Canning Errors

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Food Poisoning

Growth of the bacterium Clostridium botulinum in canned food may cause botulism—a deadly form of food poisoning. These bacteria exist either as spores or as vegetative cells. The spores, which are comparable to plant seeds, can survive harmlessly in soil and water for many years. When ideal conditions exist for growth, the spores produce vegetative cells which multiply rapidly and may produce a deadly toxin within three to four days of growth in an environment consisting of:

  • a moist, low-acid food,
  • a temperature between 40°F and 120°F, and
  • less than 2 percent oxygen.

Botulinum spores are on most fresh food surfaces. Because they grow only in the absence of air, they are harmless on fresh foods.

Most bacteria, yeasts, and molds are difficult to remove from food surfaces. Washing fresh food reduces their numbers only slightly. Peeling root crops, underground stem crops, and tomatoes reduces their numbers greatly. Blanching also helps, but the vital controls are the method of canning and use of the recommended research_based processing times found in the publications of this home-canning series. These processing times ensure destruction of the largest expected number of heat-resistant microorganisms in home-canned foods.

What Causes Botulism?

Botulism spores are resistant to heat -- even from boiling water -- and thrive in a moist, oxygen-free environment. As botulism spores reproduce, they generate one of the most extraordinarily powerful poisons on earth: one teaspoon-worth is sufficient to kill 100,000 people. Improper home canning creates the perfect environment in which to grow the botulism toxin. Also, because food contaminated by botulism may very well look and smell normal, there is often no warning. That is why home canning must be done properly with extreme care. 

 How To Identify Spoiled Canned Food

"Never eat food from a tin can with bulging ends" was a maxim many grew up with. Bulging was one of several clues that might indicate contamination of food packaged in metal cans. Guidelines have been adapted for recognizing defects in canned goods:
  • Metal Cans * an obvious opening underneath the double seam on the top or bottom of the can * a can with bulging ends * a fracture in the double seam * a pinhole or puncture in the body of the can * an unwelded portion of the side seam * a leak from anywhere in the can.
  • Glass Jars * a pop-top that does not pop when opened (indicating loss of the vacuum) * a damaged seal * a crack in the glass of the jar .

 

How Dispose of Spoiled Canned Food

Never taste food from a jar with an unsealed lid or food that shows signs of spoilage. As you use jars of food, examine the lid for tightness and vacuum; lids with concave centers have good seals.

Before opening the jar, examine the contents for rising gas bubbles, and unnatural color. While opening the jar, smell for unnatural odors and look for spurting liquid and mold growth (white, blue, or green) on the top food surface and underside of lid.

Spoiled acidic food should be discarded in a place where it will not be eaten by humans or pets.

Treat all jars and cans of spoiled low-acid foods, including tomatoes, as though they contain botulinum toxin and handle in one of two ways:

  1. If suspect glass jars are still sealed, place them in a heavy garbage bag. Close the bag, and place it in a regular trash container or bury it in a landfill.

  2. If the suspect glass jars are unsealed, open, or leaking, detoxify (destroy the bacteria) as follows before disposal:

Carefully place the containers and lids on their sides in an eight-quart or larger pan. Wash your hands thoroughly. Carefully add water to the pan until it is at least one inch above the containers. Avoid splashing the water. Place a lid on the pan, and heat the water to boiling. Boil 30 minutes to ensure that you have destroyed all toxins. Cool and discard the lids and food in the trash, or bury in soil. Sanitize all counters, containers, and equipment that may have touched the food or containers--don't forget the can opener, your clothing, and hands. Place any sponges or washcloths used in the cleanup in a plastic bag and discard.

Menu


Food Poisoning
Ensuring Safe Foods
What Causes Botulism 
How Dangerous is Botulism
Identifying Spoiled Food  
Disposing of Contaminated Foods
Controlling Botulism

Just How Dangerous is The Botulinum Toxin?

In low-acid foods, essentially all non-fruits, the botulinum organism can grow and have a great time if it is not eliminated in the canning process. Canning requires pressure cooking with the proper canner at 10 pounds pressure to kill the organism and make food safe." In addition to the danger of botulism, any food that is improperly handled is subject to growth of other food poisoning bacteria such as salmonella, E. coli, and listeria, all of which can cause serious sickness or death.

As little as two billionths of a gram of Botulinum Toxin can cause symptoms. Put another way, if you stick your finger into a suspicious can of food and lick it to see if it tastes bad, you may have ingested enough toxin to kill you.

I don't want to scare you out of home canning. Just remember that if you don't follow the rules you put yourself at risk and the consequences are potentially very serious.

Controlling Botulism

Whether food should be processed in a pressure canner or boiling-water canner to control botulism bacteria depends 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 these bacteria. Acid foods contain enough acidity to block their growth or to destroy them rapidly when heated. The term “pH” is a measure of acidity; the lower its value, the more acidic the food. The acidity level in foods can be increased by adding lemon juice, citric acid, or vinegar.

Low-acid foods have pH values higher than 4.6. They include red meats, seafood, poultry, milk, and all fresh vegetables except for most tomatoes. Most products that are mixtures of low-acid and acid foods also have pH values above 4.6 unless their ingredients include enough lemon juice, citric acid, or vinegar to make them acid foods. Acid foods have a pH of 4.6 or lower. They include fruits, pickles, sauerkraut, jams, jellies, marmalade, and fruit butters.

Although tomatoes usually are considered an acid food, some are now known to have pH values slightly above 4.6. Figs also have pH values slightly above 4.6. Therefore, if they are to be canned as acid foods, these products must be acidified to a pH of 4.6 or lower with lemon juice or citric acid. Properly acidified tomatoes and figs are acid foods and can be safely processed in a boiling-water canner.

Botulinum spores are very hard to destroy at boiling-water temperatures; the higher the canner temperature, the more easily they are destroyed. Therefore, all low-acid foods should be sterilized at temperatures of 240°F to 250°F, attainable with pressure canners operated at 10 to 15 PSIG. (PSIG means pounds per square inch of pressure as measured by a gauge.) At these temperatures, the time needed to destroy bacteria in low-acid canned foods ranges from 20 to 100 minutes. The exact time depends on the kind of food being canned, the way it is packed into jars, and the size of jars, as well as the altitude where you live..

Errors In Temperatures
Can Occur Because:

 Internal canner temperatures are lower at higher altitudes. To correct this error, canners must be operated at the increased pressures specified for appropriate altitude ranges.

Air trapped in a canner lowers the temperature obtained at 5, 10 or 15 pounds of pressure and results in under processing. The highest volume of air trapped in a canner occurs in processing raw-packed foods in dial-gauge canners. These canners do not vent air during processing. To be safe, all types of pressure canners MUST be vented 10 minutes before they are pressurized.