The History of Home Canning and What Safety Requires Today

Where canning came from, why it worked before anyone knew why, and the modern rules that are not optional.

Canning preserves food by sealing it in a container and heating it enough to stop spoilage. The method was invented by Nicolas Appert in France, who was awarded a prize for it in 1810, and home canning took off after John Landis Mason patented his screw-top glass jar in 1858. For most of that history, people canned successfully without understanding the biology behind it.

Today we do understand it, and that understanding comes with rules that must be followed exactly. The most important is this: low-acid foods such as vegetables and meats must be processed in a pressure canner, not a boiling-water bath, because only a pressure canner reaches the temperature needed to destroy the spores that cause botulism. This is not a preference or an old-fashioned caution. It is a matter of safety, and the rest of this entry explains why.

Safety note (read before you can anything)

Home canning done wrong can cause botulism, a rare but potentially fatal illness. To can safely, follow tested, current recipes from a trusted authority such as the USDA Complete Guide to Home Canning or the National Center for Home Food Preservation, and do not improvise processing times or methods. In brief: high-acid foods (most fruits, jams, pickles, tomatoes with added acid) can be safely processed in a boiling-water bath; low-acid foods (vegetables, meats, beans, most mixtures) must be processed in a pressure canner that reaches about 240 degrees Fahrenheit. Never use outdated shortcuts such as open-kettle canning, oven canning, or simply sealing hot food in a jar without correct processing. If a canned food's seal has failed, or the contents look, smell, or spurt out wrong, do not taste it. When in doubt, throw it out.

How canning began

The story starts with a military problem. Around the turn of the nineteenth century, France sought a better way to feed its armies, and Nicolas Appert, a chef and confectioner, spent years working on it. He found that food sealed in glass jars, closed with cork and wax, and heated in boiling water for a long time did not spoil. In 1810 he was awarded a substantial prize by the French government for the method.

What makes Appert's achievement striking is that he had no idea why it worked. The role of microorganisms in spoilage would not be understood for decades. He had discovered, purely by careful experiment, that heat plus a sealed container preserved food.

The jar that brought canning into the home came later. In 1858 John Landis Mason patented a glass jar with a threaded neck and a screw-on metal cap that pressed down on a rubber seal, creating a reliable airtight closure. The Mason jar made home canning practical, and it remained central to the practice for the next century. Early home canners still used a process much like Appert's, sealing and boiling, which was cumbersome and, by modern standards, not always safe.

What we know now that they did not

The crucial knowledge came in the twentieth century. Scientists identified the bacterium Clostridium botulinum, whose spores can survive hours of ordinary boiling and, in a sealed low-acid environment without oxygen, can produce the toxin that causes botulism. This single fact reshaped safe canning, because it explained why some historical canning was risky and why boiling alone is not always enough.

The dividing line is acidity. In high-acid foods, an acidic environment prevents those spores from producing toxin, so high-acid foods can be safely processed at boiling-water temperature. In low-acid foods, there is nothing to hold the spores in check, and they can only be destroyed by heat well above boiling. Reaching that temperature requires a pressure canner, which traps steam to raise the internal temperature to about 240 degrees Fahrenheit, far above the 212 degrees of boiling water. The households of the nineteenth century canned without knowing any of this, which is why some of their methods were unsafe even when they usually got away with them.

High-acid versus low-acid, in practice

The practical rule follows directly from the science, and it is the heart of safe canning.

High-acid foods can go in a boiling-water bath. These include most fruits, jams and jellies, pickles, and properly acidified tomatoes. A strawberry jam, for instance, is high-acid and water-bath safe, which is why it is a good first project.

Low-acid foods require a pressure canner. These include vegetables such as green beans and corn, all meats and poultry, and most mixed dishes. There is no safe way to can these in a boiling-water bath, and no tested recipe will ask you to.

Because the line between the two categories is not always obvious, the essential discipline is to follow a tested recipe from a current authority for the specific food you are canning, rather than adapting a recipe or guessing. The processing time and method in a tested recipe exist for safety reasons, not convenience.