September 1, 2016
6 min read
The Scientific Secret of Stretchy Dough
A science activity for bakers, from Science Buddies
By Science Buddies
Key conceptsChemistryFood scienceProteinElastic
IntroductionDo 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!
BackgroundWheat 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.
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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.
Ready to test 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!
Materials
Vital wheat gluten (This is available in well-stocked grocery stores or health food stores.)
Wheat flour (Bread flour is preferable, but any wheat flour is fine.)
Gluten-free flour (This could be rice flour, corn flour, a gluten-free baking flour mix, etcetera.)
Salt
Half-cup dry measuring cup
Mixing bowl
Tablespoon measuring spoon
Spoon
Water
Clean work space
Preparation
Choose a work space that is easy to clean and can take some water spills.
Get all of your ingredients out and ready to use.
Procedure
Combine a pinch of salt with one half cup of vital wheat gluten in your mixing bowl. Add three tablespoons of water and mix, first with the spoon, then with your hands. Add one or two more tablespoons of water, if needed, until the flour sticks together and forms a nice soft ball. It should have the consistency of play dough. Place the ball on a clean spot on your work space.
Clean your mixing bowl and measuring utensils then repeat the previous step with one half cup of wheat flour and then again with one half cup of gluten-free flour. How do the different flours feel? Does one stick together better than the other?
Knead your gluten dough for three minutes. To knead, start by flattening the ball of dough a little. Then fold the dough over itself and flatten as you end the fold. Give the dough a quarter turn and repeat the folding, flattening and turning.
Repeat the previous step with the wheat flour dough and the gluten-free dough. Are some doughs easier to knead than others? You might notice that some doughs fall apart as you try to knead them. If so, just take note and skip kneading that dough.
Let your dough balls rest for one half hour.
While you wait, look at the nutritional content label of the flours printed on the packages. Which one has more carbohydrates per one quarter-cup serving, and which one has more protein?
In a moment you will test how elastic the doughs are and how easily they can be stretched.
Elasticity measures how well a material recovers its original form after a deformation. Which dough do you expect to be elastic, meaning it bounces back after you punch it? Which dough do you expect to be starchiest? Do you expect you will be able to stretch any of the doughs paper-thin?
Now that you have given the gluten network in the doughs some time to develop, you can put them to the test. Lightly punch your balls of dough—all three with the same force—to evaluate their elasticity. Do you see signs of elasticity in any of your doughs?Can you rank them from most elastic to least, or nonelastic?
A second characteristic is stretchiness. A dough that stretches well can trap gas bubbles, providing well-risen, fluffy baked goods. Take a ball in two hands and stretch it out between your hands. Does it stretch easily or does it break instantly? Do you need to apply force to get it to stretch out or does it stretch readily? Do this with all three doughs.
Some pastries require a paper-thin layer of dough. How thin can you stretch out or roll out your doughs? Can you make any of them so thin that you can almost look through them?
Looking at your test results, what type of baked good would each dough be good for: cake, cookies, bread, etcetera? Why do you think this is the case?
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. 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 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.
Observations and resultsWas the gluten dough elastic and stretchable? Did the gluten-free dough fall apart, showing neither elasticity nor stretchiness? This is expected; 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 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!
More to exploreThe Scientific Secret of Fluffy Pancakes, from Scientific AmericanSingle-Celled Science: Yeast Beasties, from Scientific AmericanGreat Globs of Gluten! Which Wheat Flour Has the Most?, from Science BuddiesThe Goo on Gluten, from Science Buddies
This activity brought to you in partnership with Science Buddies
