Emulsion: Definition & Examples

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  • 0:00 What is Emulsion?
  • 0:35 Hydrophobic vs. Hydrophilic
  • 1:52 Examples of Emulsions
  • 3:44 Lesson Summary
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Lesson Transcript
Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

Oil and water don't mix! In this lesson learn about emulsions and how they work. Through examples, learn about their abundance in foods and what kinds of foods use an emulsion.

What is Emulsion?

Take a cup of water and a cup of oil, and combine them into a third cup. Instead of the two liquids mixing together, the oil will just float on top of the water. Even if they are mixed together, the oil and water quickly separate again. Next beat up an egg and mix it with the oil and water. Now the oil and water aren't separating. Why is this? How is this possible? An emulsion is a mixture in which the substances combined are not soluble with each other. The substances will not mix or stay mixed with each other without the help of an emulsifier. In the water and oil emulsion, the egg is the emulsifier.

Hydrophobic vs. Hydrophilic

Two important terms to know when it comes to emulsions are hydrophobic and hydrophilic. Hydrophobic means a substance that doesn't mix with or dissolve in water. Hydrophilic is a substance that does mix with or dissolve in water. These terms are easier to remember when you know that hydro means 'water,' -phobic means 'fear of', and -philic means 'love of'. So a hydrophobic material is one that is afraid of water and won't mix with it, while a hydrophilic material loves the water and wants to mix with it as much as possible. In the first example, oil is a hydrophobic substance. Something like sugar is a hydrophilic substance, because if you mix sugar into water it will completely dissolve.

When hydrophobic and hydrophilic materials are mixed, they will quickly separate because they are not able to associate with each other. But sometimes we need these two materials to mix to make a third material. An emulsifier is a material that can help a hydrophobic and a hydrophilic material mix together.

An emulsifier works because it has both hydrophilic and hydrophobic properties. Since it has both hydrophobic and hydrophilic properties, it mixes with both, and by mixing with both, it forces both to mix with each other.

Examples of Emulsions

Many foods are an emulsion. Chocolate milk, cookie dough, butter, many salad dressings, and whipped cream are all made using an emulsion. In cookie dough, sugar and butter are mixed together. Sugar is a hydrophilic substance, while butter is a hydrophobic substance. So how can they get mixed together?

First, vigorous mixing forces them to mix together for a while. The energy put in by mixing forces the individual droplets to break into smaller pieces so that each substance can't just associate with itself. But if left alone this sugar and butter would eventually separate into oil and sugar. That is why the eggs are then added.

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