high-quality canned products.
Canning can be intimidating at first, but do not let that prevent you from using this preservation method. Follow current USDA processing methods and be sure to adjust canning times for your altitude. Have fun canning!
Written by Vicki Hayman, MS, University of Wyoming Extension Nutrition and Food Safety Educator
Sources: