The disc under the bottle cap is meant to help with carbonation
On a hot summer afternoon, there are few things that are more refreshing than a cold can of Coke. However, there is a slim chance you have never wondered why a soda bottle’s cap has a little plastic disc underneath it. It may appear superfluous, yet it is there for a very specific reason.
Although you are probably not interested in the science behind it, the deal here is that the disc under the bottle cap aids in the trapping of carbon dioxide within the bottle. You will not be able to enjoy the fizz in your drink without it. So, yes, you own a lot to this little piece of plastic under the cap.