With a hammer and chisel. The can opener (1858) was patented 48 years after the tin can (1810). For most of that time, cans were way too thick to be opened any other way.
Canning food was first invented in 1810 by a French chef named Nicolas Appert. Doing so he claimed a 12,000 franc award from the French military that had been offered anyone that could come up with a solution for preserving food for the army.
Appert came up with the idea of putting food in corked glass bottles, submerging them in boiling water, and moving the food to airtight containers. Interestingly, Appert didn’t fully know how this process worked, only that air caused food to spoil faster. Canned food was patented later that year by Englishman Peter Durand, who was the first to store the food in metal containers, instead of glass.
When Durand’s metal cans were first created, there were a number of difficulties, both when manufacturing and opening the cans. The machines and factories meant to create the cans were still evolving, and it took a lot more time (and metal) to make them than they would have liked. The cans were originally made of wrought iron, and were up to 3/16″ thick. They were so tough that manufacturers’ official guidance on how to open them involved a hammer and chisel.
These iron cans were bulky enough that it took a while for canned food to catch on as a cheap, convenient food source. By the time the 1850s came around, they were starting to get lighter and thinner, using steel as the main material. As the cans got thinner, it was finally possible to puncture the lids without using heavy tools. American inventor Ezra Warner capitalized on the opportunity and invented the first ever can opener, though it was not without problems of its own.
Warner designed a pointed blade that, when pressed into the can, was prevented from penetrating too far into the contents by a guard. The guard then swung out of the way and a second curved blade (or sickle) cut around the top of the can with a saw-like action, which, unfortunately, left quite a jagged edge. Though never a big hit with the public, Warner’s can opener served the US Army during the Civil War (1861-1865) and found a home in many grocery stores, where clerks would open cans for customers to take home.
In the years following Warner’s invention, numerous innovators have turned our cans and can openers from unwieldy, bulky messes into the quick, reliable, and safe items we use regularly today.