People are only just learning what it means when Coca-Cola bottles have a yellow cap

Coca-Cola has become known for its iconic red and white labelling, but some bottles of the company's iconic drink have a subtle - but important - variation.

No, we're not talking about the different kinds of Coke, like Diet Coke or Coke Zero; this is the regular, full-fat Coke, but with a change in the packaging - a yellow cap on the bottle.

The design of Coca-Cola bottles has changed a lot since it was first sold in 1886 in Atlanta, but the instantly recognizable script with its flourishes has made it easy to spot.

Over the years, the red color has come to be associated with a rethinking of Saint Nicolas, with a Coca-Cola advertisement being the final piece in Santa's metamorphosis from the early Christian saint from what is now Turkey to the ruddy-cheeked, jolly man clad in red and white.

Some bottles have a yellow bottle top (kosherguru/Instagram)

But while the reason behind Coke's red branding is actually to help tax officials tell it apart from barrels of alcohol, which were taxed while the soft drink wasn't, there's a very different reason behind the yellow caps on some bottles.

This isn't because the company is stepping away from its iconic branding; it's actually to do with religious tradition.

Bottles of Coca-Cola with a yellow cap are actually being marked out as kosher, so they are suitable for practising Jewish people to consume.

The caps are useful during the period of Pesach, or Passover, which marks the liberation of Jewish people from slavery in Egypt.

Most Coke bottles have a red cap (Smith Collection/Gado/Getty Images)

During this period, some foods and drinks are prohibited, including beer and liquor, as well as oats, wheat, barley, rice, and, crucially for our purposes here, corn.

Corn is particularly important here because Coca-Cola is made using corn syrup, so that means that the regular variety would not be permissible.

However, the bottles with a yellow cap are a special variety of Coke that have been produced without using the corn syrup - with the cap indicating that it is kosher-approved.

Users on Twitter took to the social media platform to share their surprise that they had only just realized the meaning behind the yellow caps.

One person said: "Just learned Coca-Cola does special sodas with yellow caps to indicate they're kosher," while another said the yellow cap "means it's kosher for Pesach. I just learned about it this year myself".