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Aug. 10, 2010

Cooking with Chemistry

by Science Friday Education

Click to enlarge images
Food science and technology are the study and development of tasty, nutritious, safe and convenient foods. In this SciFri Video, Chef Dufresne experiments with various methods to create new dishes. However, anyone who experiments in his or her kitchen by creating recipes or mixing ingredients is using food science.
 
In this activity, students will experiment with different variables in making hollandaise sauce to achieve the correct texture and consistency. Students will learn about immiscible liquids and how to use emulsifiers to create a stable and homogenous mixture using these particular liquids.
 
Grade Level: 6th – 8th grade
Subject Matter: Chemistry
National Standards: NS. 5- 8.1, NS.5-8.2
Chef Wylie Dufresne, the owner of New York City restaurant wd~50, experiments with food, literally. He has lab notebooks detailing what certain chemicals do to certain dishes. One of his signature dishes is a spin on eggs Benedict: he found that creating the plate's centerpiece--a cube of fried hollandaise sauce--required a lot of scientific testing. Science Friday stopped in at Dufresne's kitchen to see how he prepares the dish.
 
Activity Materials
Oil
Water
Food coloring
Small plastic bottles, one for each student
Measuring spoons
Dishwashing liquid
Glass jars, one for each student
Stove or hot plates, one for each student
Wire whisks, one for each student
Oven mitts, one pair for each student
Saucepans (stainless steel, enamel or glass), one for each student
Hollandaise sauce recipe: one copy for each student, a set of the following ingredients for each student
4 egg yolks
1 tablespoon lemon juice
1 tablespoon cold water
¼ teaspoon salt
1 ½ sticks of butter (to make 1 cup of clarified butter)
Pinch of white pepper
 
Vocabulary
Homogeneous: Having a uniform composition or structure.
Immiscible: Liquids that cannot be mixed or blended together to form a homogenous substance. Examples are oil and water.
Emulsion: A stable, homogeneous combination of two or more immiscible liquids.
Emulsifier: An agent used to assist in the dispersion of two or more liquids to produce an emulsion.
Polar molecule: A molecule with positively and negatively charged ends.
Non-polar molecule: A molecule with an even distribution of charge all around.
 
What To Do
  1. Begin the lesson by having the students watch the Science Friday Video, “Stovetop Science – Frying Hollandaise.” Ask students to explain how cooking involves science. Tell students that they will explore what happens when you try to mix immiscible liquids together, and how you can use science to make the perfect hollandaise sauce.
Activity 1
  1. Hand out a small plastic bottle, half-filled with water, to each student. Have students add a few drops of food coloring to the water. Observe how the food coloring reacts with the water. With the top on, shake the bottle gently. What happens to the water?
  2. Have students add two tablespoons of oil to the bottle. Observe and describe how the oil reacts with the colored water.
  3. With the top on, have students shake the bottle vigorously for 30 seconds. Ask students to predict what will happen to the liquids.
  4. Set the bottle on a flat surface and observe for five minutes what happens to the mixture. Have students discuss their observations. Why do they think food coloring and water are able to mix together-- but not the oil and water?
  5. Have students add a few drops of dishwashing liquid to the bottle. How did the oil react to the dishwashing liquid? What do they think will happen if they shake the bottle and observe the mixure for five minutes?
  6. Review with students the definitions of immiscible liquids and emulsifiers. Which liquid was immiscible and which was the emulsifier?
Activity 2
  1. Before starting the second activity, make sure each student’s work area and cooking equipment are clean. Review the importance of following proper safety guidelines for handling kitchen equipment and utensils.
  2. Hand out to each student all necessary ingredients listed in the hollandaise sauce recipe. Based on the ingredients that they have and after observing the SciFri Video, what procedure do they think they should follow to make hollandaise sauce?
  3. Have students place one cup of butter in a small saucepan over very low heat until it melts completely. Ask students to observe and describe the butter as it melts. How does its physical properties change?
  4. Tell students to wait for the butter to melt into a clear yellow liquid, in between a layer of foam floating on top and milky liquid at the bottom. The clear yellow liquid is called clarified butter. Clarified butter is pure butterfat (butter without the milk solids and water). What do they think are the advantages to cooking with clarified butter?
  5. Remove the saucepan from the heat and have students skim off and discard all the foam. Pour the clear yellow liquid (clarified butter) into a glass jar. Set the clarified butter aside and keep it warm until it is needed again.
  6. In a clean saucepan, whisk four egg yolks and one tablespoon of water. Add one tablespoon of lemon juice, ¼ tablespoon of salt and a pinch of pepper. Whisk until thoroughly mixed and the eggs are slightly thickened.
  7. Place the saucepan over low heat and continue whisking until it has a smooth and creamy texture resembling heavy cream. Why do they think it is necessary to continuously whisk the egg mixture?
  8. Remove the pan from the heat. Have students whisk in one teaspoon of the clarified butter at a time. What do they think will happen if they pour all the butter in at the same time?
  9. Tell students to continue whisking in the butter until the sauce has a light and smooth consistency. What do they think would happen if they continued whisking the sauce? How would the consistency change?
  10. Have students compare and contrast their hollandaise sauce. What variables could have caused any differences in texture?
  11. Optional: Students may taste their hollandaise sauce or serve it over bread or vegetables. Hollandaise sauce is served warm, not hot. Keep the sauce warm by placing it over a pan of lukewarm water. For health reasons, do not serve more than an hour after making.
What’s Happening?
While water can mix with other liquids to form solutions, oil and water are two immiscible liquids that do not mix. This is because water molecules are polar and oil molecules are non-polar. Each similar type of molecule will group together instead of bonding with molecules of a different polarity. Vigorously mixing the oil and water will create a temporary solution until the oil, which has the lower density, floats to the top.
 
In the first activity, the dishwashing liquid acted as an emulsifier because dishwashing liquid molecules are attracted to both oil and water molecules. Therefore, dishwashing liquid molecules will stabilize the bond between the water molecules and the oil molecules.
 
In the second activity, two of the ingredients, butterfat and water, also are immiscible. So an emulsifier must be added to create a smooth and creamy sauce. Egg yolk contains proteins and other molecules that act as emulsifying agents. These proteins are attracted to oil molecules and water molecules. Whisking the butter in gradually breaks down the butter into tiny drops that can be coated by the emulsifying agent in egg yolks. The slower the butter is poured, the smaller the coated drops will be, resulting in a lighter, smoother sauce. Pouring all the butter in or not whisking sufficiently will result in a “broken” sauce – a sauce in which the ingredients are separated or clumpy. There are many variables that can affect the consistency and texture of hollandaise sauce. These include maintaining even heat distribution, the rate of whisking, and the proper mixing of ingredients.
 
Topics For Science Class Discussion
  • What were the two emulsions created when making hollandaise sauce?
  • What function does the lemon juice serve in making hollandaise sauce, other than adding flavor?
  • What are the different types of emulsifiers found in eggs?
  • Will the hollandaise sauce remain an emulsion if stored or refrigerated overnight?
Extended Activities and Links
  • Emulsifiers are found and used in many everyday products, from hand creams to salad dressings. Have students research the different types of emulsions and what is the emulsifying agent in each one.
  • Have students design an experiment to test which type of emulsifier works best to stabilize an oil-in-water emulsion.
  • Food scientists research and develop new food products, and test the nutritional value and quality of foods. Assign students the role of a food scientist and have them develop a new food product or improve the quality or nutrition of an existing food product.
  • Test the emulsifying agent found in egg whites
  • Make mayonnaise, another commonly used emulsion

 

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