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Author Topic: Shelf life of canned foods  (Read 2600 times)

Canuck In Denver

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Shelf life of canned foods
« on: April 25, 2009, 06:25:15 PM »

I'm posting the links then the articles, I will also post a summary at the top. These are some interesting reports and drastically change our thoughts on how long we can keep and use food in cans.

Article 1: (see August 26, 2012 note below)
Article 2:

August 26, 2012 Note:
The original link for Article 1 is no longer working. The Internet Archive has snapshots of the link from previous years, here is a link for a snapshot:[/color]

Summary Article 1:
Shelf life of 100 years for many canned goods, didn't look great or smell fresh and vitamins A and C were real low. Corn still good after 40 years, looked fresh.

Summary Article 2:
US Army finds canned meats, vegetables and jam were good after 46 years. Not more than 18 to 24 months recommended.

In other words, it won't kill you and may be better in a soup or stew, but it is food minus vitamins A and C.

FDA Study

The Canning Process:
Old Preservation Technique Goes Modern
by Dale Blumenthal

The steamboat Bertrand was heavily laden with provisions when it set out on
the Missouri River in 1865, destined for the gold mining camps in Fort
Benton, Mont. The boat snagged and swamped under the weight, sinking to the
bottom of the river. It was found a century later, under 30 feet of silt a
little north of Omaha, Neb.

Among the canned food items retrieved from the Bertrand in 1968 were brandied
peaches, oysters, plum tomatoes, honey, and mixed vegetables. In 1974,
chemists at the National Food Processors Association (NFPA) analyzed the
products for bacterial contamination and nutrient value. Although the food
had lost its fresh smell and appearance, the NFPA chemists detected no
microbial growth and determined that the foods were as safe to eat as they
had been when canned more than 100 years earlier.

The nutrient values varied depending upon the product and nutrient. NFPA
chemists Janet Dudek and Edgar Elkins report that significant amounts of
vitamins C and A were lost. But protein levels remained high, and all calcium
values "were comparable to today's products."

NFPA chemists also analyzed a 40-year-old can of corn found in the basement
of a home in California. Again, the canning process had kept the corn safe
from contaminants and from much nutrient loss. In addition, Dudek says, the
kernels looked and smelled like recently canned corn.

The canning process is a product of the Napoleonic wars. Malnutrition was
rampant among the 18th century French armed forces. As Napoleon prepared for
his Russian campaign, he searched for a new and better means of preserving
food for his troops and offered a prize of 12,000 francs to anyone who could
find one. Nicolas Appert, a Parisian candy maker, was awarded the prize in

Although the causes of food spoilage were unknown at the time, Appert was an
astute experimenter and observer. For instance, after noting that storing
wine in airtight bottles kept it from spoiling, he filled widemouth glass
bottles with food, carefully corked them, and heated them in boiling water.

The durable tin can--and the use of pottery and other metals--followed
shortly afterwards, a notion of Englishman Peter Durand. Soon, these "tinned"
foods were used to feed the British army and navy.

21 Billion Cans a Year

Canned foods are more than a relic dug from the past. They make up 12 percent
of grocery sales in the United States. More than 1,500 food products are
canned--including many that aren't available fresh in most areas, such as
elderberry, guava, mango, and about 75 different juice drinks. Consumers can
buy at least 130 different canned vegetable products--from artichokes and
asparagus to turnips and zucchini. More than a dozen kinds of beef are
canned, including beef burgers and chopped, corned and barbecued beef.

According to a recent study cosponsored by the U.S. Department of Agriculture
and NFPA, canned foods provide the same nutritional value as fresh grocery
produce and their frozen counterparts when prepared for the table. NFPA
researchers compared six vegetables in three forms: home-cooked fresh, warmed
canned, and prepared frozen.

"Levels of 13 minerals, eight vitamins, and fiber in the foods were similar,"
says Dudek. In fact, in some cases the canned product contained high levels
of some vitamins that in fresh produce are destroyed by light or exposure to

The Canning Process

Food-spoiling bacteria, yeasts and molds are naturally present in foods. To
grow, these microorganisms need moisture, a low-acid environment (acid
prevents bacterial growth), nutrients, and an appropriate (usually room)

Dennis Dignan, Ph.D., chief of FDA's food processing section, explains that
foods are preserved from food spoilage by controlling one or more of the
above factors. For instance, frozen foods are stored at temperatures too low
for microorganisms (bacteria, yeasts and molds) to grow. When foods are
dried, sufficient moisture is not available to promote growth.

