Theme: Food Science

Lesson: Bread Baking – Pretzels!!

Important Concepts: Yeast–produces the CO2 which makes bread spongy

Gluten – protein composite which gives bread its texture

Background: (courtesy of Wikipedia)

When dough made with wheat flour is kneaded, gluten forms when glutenin molecules cross-link to make a sub-microscopic network and associates with gliadin, which contributes viscosity and extensibility to the mix. If such dough is leavened with yeast, sugar fermentation produces bubbles of carbon dioxide which, trapped by the gluten network, cause the dough to swell or rise. Baking coagulates the gluten, which, along with starch, stabilizes the shape of the final product. Gluten content has been implicated as a factor in the staling of bread, possibly because it binds water by hydration.

The development of gluten (i.e., enhancing its elasticity) affects the texture of the baked goods. Gluten's attainable elasticity is proportional to its content of glutenins with low molecular weights because that fraction contains the preponderance of the sulfur atoms responsible for the cross-linking in the network. More development leads to chewier products like pizza and bagels, while less development yields tender baked goods. In general, bread flours are high in gluten while cake flours are low. Kneading promotes the formation of gluten strands and cross-links, so a baked product is chewier in proportion to how much the dough is worked. Increased wetness of the dough also enhances gluten development. Shortening inhibits formation of cross-links, so it is used, along with diminished water and minimal working, when a tender and flaky product, such as pie crust, is desired.

Activity:

  1. Before the kids arrive prepare the classroom by wiping down the tables and laying out long strips of wax paper for the kids to work on. You’ll probably only have to cover one of the two table per island. Tape the wax paper down over the edge of the tables.
  2. Have a tutor obtain some warm water from the teacher’s lounge and dissolve each pre-measured container of brown sugar (4 Tbsp) and yeast (1 Tbsp) in 1 cup warm water. (Save one to do when the kids arrive.) Let rise for a few minutes.
  3. Mix yeast, sugar and water with pre-measured flour (just less than 3 cups) and salt (1 tsp) and stir until consistency is even. (Again save one for when kids arrive.) Each batch is enough for one table of 4-5 kids.
  4. When the kids do show up, ask them to finish their snacks quickly and wash their hands.Once they’re done, introduce yourselves and the lesson. What’s the theme of the quarter? What did we do last week? Etc.
  5. This week we’re learning about bread. What’s a quality of bread you find appetizing? Crust, texture, flavor. What does the inside of a slice of bread look like? Lots of little holes.
  6. The holes in bread are caused by yeast.Show the un-dissolved yeast and sugar mixture. What is yeast? Type of fungi. Note that yeast is alive. How do we know?(Start mixing the yeast + sugar in the water.) What are characteristics of living things? Uses energy, disposes of wastes, reproduces, etc. As the yeast water mixture starts to bubble point out that the yeast is using the energy in the sugar (and later the flour) and producing a waste product CO2.
  7. Role of yeast is to produce the holes you find inside a slice of bread. This is the reason dough rises. Note the other key ingredient in bread: flour. Flour provides gluten which comprises the main structure of a bread loaf. Mix the yeast and water with the unused flour and salt.
  8. As it is mixed the dough goes from a watery to much a thicker and stickier consistency. That’s the gluten forming increasingly larger strands. Kneading the dough ensures gluten network is even and well formed giving bread its familiar texture.
  9. Divide up into groups by table, each table will knead their own dough. Start by showing the kids how to knead: Take the dough ball, flatten it with your palms by pushing down on it. Fold the dough onto itself. Rotate the dough 90 degrees and repeat. What are we doing? We’re making sure the gluten network runs throughout the entire dough. Be careful not to tear the dough while kneading as this destroys gluten chains.
  10. Divide up the dough so that each kid has their own to knead. This should take a fairly long time. The bulk of the lesson’s activity is just playing with the dough and kneading it.
  11. Eventually, have the kids roll their dough into long strands and tie them up in pretzel shapes. Give the kids a bit of wax paper to place their creations on and have them write their names on the paper so that we can return them the finished products once we have a chance to bake them.
  12. Clean up.