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Cooking Up Science
by Laurisa White Reyes
 
Turning the kitchen into a classroom is common enough. I often hear of homeschoolers using recipes as math lessons. At one time, public schools included cooking in home economics. Young cooks can even learn about world culture through cooking. But the one subject that is the very heart of cooking is the one about which I hear very little. The fact is, the kitchen makes for a perfect laboratory for the study of science and can be taught on many different educational levels. Young children can come to understand how applying heat or introducing certain elements to food changes it, while older children and teenagers can learn about the chemical components of certain foods and how they interact with each other on the molecular level. No matter how you approach it, the science of cooking is both educational and fun.

There are many different lessons that can be derived from cooking. Every time we prepare food, we are, in effect, performing a science experiment. Foods change when certain elements are introduced into them, be it heat, energy (such as beating or stirring), or other foods. Cooking an egg or popping popcorn are simple demonstrations of how heat changes the properties of food. To demonstrate how energy changes food, place a cupful of shelled peanuts, a pinch of salt, and two or three tablespoons of butter in a Ziploc bag. Use a mallet or rolling pin to crush the peanuts to make peanut butter. Another example is to take a pint of heavy cream and shake vigorously for several minutes until the sloshing sound stops. Open the container and you will discover a lump of fresh butter. To change the way a food tastes, add sugar, salt or lemon juice.

Below is a discussion of several specific types of foods that are ideal examples of cooking science. Much of the information in this article is found at http://www.exploratorium.edu/cooking/candy/index.html. Check them out for a lot more on the subject of science in the kitchen!

The Science of Pickling

Pickling is a method of preserving foods by soaking them in solutions that change the food in a way that make them less vulnerable to spoilage. Pickling is used in all parts of the world with many types of food. Korea has kimchi (a fermented cabbage) and you'll find chutneys in India, miso pickles in Japan, pickled herring (a type of fish) in Scandinavia, corned beef in Ireland, salsas in Central America, and pickled pigs' feet in the southern United States. And that's just the beginning!

There are two basic types of pickles. There are those that are preserved in vinegar, such as kosher dill pickles. The vinegar is a strong acid where few bacteria can survive. Then there are those that are immersed in salt brine, which causes fermentation.

Fermentation actually encourages the growth of "good" bacteria making food resistant to "bad" bacteria, which can cause spoilage. The "good" bacteria eat part of the food and produce new elements that change its texture and flavor. Besides pickles, other examples of foods made by fermentation are bread, yogurt, wine, beer, miso paste and cheese. Fermenting foods requires carefully-controlled conditions, such as temperature and pH, and using special ingredients. For example, the salt brine in pickled vegetables allows the growth of bacteria, which eat the vegetables' sugars and produce tart-tasting lactic acid. In wine, yeast added to crushed grapes produces alcohol. Yeast added to bread dough eats sugars in the flour. The resulting carbon dioxide causes the dough to rise. Cheese is made when bacteria digest the sugar lactose in milk, producing lactic acid, which acts with the added enzyme rennet to curdle the milk. The whey (liquid) is drained off and the curds compacted. Over time, microbes ripen it into a mature cheese.

Recipe for Pickled Cucumber Slices

What you need:
8 large cucumbers, peeled and thinly sliced
C. salt
C. Vinegar
C. Water
2 Tbsp. Sugar
tsp. Paprika
tsp. Garlic Powder
1/8 tsp. Black Pepper
 
What you do:
  1. Place cucumbers slices in large bowl or container. Sprinkle salt evenly over top. Cover and let sit for 30 to 60 minutes to leach out moisture.
  2. Drain out excess water from cucumbers and drain.
  3. In measuring cup combine remaining ingredients.
  4. Pour mixture over cucumbers, tossing to coat evenly. Cover tightly and store in refrigerator for 12 to 24 hours. Makes about 1- quarts of salad.

THE SCIENCE OF CANDY MAKING:

Sugar, or sucrose, is a molecule composed of 12 atoms of carbon, 22 atoms of hydrogen, and 11 atoms of oxygen. Sucrose is actually two simpler sugars stuck together: Fructose and glucose. Dry sugar comes in cube-like shaped crystals. When sugar is added to water, the crystals dissolve, forming a solution. But only so much sugar can be dissolved into a fixed amount of water. However, the higher the temperature, the more sugar can be dissolved into the solution. When cooking candy, sugar, water, and other ingredients are combined under extremely high temperatures. As the solution cools, sugar re-crystalizes, an undesirable effect in many candies such as lollipops, taffy, and caramels. To prevent crystallization, additional elements are added. When fructose or glucose are present, sucrose crystals cannot form. These simple sugars can be introduced in two ways, either by inverting the sucrose (using an acid such as lemon juice or cream of tartar to break sucrose down to glucose and fructose) or by adding a non-sucrose sugar, such as corn syrup (glucose) to the recipe. Hard candies often use a large amount of corn syrup to prevent crystals from forming and ruining the texture. Adding fat, or butter, to a recipe also helps prevent crystallization. Toffee's smooth, creamy texture is due to the presence of butter and the absence of sugar crystals.

