Abstract

Objective

To investigate the effect that fat and its temperature have on the taste and texture of pastry shells.

Introduction

Going to the bakery can be like a day in paradise. There is usually a display of delicious sweets and pastries to tempt the palate and the eyes. Many of these treats are made using wheat flour. Wheat flour is an interesting substance. When you mix water with other powdery substances, you just get a paste. But when you mix water with wheat flour, you get a very different material, and one that is the base for so many wonderful and tasty treats, such as breads, pasta, and pastries. Pie crusts (also called pastry shells) were developed in the Middle Ages, but not for fruits. They were actually first used to contain and preserve meat preparations, resulting in dishes like the Cornish pasty.

The taste and texture of breads, pasta, and pastries depends upon the makeup of the batter or dough. Batters and doughs are made up of water, gluten proteins, and starch granules. Glutens are chains of proteins, and when they are dry, the gluten protein chains don't react or move. When the gluten protein chains come in contact with water, however, they work together and can change their shape, either forming longer chains or breaking into smaller chains. This results in a substance that is both plastic (can change its shape) and elastic (bounces back and returns to its original shape). So though the dough can change its shape, it resists the change and tries to move back to its original shape. Gluten and water forms the network that gives bread its shape. Starch is also very important when making bread, for several reasons. It holds onto water and gives volume and structure to bread. It also makes its way through the bread and breaks up the gluten network, tenderizing it and giving it that light, delicate texture.

To make bread, you add water to flour to create a cohesive mixture of gluten and starch. In the case of a pastry, however, you add large amounts of fat to coat and separate the flour particles from each other, but you then add just enough water to make a dough. Since much of the starch in the flour is not in contact with any of the water, the resulting cooked dough is crumbly and flaky. The role of the fat in making a pastry is to give texture to the final product. Depending on the kind of fat used, the pastry will also have a certain flavor. Pastry chefs use various types of fats, like vegetable shortening, butter, or lard. Though they are all are fats, they have major differences. Vegetable shortening, such as Crisco®, is a blend of partially hydrogenated cottonseed and soybean oil, fully hydrogenated cottonseed oil, and soybean oil. The result of hydrogenation is an oil that is solid at room temperature. The "working" temperature range of vegetable shortening is 53°F–85°F. This means that it can be worked (kneaded or mixed) without getting too soft within this temperature range. The working range for butter, an animal-based dairy product, is 58°F–68°F. The working range for lard (which comes from the fat of a pig), is 58°F–75°F. Outside of the working range, the fat doesn't hold its shape, leaks oil, and just sticks to the dough.

To make a pastry shell, the water and fat are incorporated into the flour; the resulting dough is chilled, and then it is rolled out. Rolling allows the gluten to develop, and the pieces of fat and flour to flatten and create layers. Whether or not a pastry or a pie shell becomes flaky and tender depends on the kind of fat used, and the temperature at which it is incorporated into the flour. In this cooking and food science fair project, you will determine which type and temperature of fat produces the flakiest and most-tender pastry shell. You will make pastry shells using vegetable shortening, cold butter, and melted butter; then you will compare the textures. Who knows, once you have figured out the best recipe, you might become your family's pie master!

Terms, Concepts, and Questions to Start Background Research

• Gluten
• Protein
• Plastic deformation
• Elastic deformation
• Starch
• Fat
• Hydrogenate

Questions

• What is the gluten content of different types of flour? What type is the best to use for pastries and why?
• What does salt do when added to dough?
• What percentage of butter is water? What effect does too much water have on a pastry?

Bibliography

• McGee, Harold. On Food and Cooking: The Science and Lore of the Kitchen. New York: Scribner, 2004.
• Prejean, W. Baking and Baking Science: Pies Including Ingredient Functions, Pie Doughs and Pie Fillings, Plus Mixing and Make–Up Demonstrations. Retrieved July 13, 2009, from http://www.bakingandbakingscience.com/pies.htm.

Materials and Equipment

• Bowl, large and ceramic
• Flour (16 cups, plus a little more for dusting the rolling pin and rolling surface)
• Kosher salt, not table salt (6 teaspoons)
• Measuring cup, 1-cup
• Measuring cup, 1/3-cup
• Fork
• Teaspoon
• Pastry blender or 2 dinner knives. Pastry cutters can be purchased from your local home goods store.
• Vegetable shortening, (1 1/2 cups). Purchase the shortening in individually wrapped sticks. This makes it easy to measure the required amount.
• Stopwatch
• Butter (4 1/2 cups). Purchase the butter in individually wrapped sticks. This makes it easy to measure the required amount.
• Tablespoon
• Ice water
• Plastic wrap (1 roll)
• Rolling pin
• Large, clean, flat surface to roll out the pastry shell
• Ruler
• Pie plate, 9 inches wide
• Oven mitt
• Hot pad
• Pot, 1-quart (qt.)
• Volunteers (2)
• Lab notebook
• Graph paper

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Experimental Procedure

Preparing Your Pastry Shells

1. Wash your hands and make sure all your cooking equipment is clean.
2. Measure 1 1/3 cups of flour and place it into the large bowl. Measure 1/2 teaspoon of kosher salt and mix it completely into the flour with the fork.
3. Add a 1/2 cup of vegetable shortening to the flour mixture and use the pastry blender to work the shortening into the flour. If you do not have access to a pastry blender, then you can use two dinner knives to "cut" the shortening into the flour. You should blend and cut the shortening into the flour for approximately 7–10 minutes. The result should be gravel-size pieces of fat-coated flour. Do not use your hands to cut the shortening into the flour, because the heat from your hands will affect the fat.