It is the preservation process that distinguishes canned from other packaged
foods. During canning, the food is placed in an airtight (hermetically
sealed) container and heated to destroy microorganisms. The hermetic seal is
essential to ensure that microorganisms do not contaminate the product after
it is sterilized through heating, says Dignan. Properly canned foods can be
stored unrefrigerated indefinitely without fear of their spoiling or becoming

Canning for a New Age

Dignan also notes that foods packaged in materials other than metal cans are
considered "canned" by food processing specialists if the food undergoes the
canning preservation process. Thus, today a canned food may be packaged in a
number of other types of containers, such as glass jars, paperboard cans, and
plastics that can be formed into anything from pouches to soup bowls to
serving trays.

For example, FDA consumer safety officer Tom Gardine, holding up a small,
plastic container of half-and-half for his morning coffee, says, "This is a
canned food." He explains that the coffee creamer was heated to destroy
bacteria and sealed to prevent microorganisms from entering the sterile
container. Until it is opened, the creamer is intended to be stored on the
shelf, not in the refrigerator.

Meals for today's U.S. military come in plastic pouches--a new version of the
heavier C-rations in metal cans. Such flexible pouches aren't as popular with
American civilians as they are with Europeans. Many Americans, instead, are
buying their canned foods in plastic containers that come with a peel-off
metal top and plastic lid--ready for the microwave. Barriers (made of
sophisticated synthetic materials) that provide an airtight seal are
sandwiched in these plastic layered containers. They are used for applesauce,
pudding, and other foods that can be stored on supermarket or home shelves
for years.

Then there are containers made of new transparent plastic materials like
polyethylene terephthalate--used for peanut butter and catsup. Packages made
of paperboard layers have been designed in the shape of boxes to contain such
foods as fruit juices, tomato sauce, and even milk.

Even the tin can is changing. For years, the three-piece can (made from a
top, a bottom, and a body formed from a plate soldered into a cylinder) was
the only can around. Now there are two-piece cans, which eliminate the side
seam and one seamed end. These cans are made by feeding metal into a press
that forms the can body and one end into a single piece.

In the traditional three-piece cans, a welded side seam has replaced the
lead-soldered side seam in all but 3.7 percent of American cans, says NFPA
official Roger Coleman. The welding process uses electrodes that apply
pressure and electric current to overlapping edges at the side seam. These
new seams eliminate concern about lead leaching into metal canned foods. In
the 3.7 percent of U.S. cans where lead still is used, it is often for dry
foods (such as coffee) packaged in cans, according to Coleman. Leaching is
not a concern here.

Many imported cans, however, still bear lead-soldered side seams. To tell
whether a can has been soldered with lead, first peel back the label to
expose the seam. The edges along the joint of a lead-soldered seam will be
folded over. Silver-gray metal will be smeared on the outside of the seam. A
welded seam is flat, with a thin, dark, sharply defined line along the joint.

Turning Up the Heat

Foods with a naturally high acid content--such as tomatoes, citrus juices,
pears, and other fruits--will not support the growth of food poisoning
bacteria. In tests, when large numbers of food poisoning bacteria are added
to these foods, the bacteria die within a day. (The exact amount of time
depends upon the bacteria and amount of acidity.) Foods that have a high acid
content, therefore, do not receive as extreme a heat treatment as low-acid
foods. They are heated sufficiently to destroy bacteria, yeasts and molds
that could cause food to spoil.

Canners and food safety regulators are most concerned about foods with low
acid content, such as mushrooms, green beans, corn, and meats. The deadly
Clostridium botulinum bacterium, which causes botulism poisoning, produces a
toxin in these foods that is highly heat-resistant. The sterilization process
that destroys this bacteria also kills other bacteria that may poison or
spoil food.

Low-acid canned foods receive a high dose of heat--usually 107 degrees
Celsius (250 degrees Farenheit) for at least three minutes. (The amount of
time the food is heated, though, depends upon the size of the container and
the product.) The canned food is heated in a retort, a kind of pressure

The coffee creamer on Gardine's desk, however, was packaged differently.
Although both the half-and-half and plastic container were sterilized with
heat, they were heated separately and then brought together in a sterile
environment where the container was filled and sealed. The advantage of this
"aseptic processing," a type of canning, is that higher temperatures with
reduced heating times prevent deterioration in the quality of the food.

Aseptic processing is the "wave of the present and the future," says Gardine.
It is now used for liquids, and scientists are on the way to perfecting the
method for canning stews and chowders. However, says Gardine, because solid
foods may be more difficult to keep sterile during the filling and sealing
period, FDA is being especially cautious in approving uses for aseptic

Finessing the Attack on Food Spoilers

Another critical element in the canned food process is sealing products in
air-tight containers. It is essential that air be removed from the container
before sealing. Air could cause the can to expand during heating, perhaps
damaging the seals or seams of the container.

