Canninglow-acid foods demands extra care |

Canning season is here, so it is a good time to review the canning of low-acid foods, especially green beans, a food that is commonly canned incorrectly. Low-acid foods are those with a pH above 4.6. The pH of the food is important, as those with a pH above 4.6 allow for Clostridium botulinum to grow in canned foods and produce the botulinum toxin. Meat, seafood, legumes, vegetables — including green beans, corn, carrots, and squash — and mixtures of these foods all have a pH above 4.6. Many other foods, such as tomatoes and white-fleshed peaches, often have a pH above 4.6.

Low-acid foods must be properly processed in a pressure canner because Clostridium botulinum forms spores, a resistant form of the bacteria. The spores survive boiling water temperatures of 212 degrees Fahrenheit and can only be killed at higher temperatures around 240 degrees. These temperatures can only be reached by using a pressure canner. If low-acid food is not processed in a pressure canner, bacteria will begin to grow after the food has cooled producing toxin in the oxygen-free environment.

Alternatively, low-acid foods can be acidified through the addition of acid, which prevents bacteria from growing.

However, the only way to know if enough acid has been added to home canning 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 canning 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 through the NationalCenter for Home Food Preservation website.

Pickled Dilled Beans

4 lbs. fresh, tender green or yellow beans (5 to 6 inches long)

8 to 16 heads fresh dill

8 cloves garlic (optional)

1/2 cup canning or pickling salt

4 cups white vinegar (5%)

4 cups water

1 teaspoon hot red pepper flakes (optional)

Pint canning jars with lids

Yield: About 8 pints

Procedure: Wash and trim ends from beans and cut to 4-inch lengths. In each sterile pint jar, place 1 to 2 dill heads and, if desired, 1 clove of garlic. Place whole beans upright in jars, leaving 1/2-inch headspace. Trim beans to ensure proper fit, if necessary. Combine salt, vinegar, water, and pepper flakes (if desired). Bring to a boil. Add hot solution to beans, leaving 1/2-inch headspace.

Adjust lids and process in a boiling water canner as follows, depending on altitude: 0-1,000 ft. for 5 minutes; 1,001-6,000 ft. for 10 minutes; above 6,000 ft. for 15 minutes.

Canned Green Beans

An average of 14 pounds is needed per canner load of 7 quarts; an average of 9 pounds is needed per canner load of 9 pints. Select filled but tender, crisp pods. Remove and discard diseased and rusty pods. Wash beans and trim ends. Leave whole or cut or snap into 1-inch pieces.

For hot pack, cover with boiling water and boil for 5 minutes. Fill jars loosely with beans, leaving 1-inch headspace. Add 1 teaspoon of canning salt per quart to the jar, if desired. Cover beans with hot cooking liquid, leaving 1-inch headspace.

For raw pack, fill jars tightly with raw beans, leaving 1-inch headspace. Add 1 teaspoon of canning salt per quart to the jar, if desired. Add boiling water, leaving 1-inch headspace.

Adjust lids and process in a pressure canner as follows.

If processing the green beans in a dial-gauge pressure canner, use the following process times and pressures for your altitude.

Hot- or raw-packed pint jars: 20 minutes at 11 lbs. of pressure for an altitude of 0-2,000 ft.; 12 lbs. for 2,001-4,000 ft.; 13 lbs. for 4,001-6,000 ft.; 14 lbs. for 6,001-8,000 ft.

Hot- or raw-packed quart jars: 20 minutes at 11 lbs. of pressure for an altitude of 0-2,000 ft.; 12 lbs. for 2,001-4,000 ft.; 13 lbs. for 4,001-6,000 ft.; 14 lbs. for 6,001 8,000 ft.

If processing the green beans in a weighted-gauge pressure canner, use the following process times and pressures for your altitude.

Hot- or raw-packed pint jars: Process for 20 minutes at 10 lbs. if your altitude is 0-1,000 ft., or 15 lbs. for altitudes above 1,000 ft.

Hot- or raw-packed quart jars: Process for 25 minutes at 10 lbs. if your altitude is 0-1,000 ft., or 15 lbs. for altitudes above 1,000 ft.

For additional information on selecting jars, proper use of canners, and other canning information, please visit nchfp.uga.edu.

Smith is an assistant professor and statewide consumer food specialist for Washington State University. She can be reached at food.safety@wsu.edu. If you have a food safety question you would like to see in this column, send your question to us at food.safety@wsu.edu.

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