Abstract
Close your eyes for a moment and think about your favorite cake, pasta, and crusty bread. OK, you can open your eyes now, and please do not drool on your computer! What was the cake you pictured like? Was it light and fluffy? Did you imagine pasta with a silky, smooth texture? Was the bread you pictured wonderfully chewy? Did it give your jaws a workout? In this science fair project, you will explore an amazing substance in these foods, called gluten, and discover why these foods, all made from wheat flour, have such different levels of tenderness and toughness.Summary
Kristin Strong, Science Buddies
This science fair project follows many of the materials and part of the procedure outlined at the following source:
- Exploratorium Contributors. Goodness Gracious! Great Ball of Gluten! The Exploratorium. Retrieved September 21, 2008.
Objective
To determine the relative differences in gluten content between different types of flour.
Introduction
Breads, bagels, pastas, cakes, cookies, crackers, muffins, pastries, pies, and pizza crusts. Are you hungry yet? What do all these foods have in common? Traditionally, they are all made from wheat flour , the fine powder made from grinding and sifting kernels of wheat, which are the edible part, or fruit , of the wheat plant. Wheat (which is shown in Figure 1, below) is one of a small number of cereal grains that comes from the 8,000 species of plants in the grass family. It first grew wild on the high plains of the Middle East, and then about 10,000 to 12,000 years ago, people in this area first began to cultivate it. Today, it is the third most produced cereal grain in the world (corn is first, and rice is a close second with wheat).
Figure 1. This drawing shows wheat, from the grass family of plants.
Why is wheat flour so popular? Well, when you mix water with most other flours (like those made with the cereal grains mentioned above), what you get is a ball of paste that sort of sits there. Mix wheat flour with water, though, and gradually, under repeated pressure, it transforms into something quite lively. It is both plastic (can change its shape), and elastic (bounces back and returns to its original shape). These unique qualities allow wheat dough to trap gas inside and expand, kind of like a balloon, but not to the point of breaking. The gas comes from tiny fungi called yeast, which give off carbon dioxide. The gas can also come from the combination of acids and bases in the dough. This expansion of the dough helps breads and other baked goods rise and become light and fluffy.
The plasticity and elasticity are made possible by the presence of an amazing composite of proteins within the wheat kernel, called gluten. These proteins in gluten are long chains of amino acids, some of the longest in the world, in fact, with chains around 1,000 amino acids long! The two major proteins in gluten are called gliadins and glutenins. The gliadins (think of the word "glide") give the gluten its plasticity because they act kind of like ball bearings or a lubricant. They allow the other major protein, the chains of glutenins, to slide past each other without forming bonds. You can think of the glutenin molecules as long spring-like chains. As the dough is worked and kneaded, these glutenin molecules can link up with each other, end to end, to form super-long, spring-like chains. This makes a tight, coiled mesh, or net, called "the gluten," to trap the gas in, and this gives the dough its elasticity. All those springs want to "spring back" when they are stretched!
Gluten is also available in a few other cereal grains, notably rye and barley, but in lesser quantities than in wheat. Wheat flours also vary in the amount of gluten they contain. Hard wheat is high in gluten and is good for baking things that need toughness and strength, like yeasty breads, bagels, and puff pastries. Soft wheat is low in gluten (high in starch) and is better for baked goods that need to be tender, like pancakes, cookies, and pastries.
Besides the type of flour that a baker chooses, he or she can also control the gluten strength by manipulating the dough, or by adding other substances to the dough. For example:
- Kneading or stirring the dough strengthens and organizes the gluten mesh.
- Adding salt also greatly strengthens the gluten mesh.
- Adding sugar limits the development of gluten.
- Adding acids weakens the gluten mesh.
- Adding fats weakens the gluten.
Legend has it that gluten was first discovered in the 7th century by Chinese Buddhist monks who were looking for a substitute for meat in vegetarian cooking. When a ball of wheat dough is placed in a bowl of cold water and then kneaded, the starch in the dough gradually falls away and dissolves in the water, leaving behind a stringy, insoluble ball, most of which is gluten. The Chinese people call it "the muscle of flour." This high-protein mass can then be cut into pieces and fried, steamed, or baked. It has a chewy, meat-like texture. Even today, on a commercial scale, this cold-water rinse-and-knead method is the process by which gluten is commonly extracted from wheat flour. In this food science project, you will use this gooey, sticky process to find out which types of wheat flour contain the most and the least gluten. You will discover that gluten comes from the Latin word for glue for good reason!
Terms and Concepts
- Wheat
- Flour
- Kernel
- Fruit (of a wheat plant)
- Cereal grain
- Grass family
- Cultivate
- Plastic
- Elastic
- Yeast
- Carbon dioxide
- Acid
- Base
- Composite
- Protein
- Gluten
- Amino acid
- Gliadin
- Glutenin
- Bond
- Hard wheat
- Soft wheat
- Starch
- Knead
- Insoluble
Questions
- What are the properties of gluten, and what proteins within gluten are responsible for those properties?
- How can a baker control the strength of gluten?
- What are the different types of flour and what kinds of baked goods are they best for?
Bibliography
- McGee, Harold. On Food and Cooking. New York, NY: Scribner, 2004.
