Microbes are all around us — in the dirt, on our food, in the air, on our skin. We often think of them being bad or pathogenic — for example, flu viruses, strep bacteria, or ringworm fungus. But those “bad bugs” are just a small part of human interactions with the microbial world. In the biotechnology laboratory, we have figured out ways to harness the power of microbes to produce products that make human life easier. In modern times, humans have been able to genetically alter microbes to make molecules like insulin, vitamins, biofuels, and biologic medications. However, humans have been using microbes for years to preserve foods and make them more stable. You may have heard of this as fermentation. Many of our favorite foods like sourdough bread, yogurt, kimchi, pickles, and kombucha are produced by fermentation. Believe it or not, it is an easy experiment to perform in your kitchen laboratory!
Making sourdough is pretty easy. There are lots of ways to make a starter and to bake the bread (and you may have tried a few already on your own! We love the guide created by King Arthur Flour, which goes into some of the history and science of the bread. Plus, they have a lot of advice and suggestions on creating a starter, and even the “best” sourdough recipe. You may want to try a bunch of different recipes though, to see which one you like best. And then you get all that delicious bread. You know… for science!
Once you get your starter set up, you can try different experiments with your starter discard to see how the doubling time is affected. For example, does the temperature of the room affect the doubling time? The humidity? Light vs dark? There are so many questions to ask, and so many things to test. Like a good scientist, be sure to write down your hypothesis, variables, protocol, observations, and data. (Don’t forget to download our Summer Camp Activity Guide, which contains a lab report page!)
There are also a lot of great websites with lesson plans to help guide your exploration. Here are a few we liked.
- https://zerowastechef.com/2015/10/08/kitchen-science-for-kids-sourdough-starter-lesson-plan/
- https://blog.scistarter.org/2022/03/sourdough-for-science-how-you-can-create-a-tiny-world-in-a-jar/
- https://robdunnlab.com/projects/wildsourdough/
Do you want to take your microbiology analysis one step further? Using a microscope and the Edvotek Gram Staining Kit, you can smear some of your culture on a slide and look to see what happy bugs are contributing to the fermentation in your starter. We haven’t tested this experiment, but we did see this beautiful stain on Reddit (right). To do this, I would recommend taking a very small pin point of your culture and diluting it in sterile water before smearing it on the slide. You may need to play a little bit with the quantity of starter to water so that you can see a lot of microbes, and not a ton of gooey gluten. Some microbes you may see in your starter include:
- Yeasts — these are fungi, which are eukaryotic cells. They can be the common bread/brewers yeast, Saccharomyces cerevisiae, or wild strains of yeast that might be more common in your region. In fermented foods, yeast breaks down sugar in to ethanol and other molecules that contribute to the aroma of fermented foods. They also produce carbon dioxide as part of its metabolic waste, helping to leaven the bread.
- Lactobacillis — This is a genus of gram positive, rod shaped bacteria that are very commonly found in fermented foods. You may have heard about these bacteria already because they are common in foods like yogurt or kefir. They are also found in our intestines as part of the healthy flora and fauna necessary for digesting food. They break down sugars into lactic acid, producing some of the sour/funky flavors of fermented foods.
- Acetic acid bacteria — these are gram negative, rod shaped bacteria that are often used in food and chemical applications because they break down sugars and produce acetic acid — which we also know as vinegar! The acetic acid present in the sourdough starter and fermented foods also contributes to the tangy quality. The acetic acid also serves as a natural preservative in foods, bringing the pH down to a level that prevents spoilage from other microbes.
If you don’t have a microscope at home, you can also build yeast and bacteria using our Origami Organelles. These are models your budding scientists can color and build at home to examine the parts of the microbes that are essential for the growth of the sourdough starter.
If you make sourdough or try any of these experiments, please let us know! Be sure to tag us on social media, or you can contact us at curriculum@edvotek.com. You can even be featured here on our blog! We love to see student science in action.
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