Canning

The idea of sealing food in a tight container goes back to 1809. Napoleon, the French Emperor was fighting wars all over Europe, and his army needed huge supplies of preserved food. He offered a prize of 12,000 francs (about Rs. 14 lakh in India today) to anyone who could find a method. The prize was won by Nicolas Appert, A French brewer.

He discovered that if you sealed food airtight immediately after cooking it, it would remain fresh as ever. That's because bacteria and fungi cannot enter from the air, and all the ones in the cooked food would have died.

In the early days, food was put into a steel canister, and then a steel plate would be welded on top of it. Over time, the word 'canister' got shortened to 'can'. While steel cans are easy to transport, the food reacts with the steel producing rust and other toxic stuff.

Tinning

The trick is to make the can out of steel and tin. A very thin sheet of tin is hammered onto a sheet of steel. This way, you make a material called tinplate steel. You can then roll this sheet into a cylinder, such that the tin comes on the inside. Then you cut a circle from the sheet and weld it to the can, with the tin facing inside. Now pour the food in, and seal off with another plate.

The steel on the outside helps keep the can firm. It won't get any dents while the can is being transported. The tin on the inside prevents food reacting with the steel. Over time, the name tinplate can got shorted to tin!

Nowadays, a whole lot of cans are actually made of aluminium, because it's cheap and can be recycled. Here's a video on how cans are made:

(Video sourced from YouTube.)

Malleability

Try this experiment in school. Take a few sheets of different metals, like steel, tin and aluminium. It's best if they have the same thickness. Try to roll them into shapes. Which rolls easily? Malleability is the name scientists give to how easily you can roll or hammer metals into different shapes.

If there's a workshop near your school, you can ask them to help you weld a tin can into shape. Ask them to make sure that there are no sharp edges. While it may not be good for food, you can keep flowers or pencils in your own handmade tin can!