The Science of Food: Emulsions on your Salad!


April 29, 2009
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Emulsion Repulsion: Science on your Salad!

A simple way to explain an emulsion is as a suspension of two liquids within each other that normally would not mix (like oil and water).  Picture a cup with vinegar.  If you pour oil into the vinegar, the oil will float on top of the vinegar because it is less dense.  What happens if you briskly whisk them together?  Well, the liquids start to mix together and tiny droplets of each liquid become suspended within each other.  When they are uniformly dispersed in each other (evenly mixed) then you have an emulsion.

A simple mixture of oil and vinegar will ultimately separate back into vinegar and oil because at a molecular level, there is nothing holding the two kinds of liquids together. This temporary emulsion just happens because of the whisking. To get a permanent emulsion of these two liquids you need a third ingredient to hold the two immiscible (non-mixing) agents together and prevent them from separating.  This ingredient is called an emulsifying agent.  This agent is like a mutual friend who likes both the oil and the vinegar and holds them together.  It creates a weak chemical bond with each liquid and becomes like a bridge between them.  Eggs are a very common emulsifying agent as is mayonnaise and hollandaise sauce.

Now that you understand emulsions, go into your kitchen and make your own!

egg-whisk-2
 Creative Commons License photo credit: LDCross

Materials:
Measuring cup
Measuring spoons
Vegetable oil
Vinegar
2 Mixing bowls
Whisk or hand egg beater
1 Egg

Procedure:

Part 1
1. First grab an adult to help you.  Also, we will be using a raw egg, so this experiment is not for eating, it’s just for experimenting!
2. In a mixing bowl, place ½ cup of vegetable oil.
3. Add one teaspoon of vinegar and use a spoon to gently mix them together.  Observe what happens.
4. Now, use the whisk or a hand eggbeater to mix the vinegar and oil.  What happens now? 
5. Watch the mixture for a few more minutes.  Observe what happens.  They should begin to separate.  Oil and vinegar do not stay well mixed.

Part 2
1. In a separate bowl, add one teaspoon of vinegar and an egg yolk (you will need to separate it from the egg white first).  Mix these two ingredients together well.
2. Now, add one cup of oil and two teaspoons of vinegar.  Mix the egg mixture together using the whisk or eggbeater.  What happens?  Observe.
3. Discuss your results. 

Emulsions aren’t just an experiment, though – they’re something you can see everyday. In honor of Big Bite Nite tomorrow night, Chef Sandor Edmonson from *17 at the Alden and I whip up a tasty vinaigrette. Click the video below to see the dish in progress as we create great example of an emulsion.

Want to learn how to make more food at home?
Learn the ingredients for ice cream.
Learn how to make your own butter.

Want to see more in the Science of Food video series?
Watch me make ice cream with Quattro’s Executive Pastry Chef Philippe Valladares.
See me make butterwith Adam Puskorius, Executive Chef at Polo’s Signature.


Kat
Authored By Kat Havens

Kat has been both the spokesperson for the CSI: The Experience exhibit and project manager for the Imperial Rome exhibit and has a love of all things historical and cultural. She is responsible for the Xplorations summer camp program, coordinating weekday labs during the school year, writing department curriculum and presenting at teacher trainings. Kat has worked at the Museum since 1996.

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