Recipe for Hard Candy:

What you need:
1 cup sugar
1/3 cup corn syrup
1/2 cup water
1/4 teaspoon cream of tartar
1/4 to 1 teaspoon flavoring
liquid food coloring
1 to 2 teaspoon(s) citric acid (optional)
a nonstick or enameled saucepan, preferably with a spout
lollipop molds (either metal or white plastic hard-candy molds)
lollipop sticks or wooden skewers cut in half
a candy thermometer
a pastry brush
cooking oil spray
parchment paper
a cookie sheet or marble slab
 
What you do:
  1. Prepare either a marble slab or an upside-down cookie sheet (air underneath the sheet will help the candy to cool faster), by covering it with parchment paper and spraying it with oil. If you're using molds, prepare the molds with lollipop sticks, spray with oil, and place them on a cookie sheet or marble slab.
  2. In your pan, over medium heat, stir together the sugar, corn syrup, water, and cream of tartar with a wooden spoon until the sugar crystals dissolve.
  3. Continue to stir, using a pastry brush dampened with warm water to dissolve any sugar crystals clinging to the sides of the pan, then stop stirring as soon as the syrup starts to boil.
  4. Place the candy thermometer in the pan, being careful not to let it touch the bottom or sides, and let the syrup boil without stirring until the thermometer just reaches 300 F (hard-crack stage). [The hard-crack stage is the highest temperature you are likely to see specified in a candy recipe. At these temperatures, there is almost no water left in the syrup. Drop a little of the molten syrup in cold water and it will form hard, brittle threads that break when bent. CAUTION: To avoid burns, allow the syrup to cool in the cold water for a few moments before touching it!]
  5. Remove the pan from the heat immediately and let the syrup cool to about 275 F before adding flavor, color, and citric acid (adding it sooner causes most of the flavor to cook away).
  6. Working quickly, pour the syrup into the prepared molds and let cool for about 10 minutes. If you're not using molds, pour small (2-inch) circles onto the prepared marble slab or cookie sheet and place a lollipop stick in each one, twisting the stick to be sure it's covered with candy. (It helps to have a friend do this since you need to work quickly.)
  7. Let the lollipops cool for at least 10 minutes, until they are hard. Wrap individually in plastic wrap or cellophane and seal with tape or twist ties. Store in a cool, dry place.

THE SCIENCE OF BREAD:

Everyone loves bread. There are many different kinds of bread throughout the world, both flat and risen. Flat breads are basically flour and water mixed together and baked, with some other ingredients added for flavor. Examples of flat breads include crackers, tortillas, and matzo. Risen breads are those that use leaveners to make the dough rise, giving them their spongy, porous quality.

There are basically two types of leaveners, baking powder or soda and yeast. Baking powder and soda react with other ingredients in the bread dough producing the carbon dioxide necessary to make the bread rise. This method occurs quickly and is used for quick breads (i.e. banana bread), pancakes, or biscuits.

Although adding yeast to a recipe has the same result as adding baking powder, the result is accomplished in a much different way. Yeast is a living, one-celled fungus. There are about 160 kinds of yeasts that live all around us, but the one with which we are most familiar is the one that comes in beige granules used for baking. This yeast is dormant until introduced to moisture. Once the yeast is activated and added to bread dough, it feeds on the sugar present in the flour's starch. Carbon dioxide forms and the bread rises. Unlike baking powder, which reacts quickly, yeast acts very slowly. It also gives bread its distinctive flavor and aroma.

As the yeast works to produce carbon dioxide, the flour in the dough also does its part. Flour contains two proteins, glutenin and gliadin, which, when combined with water, form gluten. Gluten is a gum-like substance that helps trap the air bubbles made by the yeast. Kneading the dough helps the gluten to form. When the bread is baked, the gluten hardens and the yeast dies, leaving behind soft, delicious bread!

Yeast Air Balloon Activity

What you need:
  • 1 packet of active dry yeast
  • 1 cup very warm water (105 F-115 F)
  • 2 tablespoons sugar
  • a large rubber balloon
  • a small (1-pint to 1-liter) empty water bottle
     
    What you do:
    1. Stretch out the balloon by blowing it up repeatedly, and then lay it aside.
    2. Add the packet of yeast and the sugar to the cup of warm water and stir.
    3. Once the yeast and sugar have dissolved, pour the mixture into the bottle. You'll notice the water bubbling as the yeast produces carbon dioxide.
    4. Attach the balloon to the mouth of the bottle, and set both aside.
    5. After several minutes, you'll notice the balloon standing upright. If you don't see anything happen, keep waiting. Eventually, the balloon will inflate. - LWR