It’s canning season, so this is a good time to review canning low-acid foods, especially green beans, a food that is often misused. Low acid foods are those with a pH above 4.6. The pH of the food is important because those with a pH above 4.6 allow Clostridium botulinum to grow in canned foods and produce botulinum toxin. Meat, seafood, legumes, vegetables—including green beans, corn, carrots, and zucchini—and mixtures of these foods all have a pH above 4.6. Many other foods, such as tomatoes and white-fleshed peaches, usually have a pH above 4.6.
Because Clostridium botulinum forms spores, a resistant form of the bacteria, low-acid foods should be properly handled in a pressure vessel. Spores survive boiling water temperatures of 212 degrees Fahrenheit and can only be killed at higher temperatures, around 240 degrees Fahrenheit. These temperatures can only be reached using a pressure vessel. If low-acid food is not processed in a pressure vessel, bacteria will begin to grow after the food has cooled by producing toxins in an anaerobic environment.
Alternatively, low acid foods can be acidified with the addition of acid, which inhibits the growth of bacteria.
However, the only way to know if enough acid has been added to home canned products is to use a recipe that has been researched for safety. These recipes are available through your local Extension office, the National Center for Home Food Preservation (nchfp.uga.edu), or the WSU Extension Publications website (pubs.extension.wsu.edu/consumer-food-safety).
Below are two recipes for canned green beans that have been tested for safety. The first recipe is for acidified green beans, and the second is for pressure canned green beans.
Both recipes are available on the NationalCenter for Home Food Preservation website.
4 lb. fresh, soft green or yellow beans (5 to 6 inches long)
8 cloves of garlic (optional)
1/2 cup canning or pickling salt
4 cups of white vinegar (5%)
1 teaspoon hot red pepper flakes (optional)
pint canning jars with lids
Procedure: Wash and trim the ends of the beans and cut them into 4-inch lengths. Put 1 to 2 dill heads and 1 clove of garlic, if desired, in each sterile beer jar. Arrange whole beans upright in jars, leaving 1/2-inch of top space. If necessary, trim the beans to ensure they fit properly. Combine salt, vinegar, water, and paprika (if desired). Bring it to boil. Add hot solution to beans, leaving 1/2-inch space.
Adjust lids and process in boiling water canister depending on altitude: 0-1000 ft. Five min; 1,001-6,000 feet for 10 minutes; Over 6,000 feet for 15 minutes.
An average of 14 pounds is required per 7-liter can load; An average of 9 pounds is required per 9-pint can load. Choose stuffed but soft, crunchy broad beans. Remove and discard diseased and rusty pods. Wash the beans and cut off the ends. Leave whole or cut or paste into 1-inch pieces.
For the hot pack, cover with boiling water and boil for 5 minutes. Loosely fill the jars with beans, leaving 1 inch of space. If desired, add 1 teaspoon of canning salt per liter to the jar. Coat the beans with the hot cooking liquid, leaving 1 inch of headspace.
For the raw package, fill the jars tightly with raw beans, leaving 1 inch of headspace. If desired, add 1 teaspoon of canning salt per liter to the jar. Add boiling water, leaving 1 inch of space.
Set caps and process in a pressure vessel as follows.
If you are processing green beans in a dial pressure pot, use the following processing times and pressures for your height.
Hot or raw packed beer jars: 20 minutes at 11 lbs. pressure for 0-2,000 ft altitude; 12 lb. For 2,001-4,000 feet; 13 lb. For 4,001-6,000 ft; 14 lb. for 6,001-8,000 ft.
Hot or raw packed quart jars: 20 minutes at 11 lbs. pressure for 0-2,000 ft altitude; 12 lb. For 2,001-4,000 feet; 13 lb. For 4,001-6,000 ft; 14 lb. 6,001 for 8,000 ft.
If you are processing green beans in a weighted pressure can, use the following processing times and pressures for your height.
Hot or raw packed beer jars: Process at 10 lbs for 20 minutes. if your altitude is 0-1,000 feet or 15 lbs. For altitudes above 1,000 ft.
Hot or raw packed quart jars: Process 25 minutes at 10 lbs. if your altitude is 0-1,000 feet or 15 lbs. For altitudes above 1,000 ft.
For additional information on jar selection, proper use of cans, and other canning information, please visit nchfp.uga.edu.
Smith is an assistant professor and statewide consumer food expert at Washington State University. He can be reached at [email protected] If you have a food safety question that you would like to see in this column, send your question to us at [email protected]