Food & Nutrition: How to pressure can green beans and other low-acid foods

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By: Mary Ann Lienhart-Cross

Southern Foodways Alliance/Flickr

I know the rain has made for a challenging year for gardeners. The most popular Indiana vegetable is sweet corn, followed by tomatoes and then green beans.

Green beans, corn, meat and all other foods classified as low acid must be pressure canned. This is the serious side of food preservation science. A deadly form of a food-born poisoning is known as botulism can occur when low-acid vegetables are canned improperly.

The toxin produced by clostridium botulism causes this, and it is often fatal. This organism is extremely heat-resistant and it grows without oxygen in low-acid foods.

This deadly toxin may be produced before you see the signs of spoilage. Remember, never taste home canned non-acid foods before boiling them 10 minutes. This gives you a margin of safety in case your pressure canner’s gauge is faulty or you did not follow the pressure canning procedure exactly.

The botulinum spore that produces the toxin is killed at temperatures of 240 degrees and higher. A boiling water bath canner only reaches 212 degrees no matter how long you boil it. The botulinum spore is not killed at that temperature. To destroy the spore, you must use a pressure canner instead and reach a temperature of 240 degrees.

If you have trouble with losing liquid from the jars during pressure canning, it could be for several reasons.

The most likely reason is the food was packed raw or cold in the jars. Hot packing is preferred.

To hot pack vegetables, pre-heat the vegetables in water or by steam. Once the food is put in the jars, cover with the cooking liquid used during pre-heating or use boiling water. Cooking liquid is recommended because it may contain minerals and vitamins leached out of the food. Boiling water is recommended when cooking liquid is dark, gritty or strong-flavored, or when there isn’t enough cooking liquid to sufficiently cover the food.

Another cause of liquid loss may be due to the vegetables being packed too lightly if raw packed, or too tightly if the jar was too full.

It could also be because the pressure was lowered too rapidly for some reason, such as opening the petcock before the pressure actually reaches zero.

When pressure canning starchy food, the food may have absorbed the liquid or the pressure fluctuated during processing.

For fruits, the jars may have been too full or the jars may not have been covered with boiling water in the boiling water bath.

When you have jars that have lost liquid, besides wanting to know why, you also want to know what you should do with these jars. Check carefully if they are really sealed. If they are sealed properly, do nothing except label and store for future use. Remember, if you open the jar, you must reprocess the food again for the full length of time recommended for that food.

For current, up-to-date research-based food preservation publications visit the Purdue website.

For more recipes and tips from Purdue Extension Educator Mary Ann Lienhart-Cross, subscribe to the Food & Nutrition email newsletter.
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