Why Does Milk Go Sour? Tiny Microbes Make Acid!

What Crafty Clover says in this video

Intro

Hi! I'm Crafty Clover! Let's discover something amazing. Why does milk go sour?

The Big Idea

Fresh milk is smooth and sweet. But old milk can smell sour, and turn thick and lumpy. Yuck! The reason is tiny living things called bacteria, having a milk party. Let's find out what they do!

Milk Sugar

Step one: milk has sugars that microbes can eat. Milk's natural sugar is called lactose. Say it: LAK-tohss! Milk is heated to kill most germs, but a few tough bacteria survive, and slowly multiply, gobbling up that sugar.

Make Acid

Step two: those microbes make acid. As the bacteria eat lactose, they give off a sour chemical, called lactic acid. The more bacteria grow, the more acid builds up in the milk.

Sour and Lumpy

Step three: acid makes milk taste sour, and get lumpy. Acids taste sour, like lemon juice. And the acid makes the tiny proteins floating in milk stick together into clumps. That's why sour milk gets thick and lumpy!

A Closer Look

Let's compare them side by side! Fresh milk is smooth, sweet, and full of lactose. Sour milk is full of acid, so it smells sour and has lumps. Same milk, just older, with lots more bacteria!

Quick Facts

Quick facts! Cold slows the microbes, so keep milk in the fridge! Milk left out on a warm day can turn sour much faster. Yogurt and cheese are made on purpose, with friendly bacteria and acid! Pasteurized milk is heated to kill most germs. Say it: PASS-chur-ized.

Think Like a Scientist

Now, think like a scientist! With a grown-up, check the date on a milk carton. Then give it a careful sniff. Does it smell fresh, or sour? And remember: never drink spoiled milk!

Outro

So milk goes sour because bacteria eat its sugar and make acid, which makes it sour and lumpy! Crafty Clover can be found on Amazon Books, Google Bookstore, and Apple Books. Available for purchase or download! Bye for now!