Everything Kids' Magical Science Experiments Book (4 page)

There is another theory about ice melting under pressure that claims it's not pressure that causes the ice to melt. Instead, this theory claims that certain materials conduct heat better than others. These materials include copper wire. As a result, it is the heat passing through the wire that causes the ice to melt, not the pressure. What does this experiment indicate to you about the truth of this theory?

To extend this experiment, try varying the weights that hang from the ice and measuring the time necessary for the wire to pass completely through the ice. Is there a weight that will not cause the wire to pass through the ice?

For centuries, bakers have sought that perfect recipe, the perfect combination of ingredients, cooking time, and chemistry to produce mouth-watering delights for all to enjoy. Sometimes, simply walking into a bakery is enough to make your stomach growl with anticipation, as the smells overwhelm you: cookies, cakes, pies, and perhaps the most comforting smell of all, the smell of freshly baked bread.

What bakers know that many of us who aren't as talented in the kitchen do not is that a perfect loaf of bread doesn't happen by accident. It often requires planning, careful measuring, patience, and one special ingredient: yeast.

Question: Do yeast cells like it hot or cold?

In this experiment, you will get to act like a real baker and make a small amount of bread dough. However, in order to test the effect of temperature on the growth rate of the yeast, you will be using water of varying temperatures and measuring the growth for each temperature. You should not attempt to eat any of the dough balls you produce—they are merely for experimentation. At the end of this experiment, you will get a recipe for making a real loaf of bread. With an adult's help, you can bring your project to a tasty conclusion!

Yeast typically is found in its dry form, often in a jar that can be purchased at the grocery store. This prepared form of yeast needs to be mixed with water in order to “come to life.” The water allows the yeast cells to begin growing, and you usually will see this happen as the water appears to foam when yeast is mixed in. Next, the foaming water is usually mixed with a small amount of flour and then the rest of the bread dough is mixed together.

Which is the faster hot or cold?

You don't need to use magic to learn the answer to this silly science question — all you have to do is think of the number suggested by each clue. Then, circle the word in the column with that number. For example, you have one nose. So, for the first clue, “nose,” circle the word in column 1 (for 1 nose). When you are done, read the circled words from bottom to top.

Yeast, like most living creatures, grows best under the right combination of water and warmth. When the yeast starts to mix with the flour, the starch in the flour becomes the diet for the hungry yeast cells. As they feed, they give off carbon dioxide (similar to the bubbles you would find in a can of soda) and alcohol. The flour then captures this gas, and forms tiny pockets of air. As these air pockets increase and grow, the dough rises and fills out into its final shape for baking.

You might be wondering whether anything can speed up or slow down the process by which yeast reacts to make bread rise. The answer is yes. Salt actually slows down the reaction, while sugar speeds it up. Often, bakers will use combinations of salt and sugar to regulate the rate of rising of their breads or rolls. But even more than the ingredients used, temperature probably has the largest effect on the rate at which bread dough rises. Using water that is too hot or too cold can significantly reduce the effect of the yeast. In addition, the outside temperature during the rising can also greatly affect your results. This experiment will give you several different ways to measure the effects of these factors on the rising of bread dough that has been leavened by yeast.

Note:
This set of ingredients will produce a single ball of bread dough. As you create different test doughs, you will simply modify one or more of these quantities.

• 100 grams (3.5 ounces) white flour
  
• Dash of salt
  
• 1 teaspoon white sugar
  
• ¼ envelope dry yeast (about ½ teaspoon)
  
• 50 mL (1.69 ounces) water
  
• Measuring spoons
  
• Glass measuring cup (one that measures up to 2 cups)
  
• Mixing bowl
  
• Bowl for holding the completed dough
  
• Kitchen or paper towel
  
• Ruler or other measuring device
  
• Teaspoon (for stirring)
  
• Candy/Deep frying thermometer
  
• Notebook for recording data
  

1. Select at least four temperatures for the water you will use in this experiment. Some options are:• Water that has been sitting at room temperature for at least 30 minutes• Water taken directly from the refrigerator• Water that has been placed in the freezer, but has not yet frozen• Water that has been heated in the microwave for one minute• Water from an “Instant Hot” faucet• Water that has been left outside on a warm day
   
2. Measure the temperature of your water and record it in your notebook.
   
3. Pour 50 mL of your chosen water into the measuring cup and slowly mix in the dry yeast until it dissolves or begins to foam.
   
4. In the mixing bowl, pour half of the flour and mix in the yeast mixture until a wet dough forms.
   
5. Add the salt, sugar, and the remaining flour and mix thoroughly until a smooth dough forms.
   
6. Remove the dough from the mixing bowl and form into a ball with your hands. Carefully measure the diameter of your dough ball and record it in your data notebook.
   
7. Place the dough ball in bowl, cover with a towel and set on the counter.
   
8. Repeat steps 2–7 with each of the different temperatures of water you have chosen to test in this experiment. When you have completed this stage, you should have several bowls of rising dough.
   
9. Let the dough balls sit out for at least four hours (overnight works best) and then carefully measure the diameter of each dough ball to see which one grew the largest.
   

1. What temperature was the most effective for causing your bread to rise? Why do you think this temperature worked best?
   

   

2. Could you detect any smells coming from your bread? What did it smell like? What do you suppose caused those smells?
   

   

3. What might have happened if you had let the dough sit for a longer period of time, several days for example?
   

   

4. Research ideal water temperature for rising bread dough to see how closely your results agreed with that recommended temperature.