Kitchen Science for Kids: Sourdough Starter Lesson Plan

If kids are more in touch with the natural world, they will feel less inclined to destroy it as adults. While I do believe kids need to play outside in nature, they can also learn about entire ecosystems right in their kitchens, using only a handful of basic ingredients.

Any of the fermented recipes I have posted on my blog can serve as a good science lesson but I decided to start with sourdough, the homiest of foods and one that almost all kids will eat. This lesson covers only sourdough starter. If you and your student want to later bake bread, you can find the recipe here.

Bubbling sourdough starter ready for baking
Bubbling sourdough starter ready for baking

What your kids will learn 

  • History
  • Biology
  • Math
  • Vocabulary
  • Responsibility
  • Time management
  • Following directions

Vocabulary

Bacterium (plural bacteria): Microscopic, single-celled organisms that live in soil and water and on plants, animals and other matter. Their purpose in life is to reproduce.

Ecosystem: All the living things in a given area. All things that live in an ecosystem are dependent on one another.

Microbes: A tiny living thing that can be seen only through a microscope, such as bacteria and yeast.

Symbiosis: A mutually beneficial and dependent relationship between two groups.

Yeast: Another class of microscopic, single-celled organisms which, like bacteria, live everywhere. Yeast makes bread rise.

Lesson Plan

Time requirement

The starter should be ready for baking within a couple of weeks, with very little active work done to it.

Equipment

  • Kitchen scale (optional)
  • Thermometer (optional)
  • Two glass measuring cups or small glass or ceramic bowls
  • Measuring spoons
  • Fork
  • Small breathable cotton or linen cloth
  • Flour
  • Water

What is a sourdough starter?

A sourdough starter, also known as a sourdough culture, contains living bacteria and yeast that transform flour and water into a leavening agent. Filled with gas bubbles, a leavening agent makes bread dough rise during baking. A sourdough starter also adds flavor and aroma to bread. It most commonly consists of only flour and water. This living thing needs regular feeding to keep it alive. When well cared for, sourdough starters can live for hundreds of years. The starter King Arthur Flour carries dates to the late 1700s, making it about the same age as The United States.

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Carbon dioxide creates these air pockets in a sourdough loaf

History

About 6,000 years ago in Egypt, someone baked the first loaf of bread. They likely noticed a neglected mixture of flour and water had sprung to life, bubbling away in a corner somewhere. That accidental starter would have made the first loaf rise. For thousands of years, all bread was made with a sourdough starter.

In 1857, Louis Pasteur first identified yeast under his microscope. Soon after his discovery, around 1880, industry developed commercial yeast, which contains only one strain of bacterium, Saccharomyes cerevisiae. Commercial yeast produces consistent loaves of bread quickly, which meant bakeries could bake more loaves, more quickly, with fewer workers, resulting in higher profits.

However, bread made the old-fashioned way has never completely disappeared. People bake sourdough bread all over the world. San Francisco’s sourdough bread is so famous that scientists named the main bacterium found in sourdough Lactobacillus sanfrancisensis. They later discovered that this bacterium lives in sourdough bread cultures around the world, but no one has ever found this bacterium anywhere else on the planet except for in a sourdough culture.

Related history: how a 19th century grist mill grinds flour

Method

1. In a glass or ceramic container, mix 100 grams warm water (about 110 degrees) with 100 grams flour. Your mixture will resemble thick pancake batter. Cover your container securely with your breathable cloth. Leave your container out on the kitchen counter.

2. Stir your starter several times a day. Depending on your kitchen environment, the starter should start to bubble within 3 to 7 days. At this point, begin to feed it daily.

3. To feed your starter, in a separate container, mix together another 100 grams warm water with 100 grams flour. Stir in 2 to 3 tablespoons of the bubbling starter. This is your new starter. The previous one is discard. TIP: Store your discard in the refrigerator until ready to use for making pancakes, waffles, crackers or tortillas.

4. Continue to feed the starter daily. Around day 5 or so, it should begin to double in size after feeding and fall back to its original size. This process will take several hours. It will also smell yeasty, slightly fruity and slightly acidic. When you notice these characteristics, the starter is ready to leaven bread dough.

5. Once your starter is ready for use, you can either leave it out on the counter and feed it daily, or store it in the refrigerator and take it out once a week to feed it.

You may also want to check out my stick figure sourdough starter instructions here.

