Sometimes you get just what you need from your garden harvest. However, most of the time, you end up with more tomatoes, zucchinis and cucumbers than you can eat. Iowa State University of Extension nutrition and health specialist Rachel Wall helps guide you through preserving your garden bounty for later enjoyment.
Q: How do I safely can food at home?
A: Canning is the process by which food is placed in a jar and heated to a temperature that destroys microorganisms. The heat also inactivates enzymes that lead to spoilage. When done properly, canning will remove the air from the jar so a vacuum seal is formed.
Clostridium botulism is a serious foodborne illness that can result from eating improperly canned foods. It is important to always follow research-tested recipes and instructions. These recipes have been tested to ensure Clostridium botulinum spores are killed when heated long enough at a specific temperature. Recipes developed before 1988 are not recommended.
The acidity of the food is important in determining which type of canning is needed. Processing times are determined by acidity, size of the jar, thickness of the food, and the elevation at which canning is done.
Acidity: The term “pH” is a measure of acidity; the lower the value, the more acidic the food. The acidity level in foods can be increased by adding vinegar, lemon juice, or citric acid. Acid foods have a pH of 4.6 or lower. Low-acid foods have pH values higher than 4.6.
The amount and method of heat processing used depends primarily on the acidity in the food. Acidity may be natural, as in most fruits, or added, as in pickled food. Low-acid canned foods contain too little acidity to prevent the growth of heat-resistant bacteria. Acid foods contain enough acidity to block their growth or destroy them more rapidly when heated.
Boiling water bath: This type of canning is recommended as a safe method for processing acid foods. Most fruits are considered acid foods, however, tomatoes, figs, and Asian pears require lemon juice or citric acid to be added to them to have a pH of 4.6 or lower. Jams, jellies, conserves, grape and apple juice, and some pickled products are also considered acid foods.
A boiling water bath canner can be any pot deep enough to hold a rack and canning jars and still have room to cover the jars with 1 to 2 inches of water. It must have a lid. The temperature reaches 212 degrees at sea level and processing times will be different for different food items being canned.
Pressure canning: If food has a pH of 4.6 or higher, it is considered low-acid and must be processed in a pressure canner. Meats, poultry, fish, seafood, milk and all fresh vegetables, except for most tomatoes, are low-acid foods with pH values above 4.6. Their natural acid level is too low to prevent growth of heat-resistant, spore-forming, bacteria common on these foods. Therefore, all low-acid foods should be processed at temperatures of 240 degrees to 250 degrees, attainable with pressure canners operated at 10 to 15 pounds pressure.
Elevation: Because of the lower boiling point of water at high altitude, ISU Extension recommends increasing the processing time 5 minutes if more than 1,000 feet above sea level when using a boiling water bath. When pressure canning, make the following adjustments for dial gauge (sea level: 10 pounds psi; 1,001 to 2,000 feet: 11 psig) and weighted gauge (use 15 pounds for all altitudes above 1,000 feet) pressure canners.
Most counties in southeast Iowa do not need to adjust for altitude when canning. Additional information on home food preservation, including a map of elevations of Iowa counties can be found at www.extension.iastate.edu/families/preserve-resources.
Garden classes, 10 a.m. every Saturday at NewBo City Market, 1100 Third St. SE, Cedar Rapids. Meet at the Learning Garden. Free.
Prairie Walk, 6:30 to 8 p.m. Tuesday at 5791 Michael Dr., Cedar Rapids. Linn County Master Gardener Dave Mahlke will talk about the types of prairie flowers seen on this 1/3 acre restored prairie. Free. Register at (319) 377-9839 Ext. 323 or firstname.lastname@example.org.
Salsa-making workshop, 1 to 5 p.m. July 31 at the Johnson County Extension office in Iowa City. Learn more about hot water bath canning and knife skills. Register by Wednesday. To participate, enroll in “Preserve the Taste of Summer” at www.ucs.iastate.edu/mnet/preservation/home.html by enrolling at the “silver level” and complete required online lessons. Register one week prior at (319) 768-8777 or email@example.com.
Leave it to the Leaves: A cottage-in-the Meadow Gardens Workshop, 2:30 to 5:30 p.m. Saturday at Hwy. 220 in South Amana. Cost: $5. Register by Wednesday at firstname.lastname@example.org. Larry Rettig will show the impact leaves create in your garden. Food Preservation 101, 2 to 4 p.m. Aug. 1 at the Jones County Extension Office, 800 N. Maple St., Monticello. Learn the basics in canning, freezing, dehydrating, and knife skills with Rachel Wall. Free. Register: (319) 768-8777 or email@example.com one week in advance.
Questions on gardening, land use or local foods? Contact Michelle Kenyon Brown, community ag programs manager at Linn County Extension, firstname.lastname@example.org.