Why do beer bottle caps have 21 teeth?

Review expert: Luo Huiqian, researcher at the Institute of Physics, Chinese Academy of Sciences, popular science writer

In summer, of course, it goes best with beer, crayfish and barbecue.

Whether in a bustling night market or food stall, or a pub or nightclub full of petty bourgeoisie, or a KTV or bar, beer is a well-deserved must-order drink. Inviting a few friends to eat skewers and drink beer on a summer night is simply a great blessing in life.

Source: pixabay

However, except for a few beer enthusiasts, most people have to ask the store for a bottle opener every time they go out to drink. Otherwise, it is either difficult to open the bottle or dangerous to use other tools. Faced with a circle of small serrations on the bottle cap, it seems that an ordinary bottle opener is really the best?

So why are beer bottle caps so peculiar yet uniform? Let me tell you a secret: if you look carefully, you will find that all beer bottle caps have 21 teeth! Why is that?

1. The beer bottle cap needs to ensure sealing

When people drink beer, they will feel bloated when they drink too much. This is caused by the large amount of carbon dioxide in the beer. Carbon dioxide is a very important additive in industrial beer. Its presence can reduce the oxygen content and inhibit the oxidation of beer. In addition, the anaerobic environment can inhibit the growth of harmful bacteria and enhance the antiseptic ability of the beer.

At the same time, the presence of carbon dioxide will also create a unique "killing" taste, which is also one of the flavors of beer. However, to ensure that a large amount of carbon dioxide is safely stored in the beer, a highly sealed bottle cap is required.

Taking my country as an example, the current national standard beer bottle cap is GB/T 13521-2016 crown bottle cap.

Beer bottle cap structure

Source: GB/T 13521-2016 Crown Cap

The bottle cap has 21 serrations, a metal base, and a sealing gasket.

The functions of each part are as follows: the metal base is mostly made of tinplate , which is used to ensure the stability of the bottle cap and ensure the safety of beer transportation, so that the bottle will not burst in high temperature or bump environments. The sealing gasket ensures that the gas and liquid in the bottle will not leak, and also increases the friction between the beer bottle cap and the bottle mouth to prevent the bottle cap from sliding.

The sealing gasket of the bottle cap is also particular. Studies have shown that the double-groove structure of the bottle cap gasket with PVC granules has better sealing performance. Today's protagonist - the most critical serration - is an important parameter to ensure the firmness of the bottle cap . Nowadays, the serration of the bottle cap has basically been fixed at 21.

Beer bottle caps

Source: tipsmake.com

2 History of changes in the number of sawtooth

The 21 teeth on the beer bottle cap may seem ordinary, but they are actually the optimal result obtained by manufacturers after continuous attempts.

At the end of the 19th century, all bottle caps were screw caps. Because the screw caps were not tight and often caused the soda water to spoil , an American mechanical engineer William Painter tried to press the bottle cap down everywhere, which was the original crown cap. Because it looks like a crown, this bottle cap is also called "Crown Cork".

William Pate's crown cap

Source丨PAINTER, WILLIAM,THE CROWN CORK AND SEAL COMPANY. BOTTLE CLOSURE:CAD63427[P]. 1899-07-10.

Pater applied for a patent for this, and the beer bottle cap was also produced by a machine called "Painter", but the number of teeth on the bottle cap at the beginning was different from the popular ones today, it had 24 teeth.

In the 1930s, when manual capping gradually changed to industrial automated capping, the disadvantages of the 24-tooth design became apparent - the 24-tooth design was very easy to clog the hose used for capping.

To solve this problem, the number of teeth was changed to 23 so that an odd number of teeth would no longer get stuck in the hose.

Drawing of a machine for making beer bottle caps

Source丨CROWN CORK AND SEAL COMPANY. MACHINE FOR MAKING CLOSURES FOR BOTTLES AND THE LIKE.:US19070395758[P]. 1908-05-19.

However, the final number of teeth was fixed at 21, mainly for two considerations: sealing and safety of opening the lid .

When the bottle cap still has 23 teeth, the large number of teeth makes it too tight and difficult to open with a bottle opener. At the same time, the air pressure in a bottle full of beer is about 0.3 megapascals (0.3 MPa, which is about 3 atmospheres), and a bottle cap that is too tight is not safe when opening.

Various beer bottle caps

Source: pexels

To further improve it, scientists have discovered that beer bottle caps are more secure when the number of teeth on them is a multiple of 3, and that bottle caps with 21 teeth are easier to open, greatly reducing the risk of bottle explosions.

Moreover, the design of 21 serrations combines high bite and sufficient safety when opening the cap. The 21 folds can make the contact area of ​​each fold on the bottle cap as large as possible, increase the friction between the bottle caps, and ensure firmness.

At the same time, this is also the most suitable number of folds for opening a wine bottle. If there are more folds, the bite force will be too large, and the bottle opener will be difficult to open. Excessive force may cause damage to the bottle body and insufficient safety; if there are fewer folds, the sealing will be insufficient. Therefore, the 21-tooth bottle cap has been used until now.

3What is the difference between canned beer and bottled beer?

Most beer sold on the market is canned or bottled . Although the brand series is the same, the taste of beer in two different containers is different. When packaging beer, carbon dioxide needs to be filled. Since cans are more easily deformed than glass bottles, the content of carbon dioxide filled in canned beer needs to be lower than that in bottled beer . Therefore, canned beer does not taste as "refreshing" as bottled beer.

Not only that, canned beer has a higher oxygen content and its degree of oxidation is also higher than that of bottled beer. If both are left for a long time, under the action of oxygen, canned beer is more likely to change its taste due to oxidation.

However, there is still a demand for canned beer, which is easier to carry and store than bottled beer. Beer needs to be stored away from light. If beer is stored in the light for a long time, the substances in the beer will undergo chemical reactions to produce a smelly substance, and the beer will have deteriorated. Although the glass of bottled beer is dark, its light transmittance is still weaker than that of cans. Bottled beer is more likely to deteriorate after being exposed to light for a long time.

Canned vs Bottled Beer

Source: Internet

In short, if you cannot create good light-proof conditions or need to carry it, canned beer has more advantages than bottled beer.

It is true that the existence of beer has greatly enriched people's social and dining life. People can have a drink with friends in their spare time or drink with relatives and friends at the dinner table. Everyone can drink happily in a state of tipsiness. However, a survey by the international authoritative medical monograph "The Lancet" shows that every drop of alcohol is harmful to the human body, so I hope everyone will drink as little as possible, and it would be even better if they can not drink at all.