AP Biology
Lab:  Root Beer: Demonstration of fermentation

History of Root Beer

Our fore fathers made root beer by soaking Sassafras (a type of tree) root in water, and
adding sugar and yeast (yeast for carbonation).  In the early 1900’s however, scientists
discovered that safrole, a chemical found in Sassafras root, was a carcinogen (which means
 it is a cancer causing agent.) Now, a mixture of other herbs and spices makes up “root beer
extract” which is what we now use to make homemade root beer.

   
Background Information

There are two types of respiration: aerobic (requiring oxygen) and anaerobic (without oxygen).
Yeast cells, which are a type of fungus, obtain energy from glucose by a specific anaerobic
process called fermentation.  There are two types of fermentation, lactic acid fermentation
and alcoholic fermentation.  Alcoholic fermentation begins after glucose diffused into the
yeast cell.  The glucose is broken down into 2, three carbon molecules called pyruvate. 
The pyruvate is then converted to carbon dioxide and ethanol.  Don’t get excited, students,
there is very little ethanol in this root beer.  Fermentation is used to make a variety of food
products, including the making of beer, wine, bread, cheese, sauerkraut, and baked goods. 
It is the carbon dioxide produced by the yeasts that give root beer its “fizz.”  This fizz is
produced in store bought root beer by a carbonation machine that forces carbon dioxide
into the root beer mixture, without the aid of our little yeast friends. 

Purpose

To observe fermentation by yeast.

Materials

clean, empty, 2-L plastic bottle and cap                          1 tablespoon measuring spoon                
funnel                                                                                     table sugar
1 cup measuring cup                                                         root beer extract
¼ teaspoon measuring spoon                                 powdered bakers yeast
cold fresh water

Procedure                            

Using a dry funnel, add in sequence

1. Add 1 level cup of table sugar
2. Add ¼ teaspoon powdered baker’s yeast (fresh and active).  You should be able
   to see yeast granules on top of the sugar.  Shake to distribute the yeast grains into
   the sugar.
3. Swirl the sugar/yeast mixture in the bottom to make it concave (to catch the extract)
4. Add with the funnel: 1 tablespoon of root beer extract on top of the dry sugar.  The
   extract sticks to the sugar which will help dissolve the extract in the next steps.
5. Half fill the bottle with fresh cool tap water, rinsing in the extract which sticks to the
   tablespoon and funnel.  Swirl to dissolve the ingredients.
6. Fill the bottle to the neck, leaving about an inch of head space.
7. Securley screw the cap down to seal.  Invert repeatedly to thoroughly dissolve.
8. Label the bottle with the date sealed and the names of group members.
9. Place at room temperature for about three to four days.  Move to a cool place.  If you
   leave it in a warm temperature longer than two weeks, bad things will happen.

Analysis

Answer the * questions the day root beer is made.  All others should be answered when the
root beer is ready.

1. * Describe the appearance of the root beer during the bottling process.
2. Describe the appearance of the root beer after fermentation.  How is it different
   from #1?
3. *Why were the yeasts necessary in this experiment?
4. *Why was sugar necessary?
5. Explain how the root beer came to be carbonated.
6. *Explain how commercial (store bought) root beer is carbonated.
7. *List the ingredients to make root beer.
8. Why did we put the yeasts in the warm water for five minutes?
9. *Describe the process of fermentation.