Making Mayonnaise-An Edible Emulsion

Angela D. Patrick                Crown Community Fine Arts Academy
                                 2128 S. St. Louis
                                 Chicago IL 60623
                                 (312) 534-1680

Objectives:

These objectives are for grade levels 2-6.
Students will:
**Conclude that oil and water are immiscible and can not be mixed.
**Discover that an emulsifying agent can be added to two immiscible liquids to 
  stabilize the two liquids to each other when mixed.
**Conclude that the mixture of the three substances is called an emulsion.
**Explain why an emulsion is not a solution.

Materials Needed:

For the teacher:                 Per student group:
large jar with lid               two egg yolks
measuring cups                   1/4 cup vinegar
salad oil                        1/4 cup salad oil
water                            one small clear jar with lid
food coloring (optional)         one small cup or bowl
jar of bought mayonnaise         four small hand lenses
                                 1/4 tsp prepared mustard
                                 1/4 tsp table salt
                                 data sheets

Strategies:

**Number One:
Have students see you measure out two - three cups of water and pour into the 
large jar.  Add about 4 - 6 drops of food coloring to the water and mix 
(optional).  Next measure out two - three cups of salad oil and pour into the 
jar. 

Have the students observe what happens.  Then pick a student volunteer to shake 
up the contents.  Again, have the students observe what happens.  Let the 
contents of the jar sit for 3 - 5 minutes. 

Questions to ask:
What is happening to the oil?
Why do you think that is happening?
Why is the oil in the top layer?

Explanation:
It is impossible for the oil and water to mix together.  They are called 
immiscible- meaning that the two liquids can not be mixed together into a 
solution.  When shaken, the oil droplets become suspended in the water.  
Eventually, the oil droplets enlarge to become a separate layer on top of the 
water.  The oil is on the top layer because it is less dense than the water. 

**Number Two:
Tell students that they are now going to make some mayonnaise, but they must now 
get some oil and water to mix.  Have them to predict what would be needed to 
help the oil and water mix together.  (Optional:  create a prediction chart.)  
Next, have each student count off 1 - 4 to create groups of four. 

Experiment #1
Procedure for students:
1.  Pour the vinegar into your jar.
2.  Pour the salad oil into the jar and put on the lid.
3.  Shake the contents very hard for 3 - 4 minutes, then let it sit 3 - 4 
    minutes.
4.  Compare your jar with your teacher's jar.

Questions for data sheet:
1.  What happened in your jar?
2.  Which liquid remained on top?
3.  How does this compare to your teacher's jar?
4.  What does this mean for the vinegar?

Explanation:
When shaken, the oil and vinegar seemed to mix.  But when the contents were 
allowed to sit, the two liquids formed two separate layers.  The oil remained in 
the top layer.  As a result, this means that the vinegar must be made mostly of  
water. 

Experiment #2
Procedure for students:
1.  Put the egg yolks into the small cup or bowl.
2.  Beat the yolks until they are liquid.
3.  Pour the beaten yolks into the jar with the oil and vinegar and close the 
    lid.
4.  Shake the contents very hard for 3 - 4 minutes.
5.  Observe what happens.

Questions for data sheet:
1.  Describe what happened in the jar.
2.  Why do you think this happened?
3.  Put the hand lens to the jar.  What do you see?

Explanation:
The oil and the vinegar (water) mixed together much better when the eg yolk was 
added.  The lecithin, which is a protein in the egg yolk , acts as an 
emulsifying agent.  Emulsifying agents have regions that associate with the oil 
and regions that associate with the vinegar (water).  Thus the emulsifier (the 
egg yolk), acts as a bridge between both the oil and the water. 

The lecithin molecules in the egg yolk formed a layer around the oil droplets 
and prevented the tiny droplets from coming together to make a separate layer.  
The egg yolk then enabled the oil to mix with the vinegar.  The mayonnaise that 
is being created is an emulsion of oil droplets in water.  This means that it is 
not a solution.  A solution is made when two or more liquids are totally mixed 
together.  Because the oil is still separate from the vinegar even with the egg 
yolk present, it can not be a solution. 

The emulsion created here is a dispersion of one liquid (the oil), inside 
another liquid (the water), with an emulsifier (the egg yolk) acting as a bridge  
to the two liquids for stabilization. 

Experiment #3
Procedure for students:
1.  Add thee mustard and the salt to the mixture.
2.  Again, shake very hard for 3 - 4 minutes.

Questions for data sheet:

1.  Did anything happen to the mixture now?  Explain.
2.  Taste.  Describe the taste.
3.  How does this mayonnaise differ from the one bought from the store?

Performance Assessment:

Teacher will observe the student groups mix the oil and vinegar and the compare 
results with teacher's demo model to conclude that the vinegar is mainly water 
and will not mix with the oil.  By completing the experiments, the student 
groups should determine that the egg yolks added to their oil and water helped 
to stabilize the two liquids. Finally, each student must be able to explain why 
an emulsion is not a solution. 

Group Rubric:
There is one point for each question on the data sheet, and five additional 
points for group participation.  0-5 points = Does not meet; 6-10 points = 
Meets; 11-14 points = Exceeds expectations.