Why do beer bottle caps have exactly 21 teeth?

Twenty-one is the point where the crimp grips evenly all the way round without the metal tearing. William Painter settled on it in the 1890s after testing other counts, and the number stuck because it works — most crown caps you open today still have exactly 21.

Why doesn't beer use screw caps like wine?

Some does. But a crimped crown cap holds carbonation pressure better over long storage, costs a fraction of a cent, and its seal does not loosen if the bottle is knocked. For a carbonated drink shipped in crates, it is still the better engineering answer.

Are crown caps recyclable?

Yes — they are steel, and steel is one of the most recycled materials there is. The catch is that loose caps are too small for most sorting machinery. Collect them in a steel can and crimp it shut, and the whole thing gets sorted correctly.

What is the liner inside a bottle cap made of?

Originally cork. Since the 1960s it has been a thin food-safe polymer disc, which seals better and does not impart flavour. The visible metal is only half the seal — the liner is what actually keeps the carbonation in.

August 29, 2026 · 2 min read

Why Beer Still Uses Crown Caps (and Why That's a Good Thing)

The crown cap was invented in 1892 and has barely changed since. Here's why 21 teeth, a cork liner and a stubborn seal beat every replacement anyone has tried.

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The crown cap is one of the most successful pieces of design in the history of packaging, and almost nobody thinks about it. Here is the short version of why it is still on your bottle.

A Baltimore inventor and a problem with beer

In 1892, William Painter patented a small crimped steel disc with a cork liner and a fluted skirt. Before it, bottled beer was sealed with wire-and-porcelain swing tops, corks, or various contraptions that leaked, cost money, and needed cleaning between uses.

Painter's cap was different in one crucial respect: it was designed to be thrown away. Single-use was the innovation. It made the seal cheap enough that mass-market bottled beer became viable at all.

He also had a second good idea — he invented the bottle opener, and sold that too.

The 21 teeth

The fluted skirt is not decorative. Each flute is a crimp point, and 21 is the count at which the metal deforms evenly around the entire circumference without tearing.

Fewer flutes and the seal gaps between crimp points. More and the metal work-hardens and splits. Painter tested his way to 21 and the industry has had no reason to move since. Pick up any beer cap and count them.

Why nothing has replaced it

Screw caps exist and work fine for wine. For carbonated beer they lose on three counts:

Pressure. A crimped cap holds several atmospheres indefinitely. A threaded closure relies on constant gasket compression, which relaxes over months.
Knock resistance. Crates of bottles get thrown around. A crown cap does not loosen; a screw cap can.
Cost. Fractions of a cent, at billions of units a year.

Ring-pulls, corks and swing tops all come back periodically for premium bottles. They come back as statements, not as replacements.

The liner does the actual sealing

The metal is the clamp. The seal is the thin disc inside — cork until the 1960s, now a food-safe polymer that seals tighter and adds no flavour of its own.

This is why a cap that looks fine can still have let a beer go flat: the liner failed, not the crimp.

What this means when you open one

A crown cap is engineered to grip and to resist being levered off. That resistance is the point, and it is exactly why the moment it gives way is satisfying.

It is also why we built an opener around the release rather than around the removal. The Beer Mortar does not pry the cap off sideways — it converts one palm strike into a vertical launch, and 130 years of stubborn steel engineering gets to make an exit.