Introduction
Do you remember the last time you baked cookies, bread or cake? Did your baked good turn out perfectly? Or was it a bit too flat or perhaps rubbery and tough, or maybe with clumps of dry ingredients? The problem might have been in how you mixed the dough—or with the type of flour you used. In this science activity you will knead, stretch and punch some pretty remarkable doughs and discover what provides structure and elasticity to your baked goods. Next time you prepare dough for bread, pizza, cookies, cake, pie or any other baked good, you'll know what to do!
Background
Wheat flours mainly consist of carbohydrates and protein, with some fiber. They are classified according to their gluten (or protein) content for a good reason. Getting the right portion of gluten (the protein that naturally occurs in wheat) is essential to getting the right texture in your baked goods. Wonder why? From the moment you bring a liquid ingredient (such as milk or water) in contact with wheat flour, the individual gluten proteins in the flour unravel and hook onto one another, creating strong bonds. With time, an elaborate network of interconnected gluten strings forms. This network holds the dough together, giving it its structure.
Kneading the dough slowly unfolds the entangled network and aligns the long gluten strings in a stretchy, layered web. A pinch of salt helps as well because it neutralizes electrically charged parts of the gluten, allowing them to better slide along one another. The result is an elastic, stretchable dough that traps gas bubbles. Sometimes a dough can be stretched so thin it becomes translucent, making the network of gluten visible with a magnifying glass or microscope. It is the absence of this intricate gluten network that makes gluten-free baking a challenge.
Elasticity measures how well a material recovers its original form after a deformation.
A second characteristic is stretchiness. A dough that stretches well can trap gas bubbles, providing well-risen, fluffy baked goods.
Extra: What would happen if you let the doughs rest for a longer period of time? Would the elasticity or stretchiness increase? Place your doughs in a container or plastic bag and let them rest for a few hours or overnight. This allows the flours to fully absorb the water and the gluten networks to fully develop.
Extra: Place each dough ball in its own bowl, cover each with water and let them soak awhile. Play with each ball; pinch and knead it a little and see what happens. Carbohydrates will wash out whereas the gluten network will create an elastic ball. After washing away all the carbohydrates, what do you think will be left in each type of dough? Try it out and see if your prediction was correct.
Extra: Yeast is a live, single-celled organism that feeds on carbohydrates and provides gases that make a yeast dough rise. In which dough(s) do you expect yeast to be most active: gluten flour, wheat flour or gluten-free? The activity “Yeast Alive! Watch Yeast Live and Breathe,” from Scientific American can help you create your test. Feed the yeast with water–flour mixtures, let it sit for awhile and see if your yeast colony flourishes.
Extra: Gluten has several functions in a dough. It binds ingredients and provides structure to the dough. It creates elastic doughs that do not need a mold to keep their form. It also helps retain moisture and prolongs the shelf life of the baked goods. Gluten-free dough mixes use xanthan gum, guar gum and/or ground seeds to take over these tasks. Can you bake a gluten-free bead and a wheat bread and compare their performance against these parameters? You can also bake two wheat breads, one with cake flour (low in gluten) and another with bread flour (high in gluten) and compare their performance against these parameters.
Combine gluten and water, and a network of long, unorganized, knotted gluten strings will form. Kneading aligns these strings, creating a dough you might be able to stretch so thin you can almost see through it. The more gluten, the more elastic, stretchy and strong the dough will be. Mixing gluten and water results in a dough that almost feels like rubber. Wheat flour contains 6 to 12 percent gluten, enough to provide a gluten network that holds the carbohydrates together. This dough is elastic and stretchy, but not as strong and tough as the gluten dough. A gluten-free dough, on the other hand, is crumbly; it falls apart easily. Bakers add ingredients such as xanthan gum, guar gum and/or ground seeds to keep the baked goods together—but making a gluten-free version of some fine pastries, fluffy croissants and delicate wheat breads can be challenging!
https://www.scientificamerican.com/article/the-scientific-secret-of-stretchy-dough/
Balancing the Elasticity and Extensibility of Your Bread Dough
Developing dough with sufficient strength is essential to creating high-quality bread. Here are some tips to help you achieve the proper dough strength in your breads.
Dough strength is a balance of two main properties—extensibility and elasticity. The gluten, which forms when the flour interacts with water, is what lends the dough these two characteristics. Extensibility is its ability to be stretched. Elasticity is its ability to go back to its original shape. Strong dough is not very extensible but very elastic. Weak dough is very extensible but not very elastic.
Dough strength affects production characteristics through all of the baking process. For example, strong dough isn't suitable if you want it to ferment for long periods—because it will overdevelop as it ferments. But dough strength is most critical during shaping. If the dough is too strong, it will be too elastic and difficult to shape— especially into long loaves like baguettes. If it's too weak, it will stretch easily, but won't hold its shape during proofing—a problem in panless hearth breads where the dough must be strong enough to support itself.
Having the right proportion of water in your formula allows you to achieve the right balance. A lower water ratio produces stronger dough. A higher water ratio produces a weaker, but more stretchable dough. Artisan bread doughs need sufficient strength as well as sufficient extensibility.
Incorporating an autolyse is one way to increase dough extensibility without sacrificing strength. An autolyse allows the flour and water to rest for 15 to 45 minutes before adding the remaining ingredients. It gives the flour (especially the protein) time to fully absorb the water, so the gluten can form better, more complete bonds. During the autolyse, protease enzymes in the flour work to slightly break down the gluten, providing more extensibility to the dough without added water.
http://www.progressivebaker.com/tips_tools/balancing_elasticity.html