The World of Yeast!

Biotechnology has been around for thousands of years. As long ago as 4000 BC, the Egyptians began using a living organism to make their food better. Yeast is a living organism used in bread to make it rise. It consists of single-celled fungi that reproduce mainly by budding (a small bump forms on the surface of the yeast cell and grows until it forms a wall and separates from the original cell). Given the right conditions (yeast needs sugar, water, air and warmth), even yeast that is sold as a powder will grow and multiply! Try this experiment in your classroom to demonstrate that yeast needs food to grow and has special food needs just like humans. In this experiment, you will be able to tell how much the yeast is growing because of one of the properties of yeast - yeast expels carbon dioxide as it grows. You will provide the yeast with four different food sources: syrup (partially processed sugar), flour (high in starch), gelatin (high in protein) and grape juice (natural sugar). By comparing the relative sizes of the balloons at the end of the experiment, you will be able to tell which food is the best for yeast.

You will need:

• 360 ml of warm water
• Three packets of powdered yeast
• 120 ml of corn syrup
• 120 ml of flour
• Unflavored gelatin (needed to make 120 ml of gelatin solution)
• 120 ml of unsweetened grape juice
• Large measuring cup
• Mixing bowl, jar or other medium-sized container
• Tablespoons
• Four clean glass pop bottles (750 ml each)
• Four large balloons
• Masking tape
• Pen
• About two feet of string (to secure the balloons on the mouths of the pop bottles)
• Large towel (to prop up the mouths of the bottles)

1. In the mixing bowl or jar, mix 240 ml of warm water and the yeast.
2. Prepare the gelatin according to the directions on the package.
3. In the measuring cup, mix 120 ml of corn syrup and four tablespoons of the yeast solution. Pour this into one of the glass pop bottles, and label it with masking tape.
4. Wash the measuring cup. Mix 120 ml of flour with the remaining 120 ml of warm water and four tablespoons of the yeast solution. Pour this into another pop bottle and label it with masking tape.
5. Wash the measuring cup again. Mix 120 ml of the gelatin solution and four tablespoons of yeast solution. Pour this into another bottle and label it with masking tape.
6. Wash the measuring cup. Mix 120 ml of grape juice and four tablespoons of the yeast solution. Pour this into the last pop bottle and label it with masking tape.
7. Make the four balloons stretchy by blowing them up and then releasing the air. Carefully place a balloon over the mouth of each pop bottle. Wind some string around each of the bottlenecks to avoid air going in and out of the bottles.
8. Place all of the bottles in a warm place on their sides, with a towel rolled up underneath the neck so the liquid does not flow into the balloons. Check the bottles every half-hour. Each time you check, shake the bottles gently to mix the liquid inside. Allow the experiment to run for at least two hours.