The Scientific Secret of Stretchy Dough
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!
This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.
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 (like milk or water) in contact with wheat flour, the gluten in the flour unravel and hook onto each other, 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, because it neutralizes electrically charged parts of the gluten, allowing them to better slide along each other. 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.
Ready to experiment and measure your strength against some incredibly stretchy dough? Once you’ve explored the dough, you’ll be ready to bake up a perfect treat!
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 network to fully develop. Perform your tests again. Do you notice considerable changes?
Extra: Place each dough ball in its own bowl, cover each with water and let them soak. Play with each ball; pinch and knead it a little and see what happens. Carbohydrates will wash out, while 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 living single-celled organism that feeds on carbohydrates and provides the gasses that make a yeast dough rise. In which dough(s) do you expect the yeast to be most active: the gluten-flour dough, the wheat-flour dough or the gluten-free dough? 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 a while 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. Besides, it 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.
Observations and Results
Was the gluten dough elastic and stretchable and did the gluten-free dough fall apart, showing no elasticity nor stretchiness? This is expected, as it is the gluten network that holds a dough together and gives it elasticity and the ability to stretch.
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 gives 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 like xanthan gum, guar gum and/or ground seeds to keep the baked goods together, but haven’t succeeded yet in creating a gluten-free version of some fine pastries, fluffy croissants and delicate wheat breads.
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Sabine De Brabandere, PhD, Science Buddies
Science Buddies |
Gluten, protein, carbohydrates, elastic
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