STEM Activity: Salad With a Side of Science

Have you ever encountered a drink or dressing that seems to separate into layers? It’s not that the ingredients don’t get along – just like oil and water, some liquids have different densities and polarities keeping them apart. Emulsification is the process of combining two or more of these liquids that normally do not mix. See STEM in action as you build a simple salad and create your own emulsified dressing with this recipe!

Materials Needed

For the salad:

• Cucumber, chopped*
• Large bowl
• Lettuce or other leafy greens, chopped*
• Red onion, chopped*
• Salad tongs or forks

*Ask an adult to assist with chopping the salad ingredients. Always have adult supervision when handling sharp objects.

For the dressing:

• Clean jar with a lid, 8-10 ounces
• Dijon mustard, 1 teaspoon
• Extra virgin olive oil, 1/3 cup
• Honey, 1 teaspoon
• Lemon juice, 1/4 cup
• Measuring cup and spoons
• Salt and pepper to taste
• Small garlic glove, minced or grated (optional)

Step-by-Step Instructions

1. Build your salad:
   • Add the chopped lettuce, cucumber and red onion to a large bowl.
      
   • Consider adding more ingredients, like tomatoes, carrots or cheese – get creative for your ideal mix!
      
2. Create your dressing. Add to your jar:
   • 1 teaspoon of Dijon mustard
      
   • 1 teaspoon of honey
      
   • 1/4 cup of lemon juice
      
   • Salt and pepper to taste
      
   • Small garlic glove, minced or grated (optional)
      
3. Place the lid on the jar and check that it is sealed.
    
4. Shake the jar to mix the ingredients.
    
5. After the ingredients are mixed, remove the lid and pour 1/3 cup of extra virgin olive oil into the jar.
    
6. Replace the lid on the jar and check that it is sealed.
    
7. Without shaking it, slowly turn the jar upside down and observe the oil.
   
   What happens? How does the oil and lemon juice mixture interact in the jar?
    
8. Emulsify your dressing! Shake the jar vigorously for several seconds.
   
   What changes occur after shaking the jar?
    
9. Open the jar and taste your dressing with a clean spoon.
   
   If it’s too lemony, add a few more tablespoons of olive oil. If it’s too oily, add a few more tablespoons of lemon juice or Dijon mustard.
    
10. Drizzle your emulsified dressing over the salad. Then, gently toss with salad tongs or two forks to distribute the dressing.
     
11. Store any leftover dressing in the fridge for up to one week.
    
    If the dressing settles and the oil separates again, just shake to combine.
     
12. Serve your salad to family or friends and share your scientific discoveries!

What Are We Discovering?

When you added the oil, you probably noticed that it settled on top of the lemon juice mixture. Then, after shaking the jar, tiny droplets of oil were dispersed in the lemon juice mixture, creating an emulsion!

However, lemon juice is mostly water, and an emulsion of oil and water separates quickly without an emulsifier, a substance to stabilize an emulsion. That’s where the Dijon mustard comes in handy! Compounds in the mustard coat the oil droplets, keeping your salad dressing smooth. Without it, you would have globs of oil and juice – yuck!

Many industries, from cosmetics to pharmaceuticals to environmental remediation, use emulsification! NASA engineer and National Inventors Hall of Fame^® Inductee Jacqueline Quinn designed a new way to clean up pollution created by early space explorations. Her invention, EZVI (Emulsified Zero-Valent Iron), absorbs pollutants from the soil, neutralizes them and converts the pollution into harmless substances. The system acts like a sponge, pulling the contaminant into the emulsion!

Learn More

Hungry for more hands-on kitchen experiments? Check out this activity to keep exploring STEM in the kitchen! Then, sign up to receive monthly emails filled with inspired approaches to everyday STEM.