Figure 1. Flour with fat blended into it. The result is gravel-size pieces of fat and flour.

4. Once the flour mixture is the right texture, add 3 tablespoons of ice water to the bowl. Use the fork to blend the water into the flour mixture.
5. Once the water is completely blended into the flour mixture, quickly gather the dough into a ball and flatten it into a 4-inch-wide disk with your hands. Use your ruler to measure. Wrap the dough with a piece of plastic wrap and put it in the refrigerator for 30 minutes. Use the stopwatch to keep track of time.
6. After 30 minutes, remove the dough from the refrigerator and unwrap the plastic wrap. Preheat the oven to 425°F.
7. Lightly flour the rolling pin and the rolling surface. Roll the disk from the center out, in each direction, forming a 12-inch circle. Use a ruler to measure how large the circle of dough is.
8. Transfer the dough to the 9-inch pie plate and gently press the dough against the bottom and sides of the pie plate.
9. Trim any dough that is hanging over the edge of the pie plate with a knife. Prick the bottom and sides of the dough with the fork to prevent the bottom of the crust from blistering and puffing up.
10. Place the pie plate into the preheated oven. Bake the pastry shell for about 15–18 minutes. Use the stopwatch to keep track of time. Once the time has elapsed, put on the oven mitt and remove the pie plate from the oven. Place the pie plate on a hot pad. The pastry shell should be golden brown. Let the pastry shell cool completely and carefully remove it from the pie plate. You should have a helper assist you with this step. To remove it, you might want to turn the pie plate upside-down with one hand, while holding the pastry shell with the other hand, to catch it. Set it aside.
11. Thoroughly clean and dry all of your cooking equipment.
12. Repeat steps 1–11 using a 1/2 cup of butter from the refrigerator, in place of the vegetable shortening.
13. Make sure to keep track of which method was used for each pastry shell.
14. Repeat steps 1–11 using a 1/2 cup of butter at room temperature. Take the butter out of the refrigerator and let it sit at room temperature for 1 hour before using it.
15. Now melt a 1/2 cup of butter in the small pot on the stovetop. Repeat steps 1–11 using the melted butter. Remember to keep track of which method was used to produce each pastry shell.

Testing Your Pastry Shells

1. Compare the pastry shell made using shortening, the pastry shell made using cold butter, the pastry shell made using the room temperature butter, and the pastry shell made using melted butter in your lab notebook. Make note of the following: What color is the shell? What happens when you cut through the bottom with a knife? Does it shatter into pieces?
2. Now bring in your two volunteers and all of you should compare the pastry shells. Record their observations in your lab notebook in a data table, like the one shown below. Have each volunteer comment on the following: Taste a piece of the shell. Is it tender? Is it flaky, sandy, or chewy? Devise a ranking scale for tenderness and flakiness so that you and your volunteers can compare the pastry shells objectively. For example, you could have a scale of 1–3 to describe the tenderness and the flakiness.

3. Repeat the entire cooking and testing procedure two additional times. Remember to record all of your observations in your lab notebook.

Analyzing Your Data

1. Analyze the data. Average the tenderness rankings for the trials for each volunteer and for each type of fat used. Then average the flakiness rankings for the trials for each volunteer and for each type of fat used. Plot the data on graph paper, or if you would like to do your plots online, you could use the following website: Create a Graph. Label the x-axis Type of Fat and the y-axis Average Ranking and then plot the data for all of the volunteers
2. At the end of this science fair project, use the best recipe and bake a delicious pie!

Variations

• Using a microscope, investigate the physical differences between the three pastry shells. Can you see any differences looking through the microscope?
• Does using lard make a good pastry shell? How does a lard-based pastry shell compare to the shells made from shortening and butter?
• Remove the chilling the dough step from the procedure. Is chilling the dough required to make a good pastry shell?
• Experiment with how baking temperature affects the pastry.
• What happens to the texture of the pastry shell if you knead and work the dough by hand? How is the texture affected if, instead of blending the fat and the flour by hand, you use a food processor?
• For another Science Buddies science fair project about gluten, try Great Globs of Gluten!.

• For more science project ideas in this area of science, see Cooking & Food Science Project Ideas.

Credits

Michelle Maranowski, PhD, Science Buddies

• Crisco® is a registered trademark of The J.M. Smucker Company.

Last edit date: 2009-06-16 09:30:00