Safe Practices for Preservation

August 18, 2010

As summer fruit and vegetable season comes to an end, you still have time and a fun opportunity to enjoy these delicious and nutritious foods throughout the year by canning them at home.

As summer fruit and vegetable season comes to an end, you still have time and a fun opportunity to enjoy these delicious and nutritious foods throughout the year by canning them at home.

The popularity of sourcing local ingredients, coupled with the increase nationally in the number of farmers’ markets providing fresh options, has ensured that preserving or putting food by is back in favor. Last fall, canning and freezing supplies experienced the highest annual growth rate for a supermarket sales category as tracked by The Nielsen Co. Between October 2008 and October 2009, sales of home-preserving products by the manufacturer of Ball and Kerr canning jars rose 12 percent.

Fresh preserving provides a number of great benefits that are relevant to today’s lifestyles. From sustainable lifestyles to lowering grocery bills, the reasons why people can today are different from the reasons why people canned foods years ago. Food safety is critical when preserving food in this fashion - whether you’re pickling cucumbers, making jam or storing summer tomatoes for the winter.

Canning is based on scientific principle. It’s important to remember there is little room for changes when it comes to canning recipes. The smallest change in the recipe or process can turn a beautiful preserve into a bacteria-filled disaster. Canning deals with microorganisms that spoil the output with a choice combination of several techniques: lowering available water, removing oxygen, applying heat and relying on natural acids or adding acids.

Whether food should be processed in a pressure canner or boiling-water canner to control botulinum bacteria depends on the acidity of the food. Acidity may be natural, as in most fruits, or added, as in pickled food. Low-acid canned foods are not acidic enough to prevent the growth of these bacteria. Low-acid foods have pH values higher than 4.6. They include red meats, seafood, poultry, milk and all fresh vegetables except for most tomatoes. Most mixtures of low-acid and acid foods also have pH values above 4.6 unless their recipes include enough lemon juice, citric acid or vinegar to make them acid foods. Acid foods have a pH of 4.6 or lower. They include fruits, pickles, sauerkraut, jams, jellies, marmalades and fruit butters.

The best way to ensure great results is to begin with good-quality fresh foods suitable for canning. Quality varies among varieties of fruits and vegetables. Many County Extension offices can recommend varieties best suited for canning. Follow USDA guidelines for canning to ensure the best possible results:

• Obtain high-vacuum jars and airtight jar seals.
• Use only high-quality foods that are at the proper maturity and are free of diseases and bruises.
• Use the hot-pack method, especially with acid foods to be processed in boiling water.
• Don’t unnecessarily expose prepared foods to air. Can them as soon as possible.
• While preparing the canner load of jars, keep peeled, halved, quartered, sliced or diced apples, apricots, nectarines, peaches and pears in a solution of 3 grams ascorbic acid to 1 gallon of cold water. This procedure is also useful in maintaining the natural color of mushrooms and potatoes, and for preventing stem-end discoloration in cherries and grapes. You can get ascorbic acid in several forms: pure powdered form (1 teaspoon = 3 grams); vitamin C tablets (500-milligram variety, crush six tablets per 1 gallon of water); and commercially prepared mixes of ascorbic and citric acid.
• Fill hot foods into jars and adjust headspace as specified in recipes.
• Tighten screw bands securely, but if you are especially strong, not as tightly as possible.
• Process and cool jars.
• Store the jars in a relatively cool, dark place, preferably between 50 degrees and 70 degrees Fahrenheit.
• Can no more food than you will use within a year.

The National Center for Home Food Preservation warns home canners not to can green beans and other vegetables in boiling water instead of under pressure. In the past two years, there have been at least three cases of botulism poisoning from improperly processed home-canned green beans. If you’ve never canned before, consider taking a class at a local County Extension office. The 1973 book “Putting Food By” - now in its fifth edition - is a classic if you’re considering entering the world of home canning. Additionally, a free online course is offered by the national association, called “Preserving Food at Home: A Self-Study".