This source describes the physical properties of gluten, where it is found, how it is used, and the health concerns associated with it:
- Wikipedia Contributors. (2014, October 27). Gluten. Wikipedia: The Free Encyclopedia. Retrieved October 31, 2014.
This source describes the many types of flours, and their relative gluten content:
- Wikipedia Contributors. (2014, October 11). Flour. Wikipedia: The Free Encyclopedia. Retrieved October 31, 2014.
Materials and Equipment
- Flours, made from wheat, such as whole wheat bread flour, pastry flour, cake flour, or all-purpose flour (3 different types)
- Small mixing bowls (3)
- Sticky notes
- Measuring cup, 1-cup size
- Fork
- Cutting board or work surface
- Clock or watch
- Strainer with small holes
- Ruler
- Lab notebook
Experimental Procedure
- With the measuring cup, measure out 1 cup of each type of flour into its own small mixing bowl, as shown in Figure 2. Examine the flours and note any differences in color and feel. Write down your observations in your lab notebook.
- If you have trouble telling the flours apart, then label your bowls with sticky notes to identify what type of flour is inside.
Three small bowls with pastry flour, all-purpose flour, and whole wheat flour. Each flour mixture has a different color and texture.
Figure 2. This photo shows three examples of different types of wheat flour.
- Select one bowl to begin with, and slowly add 1/2 cup to 3/4 cup of tap water to the bowl, while carefully stirring with a fork, as shown in Figure 3. It will seem difficult to stir at first, but will gradually begin to come together to form a rough ball.
Figure 3. This photo shows the gradual addition of water to the flour, while stirring with a fork to form a rough ball.
- Sprinkle a spoonful of flour (of the type you are working with) onto a work surface, and onto your hands as well, so that both are lightly dusted with flour. Place the ball of flour onto your work surface and knead it for approximately 5-7 minutes, until it becomes smooth and elastic. Use a clock or watch to keep track of the approximate time you spent kneading. Note the amount of time you spent kneading in your lab notebook so you can knead for the same amount of time in later trials.
- If you are unfamiliar with kneading, this is the process of pressing down on the dough ball with your palms, and then pulling it back up again and rotating it slightly with your fingertips, as shown in Figure 4, below. This cycle is repeated over and over again.
Figure 4. These photos show the pushing and pulling process of kneading.
- Repeat steps 3–4 for your other two bowls of flour. Be sure to knead all the flours for the same amount of time. At the end of the kneading process, you should have three smooth-looking elastic balls of dough. (Note that some flours will form better, firmer balls than others.)
- Place your three balls of dough back in their small bowls, as shown in Figure 5, and let them rest and relax for about 10 minutes.
Figure 5. This photo shows how the balls of dough will look after kneading.
- Now it is time to find out how much gluten is inside those balls of dough. If you thought kneading was icky and gooey, brace yourself for the next step! Place your strainer in the sink. Some strainers are "stand-alone," meaning they have legs to support them inside the sink, while others need to be placed over a bowl or propped against the edge of the sink. Either way, make sure your strainer is over a sink where the faucet can reach it.
- Take one of the balls of dough to the sink and cup it in your hands over the strainer. Let cold water run on it as you gently pull and stretch it apart, as shown below. The water will wash away the water-soluble parts, like the carbohydrates, but will leave behind the insoluble protein, the gluten, that you developed while you were kneading. The starch that is being washed away will look like a milky liquid. Continue rinsing your ball of dough until very little milky liquid is coming out and only a sticky, stringy ball remains.
Figure 6. These photos show how to rinse off the ball of dough inside a strainer.
- Rinse off your strainer to remove any debris, and repeat step 8 for the other two balls of dough. At the end of the rinsing process, you should have three balls of gluten (although, depending on the type of flour you used, a lot of the ball may have been washed away).
- Measure the diameter of each ball of gluten with a ruler. Record your measurements in a data table (like Table 1, below) in your lab notebook.
Figure 7. This photo shows the measurement of the diameter of one ball of gluten.
- Repeat steps 1–10 two more times so that you have a total of three trials for the three different types of flour.
- Average the diameters of your balls of gluten for each type of flour and record the averages in your data table. Which type of flour produced the smallest diameter gluten ball, on average? Which produced the largest? Does this make sense based on the type of foods that each flour is used to create?
| Flour Type | Pastry Flour (example) |
All-purpose Flour (example) |
Whole Wheat Flour (example) |
|---|---|---|---|
| Trial 1: Gluten Ball Diameter (cm) | |||
| Trial 2: Gluten Ball Diameter (cm) | |||
| Trial 3: Gluten Ball Diameter (cm) | |||
| Average Gluten Ball Diameter (cm) |
Ask an Expert
Variations
- You can bake your gluten balls by putting them in the oven at 450° Fahrenheit for 15–30 minutes. How do the gluten balls look, feel, and taste after they have been baked?
- Use a kitchen scale, such as the Fast Weigh Digital Pocket Scale, 500 by 0.1 G, available from Amazon.com, to evaluate the gluten balls, based on weight, rather than diameter.
- Choose one type of flour and create three equally sized balls of dough from it with different degrees of kneading: no kneading, 5 minutes of kneading, and 10 minutes of kneading. Rinse the three balls of dough and evaluate the gluten balls that are created, either by weight or by diameter.
- Select one type of flour and make doughs with different additives, such as salt, sugar, or oil. Compare the development of gluten within these doughs.
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