Why Does Hot Cocoa Form a Skin on Top?

What Crafty Clover says in this video

Intro

Hi there, curious minds! I'm Crafty Clover! Let's discover something amazing. Why does hot cocoa form a skin on top?

The Big Idea

Hot cocoa forms a skin on top because proteins and fats link together as water dries away! The top of the cup loses water into the air, so the milk proteins bunch up and join. That thin film is a tasty science lid.

Water Escapes

Step one: water escapes. Hot cocoa gives off steam, which is water turning into gas at the top of the cup. That leaves the surface layer drier and thicker.

Proteins Link

Step two: proteins link up. Milk has proteins, and heat and drying make them unfold and stick to each other. They form a stretchy net on top, and fats get caught in it.

A Skin Forms

Step three: a skin appears. The net grows into a thin skin that wrinkles when you touch it. If you remove it, a new one can form as the cocoa keeps cooling and drying.

A Closer Look

Let's take a closer look! Cocoa sits in a cup, still and cooling. Water slowly leaves the top as steam. Milk proteins and fats bunch together. And they make a thin, wrinkly skin.

Quick Facts

Quick facts! The same thing makes a skin on warm pudding and custard. Stirring breaks the skin up, and a lid keeps it from forming. Cocoa powder is ground cocoa beans, and it adds flavor and color. Hot cocoa can burn, so wait until it is only warm.

Think Like a Scientist

Now, think like a scientist! Ask a grown-up to pour a mug of cocoa. Wait until it is only warm, not hot. Look at the skin on top. Never taste hot cocoa.

Outro

Cocoa skin is a thin film of proteins and fats. Science is amazing! Crafty Clover can be found on Amazon Books, Google Bookstore, and Apple Books. Available for purchase or download! Bye for now!