Delicious Smelling Chemistry

As humans, we use our sense of smell for many different purposes. Smells inform us if food has rotted, if there is a fire nearby, or if there are potentially dangerous gases or chemicals around. The olfactory system is a complex set of processes that include membrane receptors in the nose, electrical signals, and our brain. However, humans would not be able to detect smells unless the appropriate odor molecules are released into the air.

In this activity, students will use household materials to investigate and explore their ability to smell an odor. Students will compare and contrast results to determine if some individuals have a better sense of smell than others. Students also will observe the Maillard reaction and how different odor molecules are released into the air.

Activity Materials
Plastic cups – 8 for each student, plus one for each group of students
Measuring cups and spoons
Vinegar
Coffee beans – enough for a plastic cup-full for each group of students
Pitcher of water
Non-stick skillet
Corn syrup
Amino acid tablets – available at health food stores
Permanent markers – one for each group of students
Oven mitts or gloves
Stove or hot plate
*Data table (optional)

Vocabulary
Olfaction: the sense of smell
Maillard (pronounced meh-YAR) reaction: a chemical reaction between amino acids and sugars created by heat. It is named for the French chemist Louis-Camille Maillard, who first described it around 1910.
Amino acids: compounds that form the basic structural units for all proteins.
Volatile: a substance prone to evaporation at relatively low temperature.

What To Do

1. Begin the lesson by having students watch the Science Friday video “Suckers for Sap.” Begin a discussion with the students about how humans use smell to help in food preparation.  How do we use smell to determine when a meal is ready to eat?

2. Tell students that they will conduct an experiment to investigate how well they can smell and where smells come from.

Experiment 1

1. Hand out eight cups to each student and have them label each with a number from 1 to 8 with a permanent marker. Place a small cup of coffee beans on each table for students to share. Tell students that they will need to sniff the coffee beans in between each smell test. Ask students what they think will happen if they do not.

2. Have each student create a T-chart to compare their observations of smells for two different cups numbered #1 and #2.

3. Have students fill cup #1 with one cup of vinegar, and cup #2 with ½ cup of vinegar and ½ cup of water. The vinegar-water solution is half concentrated, compared to the cup of pure vinegar. Ask students how they think this will affect the smell from each cup.

4. Have students smell each cup from the same distance and record on their chart whether the scent of vinegar is strong, not very strong, or if there is no smell at all.

5. Have students continue the experiment by following the measurements listed in their chart for each cup, and recording their observations on the degree of smell. Remind students to sniff the cup of coffee beans before each smell test in order to cleanse their nasal passages from previous smells. What do they predict will happen as the vinegar is diluted? Do they think that they will be able to smell the vinegar even in the smallest concentration?

6. Have students compare and contrast their smell charts. How were the results different or the same? Were some students able to smell even the smallest concentration of vinegar?

Experiment 2
Note: Since this experiment requires the use of a hot stove and skillet, we recommend that an adult conducts it as a demonstration, or that the appropriate safety materials are used and safety guidelines are discussed prior to the experiment.

1. Place one teaspoon of corn syrup in a skillet, and place the skillet on a stove or hot plate. Turn the heat on low.

2. Open one of the amino acid caps and allow students to smell the powder inside the cap. Does it have a strong aroma?

3. Sprinkle the powder onto the corn syrup in the skillet and turn the heat up. What do students think will happen? What reactions do they think will occur?

4. Move the skillet back and forth to mix in the powder with the syrup. What do students smell? Do the odors change as the mixture continues to heat up on the skillet?

What’s Happening?
Smell involves the detection of volatile molecules as they float through the air and into the receptors in your nose. This means that the smell of baked chocolate chip cookies comes from a combination of odor molecules from the ingredients that have evaporated into the air. These odor molecules float into your nose and adhere to a receptor that allows your brain to perceive the smell.

The first experiment demonstrates that as the vinegar is diluted, there are fewer vinegar odor molecules exposed to our noses. The experiment also may demonstrate that some individuals have a heightened sense of smell, and may be able to smell even the smallest trace of vinegar. A person’s ability to smell can vary, depending on genetic factors or current health conditions.

The second experiment demonstrates the Maillard reaction, in which new compounds are created by the chemical reaction between the amino acid powder and glucose in the corn syrup. These new compounds create a variety of odor molecules. Besides creating new aromas, the Maillard reaction also creates new flavors, and is very important in the preparation and presentation of many foods and in food science, like maple syrup!

Topics for Science Class Discussion
• How does the loss of your sense of smell affect your other senses?
• Why do certain smells stir up memories?
• Why do we stop smelling an odor that we have been exposed to for a long period of time?
• Why does the scent of coffee beans clear your sense of smell?
• How do animals (ants, wolves, skunks, etc.) use their sense of smell to communicate or defend themselves?

Suckers for Sap

For centuries, maple syrup producers across New England and Canada harvested sap by drilling into the bark of fully grown wild trees. While commercial syrup producers have adopted vacuum pumps and plastic tubing to aid these efforts, recent experiments at the University of Vermont’s Proctor Maple Research Center may further pull the industry from its pastoral roots. In the Science Friday Video “Suckers for Sap” you’ll learn about an important chemical reaction used to convert the collected sap into delicious maple syrup.

• Extend this experiment by having students try to place the cups in sequential order, from most pungent to least pungent, by sniffing them. Hide the right sequence under the cup to prevent students from seeing the correct order.
• Explore how smells diffuse through the air. Spray some perfume in the corner of a room and have students stand at different locations around the room. Have them raise their hands as soon as they smell the perfume. How long did it take for the perfume molecules to reach each side of the room? What could make the diffusion faster or slower?
• Explore the relationship between our sense of smell and taste. Have students pinch their noses closed while tasting various fruit-flavored candies. Can students identify the flavor without their sense of smell? Have students release their noses while chewing the candy. Was there an immediate difference in the taste? Why?
• Have students research the olfactory system of various types of animals and compare to a human’s sense of smell. Which animal has the strongest sense of smell? Why do these animals need a heightened sense of smell?
• Explore sense of smell through a variety of activities from the Franklin Institute:
  http://sln.fi.edu/qa97/me11/me11.html
• Read how astronauts use an electronic nose in space:
  http://spaceplace.jpl.nasa.gov/en/kids/enose_do1.shtml
• Learn more about the parts of your nose and how the human olfactory system works:
  http://kidshealth.org/kid/htbw/nose.html

National Standards: NS.5-8.1, NS.5-8.2

This lesson plan was created by the New York Hall of Science in collaboration with Science Friday as part of Teachers Talking Science, an online resource for teachers, homeschoolers, and parents to produce free materials based on very popular SciFri Videos to help in the classroom or around the kitchen table.

The New York Hall of Science is a science museum located in the New York City borough of Queens. NYSCI is New York City’s only hands-on science and technology center, with more than 400 hands-on exhibits explore biology, chemistry, and physics.