Some Science of Bread

In the 90s, I inherited a bread machine from my father. One of the first automatic bread makers, it resembles R2D2 and produces a cylindrical loaf, an absurdity for kids who know that all bread is square. The bread it produces is airy, and even if I remove the dough and bake it in an oven, the texture is not the same as a hand-kneaded loaf. But it’s always nice to set the timer before bed and wake to the smell of fresh bread, especially in winter.

Recently, we were down to our last two heels and it was snowing. Driving in snow for a loaf of bread seemed stupid so I pulled out the bread machine. I don’t use it enough to remember recipe measurements, but I thought I did. I added too much water and compensated by adding more flour. I watched the kneading cycle and all seemed well. The dough looked as dough should look when you set it aside to rise. What didn’t occur to me was that I’d altered the volume of the recipe and the machine’s recipes are fine tuned to match the capacity of its baking tub. The finished loaf filled the glass dome of the machine and resembled a huge muffin.

My son who shuns crusts but loves muffin tops (explain this to me) ate the top. It was big enough to wear, like the leather helmet George Clooney wears in Leatherheads. I was surprised how high the bread had risen.  I hadn’t added extra yeast. Wondering about this little disaster got me thinking about the chemistry of bread baking and one of my first internet stops was San Francisco’s Exploratorium. The Exploratorium’s Science of Cooking has a section devoted to bread.

In the section Bread Science 101, bread is reduced to its basics: a mixture of milled grains and water. What distinguishes a flat bread from what we generally use to make PBJs is leavening. Leavening agents can be baking soda or baking powder, which create a chemical reaction releasing carbon dioxide, or yeast, a living organism, which also releases carbon dioxide.  Of course, yeast’s gas release is much slower than baking soda. No one will launch a makeshift rocket with yeast.

Every kid with an old soda bottle is familiar with “experiments” with baking soda and vinegar, but yeast is another story. For a simple demonstration of yeast activity, a soda bottle and a balloon will serve.

Students can make their own yeast using two methods, one with flour and water and one starting with raisins or other dried fruit.

Bread as well as yeast can provide material for experiments. Students can test for the presence of glucose and starch and build a simple calorimeter to measure calories in bread and other foods.

A slice of bread can provide evidence of the presence of molds and reinforce the wisdom of hand washing.

If your school has a home economics program with an oven or ovens, baking bread, especially bread made with student-grown yeast, would add another dimension.

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