Make an Olive Oil Vinaigrette: The Science of Emulsions

Make a prediction

Which jar will stay mixed the longest: plain, with mustard, or with honey? Write your guess on the worksheet before you start. Scientists call this a hypothesis.

What you need

• 3 small jars with lids
• 6 tbsp extra-virgin olive oil
• 3 tbsp red wine vinegar or lemon juice
• 1 tsp Dijon mustard
• 1 tsp honey
• Salt and pepper
• A timer

Steps

1. Put 2 tbsp olive oil and 1 tbsp vinegar in each jar.
2. Jar 1: nothing else. Jar 2: add 1/2 tsp mustard. Jar 3: add 1/2 tsp honey.
3. Close the lids tightly and shake each jar hard for 20 seconds.
4. Set them down and start the timer. Write down when you first see the layers separate in each jar.
5. Taste the best one on a salad!

🔬 Look at a drop of the shaken dressing under a magnifying glass. Can you see the tiny droplets?

⚠️ Safety: Make sure lids are on tight before shaking.

What's happening? The science

Oil and vinegar don't mix because vinegar is mostly water, and oil and water push away from each other. Shaking breaks the oil into tiny droplets that float in the vinegar for a while. This mixture is called an emulsion.

Without help, the droplets join back together and the oil floats to the top because it is less dense. Mustard contains natural emulsifiers that coat the droplets and keep them apart, so the dressing stays mixed much longer.

Think further

• Mayonnaise is an emulsion too. What do you think holds it together? (Hint: egg yolk.)
• Why does the oil float to the top and not sink?

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🖨 Print the worksheet