The Duchess Bakes a Cake is the story of a medieval duchess who gets bored one day and decides to make a cake. She adds some yeast, and then adds some more yeast, and then more for good measure. The results are about what you would expect for a children's storybook, which is to say it completely ignores the fact that all the yeast in the world can only make a finite amount of dough stretch so far and the resulting cake carried the duchess far above the castle.
With a story like that, you obviously would have to spend time talking about baking and the role of leaveners. We started with yeast. I showed K a couple Good Eats episodes featuring yeast, because if there's a better way explain how yeast works than with belching sock puppets, I haven't seen it. After that, we moved onto the hands-on portion of the lesson. First, we tried setting out two mixtures of warm water and yeast, one with sugar and one without. Within fifteen minutes, it was clear that sugar is necessary to fuel the yeast, since the mixture with sugar was bubbling merrily away and the plain water mixture was sitting there tepidly. I had K look at the yeast foam and see the bubbles in it.
To further cement the idea that yeast gives off gas (and because it was really cool), we took a two-liter soda bottle, put warm water, yeast and sugar in it and then stretched a balloon over the top. Within half an hour, the balloon had popped up and was clearly inflated on top of the bottle. We could see the yeast foaming away at the bottom as well. We went out for several hours after that and when we came home, the balloon had gotten quite a bit larger and the yeast was clearly still working away, which really impressed me. Even though I've baked more than enough bread to know that yeast keeps working for hours and even days, it's still hard to carry that over to realize that the yeast really is a living organism that keeps eating and producing as long as it has food, even when it's not hidden in bread.
The final experiment of the day was to talk about other leaveners, specifically baking soda. Since baking soda is much more commonly used in making cakes in modern times, I wanted to show K how it worked. I suppose it wasn't so much an experiment as a demonstration: I put baking soda in the bottom of a glass and poured vinegar over it, and as everyone who ever made a baking sode volcano knows, it bubbled up quite impressively. To learn a bit more about making cakes and baking soda, we read The Magic School Bus Gets Baked in a Cake and watched an episode of the Magic School Bus tv show that covered pretty much the same story.
Then, of course, we had to bake a cake. At that point, we were done with science for the day since there was no recapturing K's interest when there was a cake to be decorated.
This week, I decided that right before Christmas is not the time to try to get a six-year-old to concentrate on school, so we're putting off the rest of Duchess until after we get back from Michigan. There's more than enough of the Middle Ages to fill a full week, and it will give me a chance to get some books that I had wanted but didn't have time to get through interlibrary loan. We will be doing A New Coat for Anna next week because K's grandmother will be visiting with her spinning wheel, and that's far too good an opportunity to give hands-on experience with fiber production from fleece to yarn to pass up. I don't think we'll have any trouble getting K to pay attention to the process of dyeing wool or spinning it, even with new Christmas presents to distract her.
Books used today:
The Duchess Bakes a Cake by Virginia Kahl
The Magic School Bus Gets Baked in a Cake by Joanna Cole