How to Make Your Own Yogurt – Simple Science

Yogurt is one of those things that we know comes from milk, but we’re not really sure how it turns from milk to yogurt. It’s actually really simple, and we can make our own yogurt using only 2 ingredients, a thermometer, and a bit of science.

Stuff You’ll Need 

• 1 pint of whole milk
• 1-2 tbsps plain live yogurt*
• A thermometer, a sterilised storage jar, a warm place

* Most natural yogurt is live, but check for any added ingredients such as sweeteners, gelatine etc., that might alter the chemical makeup. We just used a common-or-garden supermarket-own brand.

Let’s Get Going

1. Heat up your milk until it reaches 70 degrees centigrade (160 degrees fahrenheit) on your thermometer. Stir it regularly to make sure it doesn’t burn.

2. Take it off the heat and get a grown-up to pour it into your jar. Put the thermometer into the jar. When the temperature gets to somewhere between 43-48 degrees centigrade (110-120 degrees fahrenheit) you can stir in the yogurt. This takes around one hour. Adding one spoon of yogurt will give you runny yogurt, and two spoons will give you a thick (Greek style) yogurt. 

3. Close the lid. Now you need to keep your yogurt/milk mix warm. There are several ways you can do this:

• Wrap your jar in a cloth and keep it in an airing cupboard or on top of a radiator kept at a moderate/low heat.
• Wrap it in a cloth and keep it on a heated blanket.
• Put the jar in a cool box/bag filled with warm water so it surrounds the jar. Make sure to change the water regularly to keep it warm.

4. After around 10-12 hours (or overnight) you should have yummy yogurt. You can leave it longer and it will be fine, the taste will just be a little more tangy. And that’s how you make yogurt!

So What Happens to Turn the Milk into Yogurt?

It’s all about bacteria!

The bacteria comes from the live yogurt we add, and when heated to warm conditions the bacteria causes something in milk called lactose (milk sugar) to turn into lactic acid. This is what makes the milk thicken up and turn into a tangy-tasting yogurt. This process is called fermentation–yogurt is basically fermented milk.

Bacteria loves warm conditions, this is why we have to keep our mixture warm, to help the bacteria do its job.

But I Thought Bacteria Was Bad

There are good bacteria and bad bacteria. We get rid of bad bacteria by heating our milk. The good bacteria in yogurt helps our tummies to do a good job and keeps us healthy. We already have some good bacteria in our tummies, and it helps to keep us free of bugs and illness.

Yogurt is also high in something called calcium, which helps us grow strong bones.

What To Do With Your Yogurt:

• Add fruit and honey for a healthy snack.
• Add it to your homemade granola for an ultra-healthy breakfast.
• Use it in a yummers smoothie.
• Stir through some fruit sauce or mashed up fruit and freeze it for a healthier alternative to ice cream.
• Use it to make quick soda bread.
• Leave at least 2 tablespoons at the bottom of the jar to make your next lot of yogurt. If you do this, you never need buy yogurt again!

So, now we’ve learned how to make butter, yogurt, cheese, and ice cream–all of these are made from milk. Can you think of anything else that’s made from milk that you’d like to know about? Let us know.