Back in 2019, a delicious drink craze using two everyday ingredients everybody already had in their cupboards went worldwide. People started taking milk and adding it to Coca-Cola. 

The concept has actually been around for quite a long time, not just amongst beverage perverts. Milk and Pepsi was famously drunk by Laverne on Laverne and Shirley, South Africans call the mix "brown cow" (mmm, appetizing name, South Africa!), in India it's known as "Doodh soda", and in Birmingham, UK, where it's basically now the official city drink, it's simply called "milk coke".

But the mix has only recently surfaced in the mainstream after it went viral last year, resulting in a lot of confused and disgusted news anchors being forced to try it live on air.

Apparently, until then, everybody has only been drinking it home alone in shame, whilst trying not to think about diabetes.

Though it sounds like an abomination, it's actually pretty tasty if you get the ratios just right (two-thirds coke to one-third UHT milk, according to a recipe passed down through the generations of Brummies to myself).

However, if you get them wrong – or leave the drink to settle for too long – it can all get pretty disgusting, as this viral experiment has shown. Brummies, you might want to put down your beverage before you watch, it is not pretty.

So, why does adding milk to Coke turn the liquid clear?

As you probably know, Coke is slightly acidic, containing phosphoric acid. When acids come into contact with milk, the milk curdles. So when the Coke gets mixed with milk, the phosphoric acid begins to curdle the milk into little clumps, which sink to the bottom as the phosphate molecules bond to the calcium molecules in the milk, The Higher Learning reports, as is outlined in this delicious equation:

3Ca + 2H₃PO₄ —> Ca₃(PO4)₂ + 3H₂

Whatever's left of the milk coke floats to the top, being lighter than the tricalcium phosphate which has sunk to the bottom, taking most of the color with it. If you make your milk coke in a bottle, beware that the hydrogen left over from the phosphoric acid molecules is released as gas (H₂), floating to the top of your bottle.

So stay safe, milk coke fans wherever you may be. Make sure you drink it before it has the chance to curdle, or be prepared to chew.