Wednesday, June 14, 2017

Homeschool Science: Yeast is Alive

The other day, Syd and I were baking bread together. She was making peasant bread for that night's dinner, and I had found that inexplicably, I have flaxseed in my pantry (where do I get these things?!?), and so I was making up the dough for a whole wheat and flaxseed bread recipe that I'd found on Pinterest.

I was pretty excited, because the dough also calls for steel-cut oats, which are all I have. Recipes NEVER call for the kind of oats that I have!

Although we've made that peasant bread recipe several times, it occurred to Syd on this day to ask why it has sugar in it, if the bread isn't sweet.

"The yeast eats it," I said, attention about one-quarter on her and three-quarters on my recipe. It calls for so many odd ingredients that I own but rarely use!

As soon as I finished speaking, the entire world seemed to pause, and then Syd belted out, "You mean yeast is ALIVE?!?"

It turned out to be the perfect afternoon for an impromptu homeschool science lesson!

Yes, yeast is alive. It's a lovely little fungi--in fact, it's this lovely little fungi.

I don't always encourage Wikipedia as a reference, but it's a great resource when studying living organisms, because there each entry has the entire order of classification; we like to click down the order, seeing how the categories narrow and how each species fits more specifically as they do, until finally you're left with just that one specific species of baker's yeast.

Brainpop also has an excellent video about fungi, with a lot of mentions of yeast. Syd really enjoyed it, and then came and told me all about athlete's foot while I was trying to eat lunch.

Years ago, Syd and I explored anaerobic respiration with yeast, so we repeated that same demonstration of putting a yeast and sugar solution into a bottle, then fitting a balloon over the lip of the bottle:



First there's not much to see, but after a few minutes there's already a change--


--and after an hour there's a BIG difference! That anaerobic respiration consumes sugar and expels carbon dioxide. It looks like this:



We made a second solution of yeast, sugar, and water, and as soon as that one was nice and frothy, we got out our microscopes to take a few peeks.

I LOVE our digital microscope, and we use it tons, but it wasn't suitable for viewing actual yeast cells. What we COULD see with it, however, was pretty cool--we could see the bubbles of carbon dioxide forming!



The halo of lights that you see in each bubble is not miraculous new life, but the reflection of the lights on the microscope. Syd was less wowed after I explained that to her.

Our Brock magiscope just got us to the 400x threshold for viewing the actual yeast cells. If Will continues to homeschool through high school, I am going to have to shell out for a more sophisticated microscope, but I will not be surprised if the Brock magiscope can see us completely through the middle school years.

Syd's not always terribly interested in the microscope, so this was one of her first times preparing her own slide. She kept wanting to mistake those same bubbles for the yeast cells, but I kept encouraging her to look past them, to look for the tiny dots in the background.

She found them!



I love watching a kid's absorbed face as she learns something new.

Even though the fact that yeast is a living organism was what blew Syd's mind, she's a baker at heart, and so of course we also had to explore yeast's role in baking. I saved this experiment to try another time, but instead the kids and I watched the Good Eats episode, "Dr. Strangeloaf," and then Syd and I finished our various bread loaves while Will...

Well, Will made lemon bars. There's no yeast in lemon bars, but they ARE delicious!

P.S. Check out my Craft Knife Facebook page! I share most of my homeschooling and crafty resources there.

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