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Sourdough crackers made with discarded starter

The science behind sourdough

  • Yeast and bacteria are present in the air, in the flour and on your hands. You may want to use your clean hands to mix the ingredients to inject them with more microbes.
  • As the microbes begin to reproduce in the starter, the bread-friendly ones take over and crowd out any unfriendly ones.
  • Lactobacilli bacteria convert sugars in the flour to lactic acid and acetic acid. These acids give sourdough its distinctive sour flavor.
  • Acid-tolerant yeasts thrive in the starter also. They convert sugar into carbon dioxide and ethanol. The carbon dioxide creates bubbles that make the bread rise.
  • Each microbe eats different sugars and so they do not compete with each another for food.
  • The principal yeast in the starter is Candida milleri. This acid-tolerant yeast doesn’t consume maltose, a sugar in flour starch. Without maltose, Lactobacillus sanfranciscensis, the bacteria found only in sourdough cultures, die off! Of course, microbes do die eventually, but not before they produce their replacements. When yeasts die, they break down into compounds that the lactobacilli eat. This mutually beneficial relationship between two organisms is called symbiosis. (If only all relationships went this well…)

Sources:

16 Comment

  1. Christopher Kay says: Reply

    Hi there, Brilliant post, I love it and my nephews will do too 🙂 Kind regards, Chris

    Date: Thu, 8 Oct 2015 11:15:08 +0000 To: cmkay@hotmail.com

    1. Thank you so much, Chris! That makes me so happy you’re nephews will try it 🙂 Please let me know how it goes!

  2. This is a wonderful post. May I use it in the Green Friends newsletter like I did one of yours earlier in the year? We have a section on Teaching the Children and this would be perfect for that!

    1. Absolutely Karuna! Thank you 🙂

  3. Thanks so much and can’t wait to try this with the kids.

    1. You’re welcome Christine. I think the kids will really enjoy it! Thanks for checking it out!

  4. Such a great way to get kids in the kitchen and make learning both fun & tasty! Wish my science teachers had a “sourdough bread” lesson when I was in school 🙂

    1. Thank you, Karen 🙂 Kids are natural cooks and scientists.

  5. I remember wondering when I was a child, what is yeast? Where does it come from? (we never did sourdough, just the dried stuff) Yeast is kind of magical and I can see it being a completely entrancing subject for children. I always love the idea of including children in the kitchen, and this is another great way to keep their interest. Thank you!

    1. Thanks so much! I think kids are natural chefs and scientists, so I hope this will be a lot of fun. I love the idea of including kids in the kitchen too. It’s so important!

  6. I loved this post so much and will be using it with my daughter soon!

    1. Great! I wish I had started all of this when my kids were younger. I hope you both enjoy it 🙂

  7. Hey! Hoping to attempt my first sourdough loaf soon! Couple of questions: to feed the new starter daily, do you simply add 100g water and 100g flour to it each time? And am I right in understanding you don’t start a fresh batch overtime you feed it like you do the first time? Thanks so much! 🙂

    1. Awesome! So, you don’t add 100 grams each flour and water to the existing starter. You only use a little bit of the existing starter–two to three tablespoons. So first you mix together the flour and water in a new container, then you add a bit of the existing starter to this new one. Once you’ve done it once or twice, you’ll have it down. Here is another post I wrote about making a starter. You do this only once, then you just “feed” it to maintain it: http://zerowastechef.com/2015/03/01/how-to-make-a-sourdough-starter-in-stick-drawings/

      I hope that helps 🙂

  8. Hey! Late to the party, but question on the starter! So I get the initial starter, then the second one where you only add the three tablespoons, and then you “discard” the old one. I guess my question is this: you have now “discarded” the original starter, you are on your second starter that you fed with the original, so now you make a third? And then feed that one with three tablespoons from the second batch? So essentially you will have discard every few days until your starter gets to the right stage? Mainly looking for the definition of “feed” in this instance!!! Hope this is not a silly question! Make my first sourdough!!

    1. That’s not at all a silly question, Justine. You’ll have a new starter every time. I have a dish in the refrigerator I add all the previous starters to. I use that to bake crackers and whatnot. I was also confused at first and wondered how I’d ever figure all of this out but after you’ve done it a bunch of times, you’ll have it down and you’ll get a feel for it. Once it starts bubbling, I would feed it every day. It will be more vigorous and bubbly that way. Good luck with your sourdough! It’s so satisfying to make. I wish I could bake all day 🙂

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