The Science of Bread: Feeding the Yeast

Getting ready to feed some yeast and observe cellular respiration

Today we got to do a really neat experiment showing the process of cellular respiration.  The students mixed sugar and yeast in a flask with warm water and covered with a balloon.  Cellular respiration uses oxygen and glucose taken into the mitochondria and converts it into energy, water and carbon dioxide.  

The carbon dioxide gas, a product of cellular respiration
is causing the balloon to expand

The yeast, even though they don't look alive, are actually simple unicellular organisms! In the picture above we can see the finished product.  Look at all of that carbon dioxide gas developing.  

Go ahead and try this at home (with supervision of course)!

here are a list of materials:

1 cup of warm water

2 tablespoons of dry active yeast

3 sugar cubes or 2 tablespoons of sugar

1 balloon

1 flask (you can use a small water bottle)

You can even take your yeast mixture and make bread out of it.  

• 3/4 cup warm water
• 1 package active dry yeast
• 1 tsp salt
• 1-1/2 tbsp sugar
• 1 tbsp vegetable shortening
• 1/2 cup milk
• 3 cups all-purpose flour, approximately

Just combine flour salt milk and shortening with your yeast mixture until it becomes a dough.  Here is the rest of the recipe from about.com.  

1. Turn dough out onto floured board and knead, adding small spoonfuls of flour as needed, until the dough is soft and smooth, not sticky to the touch.
   
2. Put dough in buttered bowl, turn dough over so that the top of dough is greased. Cover and let rise in warm spot for 1 hour.
   
3. Punch down dough. Turn out onto floured board and knead.
   
4. Preheat oven at 375 degrees F.
   
5. Form dough into loaf and set in buttered bread pan. Cover and let rise for about 30 minutes.
   
6. Score dough by cutting three slashes across the top with a sharp knife. Put in oven and bake for about 45 minutes or until golden brown.