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.
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
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:
* an obvious opening underneath the double seam on the top or bottom of the
* 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.
* 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 .
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:
- 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.
- If the suspect glass jars are unsealed, open,
or leaking, detoxify (destroy the bacteria) as follows
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.
Just How Dangerous is The Botulinum
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
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..
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