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Extension specialist: Carefully follow instructions to preserve foods safely

A common mistake people make when canning is not following proper processing times. Image: Christie Clancy
A common mistake people make when canning is not following proper processing times. Image: Christie Clancy

UNIVERSITY PARK, Pa. -- Whether you picked a basket of tomatoes from your own garden or purchased a peck of cucumbers from your favorite farm stand, you can continue to enjoy fresh fruits and vegetables throughout the year by properly preserving them.

But when it comes to the quality and safety of these foods, there are a few important precautions that must be taken during preservation, according to Martin Bucknavage, a food-safety extension specialist in Penn State's College of Agricultural Sciences.

The easiest way to preserve most fruits and vegetables is to freeze them, he noted. However, it is important to know whether you will need to blanch your produce item before freezing.

"Blanching is a process that destroys enzymes that are naturally present in fruits and vegetables," he said. "If you do not blanch the food item, the enzymes will cause deterioration of the plant tissue, rendering it mushy upon thawing."

Blanching can be done by dipping the item into boiling water or by steaming it. Generally, blanching by steam will take twice as long as dipping it in boiling water, but the item will pick up less moisture. For example, green beans should be water blanched for three minutes and steam blanched for five minutes.

It is critical to follow a proven, standardized recipe when preserving foods, Bucknavage explained. "Preservation recipes were developed to ensure the product will not become unsafe or spoil during storage," he said. "You can find these recipes on university extension websites, such as Penn State's, as well as on the Ball Home Canning website.  

"Some recipes will allow for small modifications, but making bigger changes, such as changing the amount of vinegar to be added, are highly discouraged. The acidification process is an important step in controlling Clostridium botulinum, the causative agent of botulism."

A common mistake that Bucknavage sees people making is that they do not follow proper processing times.

Bucknavage stressed one very important point about preserving low-acid foods such as green beans, corn, beets and soups: To prevent botulism, use a pressure canner.

"In low acid foods, there is insufficient acidity to prevent the growth of Clostridium botulinum, so we have to eliminate this organism through heat," he said. "This organism forms a heat resistant spore that survives boiling, so higher temperatures are needed. These temperatures can be achieved only in a pressure canner."

Too many people still process low-acid foods such as green beans in a boiling water bath, Bucknavage said, which is risky because Clostridium spores may survive the process and then grow in the canned food.

Numerous conversations with home canners have convinced Bucknavage that there is still widespread reluctance to using a pressure canner, even though safety devices in modern pressure canners greatly reduce the risk of personal injury.

"Of course, it is important that you consider replacing your canner if it does not have safety devices on it," he said. "Old pressure canners often do not have pressure relief devices."

A common mistake that Bucknavage sees people making is that they do not follow proper processing times.

In addition to following the recipe, home canners should be sure to follow the proper processing time. If the recipe specifies that the product must be heated before putting it in the jar, then it must be heated. If the recipe calls for the jars to be processed for 30 minutes, then it must be processed for at least 30 minutes at the correct temperature or pressure. 

"Recently, a Washington man contracted botulism from improperly processed, canned elk meat. He survived, but suffered for a month on a hospital ventilator," Bucknavage said. "He thought he could speed the process by reducing the process time. Unfortunately, the process was not long enough to rid the meat of botulinum spores, and the first jar of meat he ate was contaminated."

Botulism rarely happens, but when it does it can be devastating, Bucknavage said.

"It is easy enough to prevent. Just follow the proper recipes and process times for the products you are preserving. Know when you need to use a pressure canner, and if you don't want to pressure can, you usually can freeze the item."

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