The Biology of Yogurt

We’re growing bacteria in our house.  And not just the preschool snotty nose kind.  It’s yogurt, the yummy, healthy kind of bacteria.  And it makes for a tasty learning experience for kids. Make a homemade batch of yogurt to help kids understand how it all works.  This post contains affiliate links.

Learn all about the biology of yogurt and why it's good for us by making a homemade batch of it. It's tasty snack time STEM learning for kids!

Learning with Homemade Yogurt

We eat a lot of yogurt in our house.  It’s a go to food for my picky eater daughter and Greek yogurt works for my protein-loving husband and me.  I was kind of shocked by our yogurt grocery bill so I bought a yogurt maker {affiliate} a few months ago. $21 totally well spent because the yogurt I make is the best I’ve ever tasted. Plus there’s definitely something rewarding about making your own food staples, especially when it’s so easy.

Sampling Yogurt Left Brain Craft Brain

The Biology of Yogurt

So what exactly is happening inside that yogurt maker?  My daughter decided that she wanted to photo-bomb all the pics of us making yogurt, so I hope you enjoy the silly shots!  :)

Yogurt Maker Closeup Left Brain Craft Brain3

Yogurt gets it’s characteristic tart flavor from the fermentation of milk by bacteria, typically Lactobacillus bulgaricus and Streptococcus thermophillus.  As the bacteria consumes the sugar (lactose) in the milk, they produce lactic acid. The lactic acid lowers the pH of the yogurt, making it tart and also causing the milk proteins to bind and thicken. The fermentation process has two other benefits.  The partial breakdown of the lactose in the milk makes it easier to digest and the lower pH keeps bad bacteria from spoiling the yogurt.

Yogurt Jars Left Brain Craft Bran

A good way to experience the fermentation in action is to sample the yogurt a few times throughout the incubation process in the yogurt maker.  The longer the yogurt cooks, the tarter it gets because more lactose has been converted to lactic acid.  This sampling may cause you to lose a few jars along the way, but all in the name of learning, right? It’s rare that you can actually taste bacteria in action. Let me rephrase that… It’s rare that you actually want to taste bacteria in action!

You can find the yogurt recipe I used at the bottom of the post and for more on fermentation, check out my Biology of Bread post.

Other Ways to Visualize Bacteria in Action

It can be hard for kids to understand things that they can’t see like the bacteria in yogurt.  So I added a few other things to the afternoon play to help The Babe understand.

“Yogurt” Sensory Bin

I pulled together a quick and easy “yogurt” sensory bin for her to play with.  We played yogurt shop all afternoon with this!  A bin full of water colored with white food coloring {affiliate} became the yogurt.  Have you tried white food coloring yet?  It’s new to me and it’s awesome.  Just a couple of squirts made the water look just like milk.  And water beads {affiliate} were the bacteria.  Get the multi-colored ones to show that there’s more than one kind of bacteria working in yogurt.  Add some spoons and bowls and you are set.

Yogurt Sensory Bin Closeup Left Brain Craft Brain

Kombucha Tea

Have you ever tried Kombucha Tea?  It’s a fermented drink made from tea, sugar, bacteria and yeast.  You can find it at places like natural grocery stores and Whole Foods.  The cool thing (and some people would say the yucky thing) is that you can actually see the colony of bacteria and yeast in the bottom of a bottle.  Some people claim that ingesting the colony stimulates the immune system and improves digestion.  The jury’s still out on it’s benefits, so you could just look at it instead of drinking it if it skeeves you :)  And please don’t give this to anyone with immune system issues or very small children.

Kombucha Left Brain Craft Brain 2

Homemade Yogurt Recipe

  • 4 cups milk (any fat % works)
  • 3/4 cup yogurt (store bought or previously made)
  1. Pour milk into a high sided sauce pan with lots of room.  Heat milk over medium heat, stirring frequently, until boiling.  You also want to see bubbles start crawling up the sides of the pan.  Remove from heat and let cool until it reaches 95º.
  2. Once milk has cooled, strain it through a fine strainer into a large mixing bowl.
  3. In a separate bowl, mix 3/4 cup yogurt with 1 cup of cooled milk.  Whisk until smooth and add back to the cooled milk.  Mix until incorporated well.
  4. Evenly distribute milk / yogurt mixture across all jars and place them in the yogurt maker.  Do not put the caps on them (I always forget this!) and place the lid on the maker.  Let incubate until the yogurt reaches the desired tartness and thickness.  8 hours for whole milk, 9 hours for 2% and 10 hours for skim is a good place to start but you might need a few batches to get your ideal timing set.
  5. Put lids on yogurt jars and refrigerate.  Yogurt should be good for two weeks if refrigerated properly.  Be sure to save some as a starter for your next homemade batch, too!

Don’t have a yogurt maker? First, think about buying this yogurt maker {affiliate} for sure (I love it!) or make Granny Miller’s Slow Cooker Yogurt.

Giving Kids the Power to Create

STEAM Power Yellow

This post is the last week in month long series with some of my favorite bloggers who all love STEAM. Because learning with Science, Technology, Engineering, Art & Math gives kids the power to do almost anything they can dream up. Like make a train move or colors change.  This week is all about ways to Grow.

DIY Salt Crystal Landscape  //  Babble Dabble Do

All About Tinker Trays  //  Meri Cherry

14 Activities with Balloons  //  All For the Boys

Transforming Ninja Star  //  What Do We Do All Day?

How to Grow Aragonite Crystals  //  TinkerLab

Building with Jelly Beans  //  Lemon Lime Adventures

Did you see last week’s If-Then Backyard Coding Game for Kids?  Teach kids one of the building blocks of programming without a computer in site.  Or do some Spring Play or make a Color Changing Chemistry Clock.  Or the week before where we all learned to Fly.

Love Kitchen Science? You'll love STEAM Kids in the Kitchen!

Looking for some more STEAM inspiration that use can use right now? Instant gratification style? Check out STEAM Kids in the Kitchen: Hands-on Science, Technology, Engineering, Art, & Math Hands-On Recipes and Activities for Kids ebook! It’s packed full of 70+ Bring STEAM learning fun into the kitchen with these hands-on activities and recipes. Learn what makes bread rise, colors change, and how to make an epic pudding model of the Earth.


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14 thoughts on “The Biology of Yogurt”

  1. I’ve always wanted to try making my own yogurt! I love how you explored the science behind the process!

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