Root Beer Lab
A Demonstration of Fermentation!
History of Root Beer
Root beer was made by our forefathers by soaking Sassafras (a type of tree) root in water, and
adding sugar and yeast. In the early 1900s, 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 (a type of fungus) obtain energy from glucose (sugar) by a specific anaerobic process
called fermentation. There are two types of fermentation: lactic acid fermentation and alcoholic
fermentation. Both of these processes have been used to make different foods and drinks all over
the globe.
Alcoholic fermentation begins after glucose diffuses into the yeast cell. The glucose is broken down
to yield a small amount of energy (ATP) for the yeast cell. In addition, two 3-carbon molecules
called pyruvate are made. The yeast cell then converts pyruvate into CO2 and ethanol. Don’t get
too excited… the amount of ethanol produced in our lab is very tiny!
Fermentation is used to make a variety of food products, including beer, wine, bread, cheese,
sauerkraut, and baked goods. It is the carbon dioxide produced by the yeast cells that give root beer
its “fizz”. This fizz is produced artificially in store bought root beer, without the aid of our little
yeast cell friends.
The equation for anaerobic alcohol fermentation is:
C6H12O6 (glucose) → 2C3H4O3 (pyruvate) + 4H+→ 2CO2 + 2CH3CH2OH (ethanol)
(ethanol) (ethanol)
For the first two days, the yeast will use aerobic respiration to grow and reproduce. Eventually,
because the oxygen supply gets depleted, the yeast cells will shift to anaerobic respiration to obtain
its energy. This will supply the root beer with carbon dioxide (the “fizz”) and give it a unique flavor
due to the small amount of ethanol produced.
Procedure *This procedure will produce 2 bottles with 473 ml in each.
1)
Clean and sanitize two 20-ounce screw-cap bottles with warm soap and water, then a
mild bleach solution. Rinse well.
2)
Label bottles with name, date, and class period.
3)
Using a graduated cylinder, measure 473 ml of tap water. Pour into one of the bottles.
Mark a line on the bottle at the water level. Pour out water and cap bottle to keep clean.
Repeat with second bottle.
4)
In a disposable cup, mix 1/16th tsp. of yeast (half of 1/8th tsp.) with 1 cup of pre-boiled
water cooled to 85-95° F. Let yeast sit for 10 minutes; make sure it is fully dissolved
before continuing!
5)
In a clean 1-Liter beaker, mix ½ cup sugar, ¾ tsp. root beer extract, and 800 ml warm
tap water. Stir with spoon until sugar is dissolved.
6)
Add dissolved yeast solution to sugar solution. Mix well.
7)
Pour mixture into each bottle (up to the mark you made earlier).
8)
Record initial observations in your lab notebook. Describe the color, smell, taste (use a
cup to drink a small sample to keep the bottle sanitary). Also, be sure to write any
changes to your procedure that you did during the lab.
9)
Cap your bottle and parafilm the cap. Place the bottle on the side to check for leaks.
Incubate the bottles at room temperature for 3-4 days. Then place in refrigerator for
another 2-3 days.
Results
Before opening your bottle, write down your observations of the bottle. Describe the sound made
when opening your bottle. Describe your root beer in terms of carbonation, odor, sweetness,
yeastiness and overall flavor. Try to quantify these characteristics on a rating scale from 1 – 5 (5 is
high). Compare your bottle to a commercial brand of root beer using the same rating scale.
Conclusion
Explain the results of the root beer in terms of the fermentation process. Include the purpose of
the yeast, the purpose of the sugar, where the carbonation came from, and summarize the aerobic
and anaerobic respiration that took place.