Most of us have a can of beans or peaches tucked in the back of the pantry that's been there longer than we'd like to admit. Fresh fruit would have rotted long ago. Yet the can still looks fine. What's the secret that keeps canned food from going bad?
Here's the short answer. Canning seals food inside an airtight container and then heats it enough to kill the microbes that cause spoilage. With no germs left inside and no way for new ones to get in, there's nothing to make the food rot. Canned food typically lasts one to five years, and under the right conditions, much longer.
Seal It, Then Heat It
The order matters. Food is packed into a can or jar, sealed, and then sterilized with heat. Doing it in that order means both the container and the food inside end up germ-free together, with nothing able to sneak in afterward.
The seal is crucial. Modern cans use a double seam, invented in 1888, that folds and presses the lid and can body together into a tight, airtight joint. If a can isn't sealed properly, bacteria can get in and the food can spoil. That's one reason a bulging or leaking can is a red flag.
Some foods need extra care. The spores of the germ that causes botulism can only be destroyed at temperatures above the boiling point of water. So low-acid foods, like most vegetables, are canned under pressure to reach those higher temperatures. If you have questions about home canning safety, it's worth following trusted guidelines, and talk to your doctor if you ever suspect food poisoning.
A Prize From Napoleon's Era
Canning began with a contest. Shortly before the Napoleonic Wars, the French government offered 12,000 francs to anyone who could find a cheap, reliable way to preserve food for its army.
Nicolas Appert, a French confectioner and brewer, noticed that food cooked inside a sealed jar didn't spoil unless the seal leaked. He developed a method of sealing food in glass jars and won the prize in 1810. Amazingly, nobody knew why it worked. It would be about 50 more years before Louis Pasteur showed that microbes cause food to spoil.
From Glass Jars to Tin Cans
Glass was heavy and fragile, so inventors soon switched to cans. A patent for food in tin cans was filed in Britain in 1810, and by 1817 one British company was selling canned meat to the army and navy. Early cans were handmade, and cooking food inside them could take six hours, so canned goods were too pricey for ordinary families at first.
Here's a funny wrinkle: can openers weren't invented until about 30 years after the tin can. Soldiers cut cans open with bayonets or smashed them with rocks.
The 109-Year-Old Cans
In 1865, a steamboat called the Bertrand sank in the Missouri River. In 1974, canned food recovered from the wreck was tested. Its appearance, smell, and vitamin content had faded, but there was no trace of microbial growth, and the food was judged still safe to eat after 109 years.
Canned food holds up well nutritionally too. A 1997 study found canned fruits and vegetables were about as rich in fiber and vitamins as fresh or frozen ones, and sometimes richer. So that dusty can of peaches in your pantry might be a better friend than you thought.