A telltale sign of loss of this vacuum--and a possibly contaminated
product--is a can with bulging ends. (See accompanying article.) If a seal is
not airtight, bacteria may enter the can, multiply, and contaminate the

The hermetic seal finesses the canning process. The bacteria in a food and
container are killed through heating, and at the same time new bacteria are
kept from contaminating the food.

The distinction between the canning process and food handling before
processing is an important one for food processors and regulators. Last
February, 22 students at Mississippi State University became ill after eating
omelets made with canned mushrooms imported from China. Similar outbreaks
followed in New York and Pennsylvania, affecting more than 100 people. FDA
identified the culprit as staphylococcal enterotoxin, a poison produced by
the bacteria Staphylococcus aureus.

FDA's investigation suggests that poor sanitation caused the problem, and
that the mushrooms were contaminated with staphylococcal enterotoxin even
before they were canned. The canning process did not destroy the substance
because food preservation processes are not normally designed to destroy
staphylococcal enterotoxin, a highly heat-resistant toxin.

Since this incident, FDA and the Peoples Republic of China have been working
together to determine the source of the contamination. However, FDA
authorities still are preventing mushrooms canned in China from entering the
United States. And, says Gardine, FDA is focusing attention on sanitation
procedures in imported foods.

Surpassing Napoleon

The canned food principle that won Nicolas Appert his prize of 12,000 francs
has endured over the years. What might surprise Appert, however, is how his
discovery is making food shopping and storing easier for the 20th century

Those who order coffee at fast food restaurants now also are served canned
half-and-half, which has been transported and stored without concern about
refrigeration. Hikers can take flexible pouches of canned food on backpacking
trips without having to worry about saving water to reconstitute freeze-dried
meals. And, in this society of microwave owners, Americans who don't have
time to prepare a well-balanced meal can pick up a plastic container filled
with a canned, nutritious dinner.

Dale Blumenthal is a staff writer for FDA Consumer.

How to Recognize Can Defects

"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 cans made of plastic and other materials, as well. The guidelines

Metal Cans

* 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

Plastic Cans

* any opening or non-bonding in the seal
* a break in the plastic
* a fractured lid
* a swollen package

Paperboard Cans

* a patch in the seal where bonding or adhesive is missing
* a slash or slice in the package
* a leak in a corner of the package
* a swollen package

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

Flexible Pouches

* a break in the adhesive across the width of the seal
* a slash or break in the package
* a leak at a manufactured notch used for easy opening
* a swollen package

(Taken from a chart for retailers developed by FDA and NFPA and published by
the Association of Official Analytical Chemists.)

Washington State University / US Army

Shelf Life of Canned Foods

I would like to know the age of the canned foods I purchase. Were they canned one or five years ago? Are there so many preservatives in these foods that they last years and years? Shouldn't we be able to understand those code numbers on the cans?

Codes vary from one food packer or processor to the next. Some foods have an easily recognized packing date imprinted on the top. Most, however, have their own code. There is little incentive for companies to change a system that is working well for them; especially, if they get few complaints from consumers.

Many companies have a toll-free number you can call to inquire about the code, or ask other questions. If you don't see the number on the label, remove it and see if its on the back of the label. Or, call directory assistance for toll free numbers at 1-800-555-1212. Give the company's name. This may be different from the brand name.

With one particular company, the first line of the code refers to specifics about the product. The second line, for example 31554, deals with packing. The first number, three, cites the last digit of the year it was packed, in this case 1993. The 155 uses the Julian calendar (commonly used by packers) to indicate the one-hundred and fifty-fifth day of the year. The final 4 indicated the packing shift.

All preservatives must be listed on the label. In canned foods, preservatives are used to maintain quality. The canning process keeps it safe. If a product is correctly processed, it should remain safe until opened or the seal is broken. The U.S. Army has found that canned meats, vegetables and jam were in "excellent states of preservation" after 46 years. However, long storage is not recommended. For high quality (versus safety), the broadest guideline given by the U.S.D.A. is to use high-acid canned food (fruits, tomatoes and pickled products) in 18 to 24 months, and low-acid (meats and vegetables) in two to five years.

Information developed by Carolyn Rude, Retired WSU Extension Faculty - Family Living
March 1997

« Last Edit: August 26, 2012, 11:32:29 AM by Canuck In Denver »
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