How many aliases (pointed parts) are there on a beer bottle cap, and why?

You’ve seen the jagged caps used on beer bottles. Every bottle in the world apparently has the same number of pointed parts called aliases.

Count them and you’ll see that there are…

21!

Why is that? Well, after years of research, dynamics experts found that bottle openers can grab the cap with a stable force if the number of areas that come into contact with the opener is a multiple of three. They found that if there are 24 aliases, the force applied is too strong to remove the cap easily, while if there are 18, the seal is too weak and lets out the carbonic acid that makes beer fizzy. So 21 it was!
Fascinating!

By the way, these caps are called “crown caps” in both English and Japanese. They were invented by William Painter in the USA in 1892, and got their name because if you turn them upside down they look just like a crown.

And since the same caps are used around the world, you can share this bit of bar trivia wherever you go!