There's no doubt about it--emulsions are tricky. They're confusing to understand and they're confusing to make. Sometimes even the most seasoned chef can have trouble getting their sauces to emulsify! But if you can start to get a feel for the science behind the scenes, you'll feel more in control and confident next time you decide to whip up a hollandaise sauce for Sunday brunch.
Ready? Here we go!
At its most basic, an emulsion is a suspension two liquids within each other that would not naturally mix.
Think of a liquid--a cup of vinegar, for instance--as made up of millions of tiny droplets. If you pour oil into the vinegar, at first the oil will float on the top of the vinegar because it's less dense. However, if you whisk them together, the tiny droplets forming each liquid start to mix together and become suspended within each other. This is an emulsion.
However, this simple vinaigrette will eventually separate back into vinegar and oil because, at a chemical level, there is nothing holding the drops of each liquid together except for the temporary confusion of having been whisked together.
To get a stable, permanent emulsion, you need to use something to hold the drops of opposing liquid together and prevent them from separating. This "something" is called an emulsifying agent. And this agent is like a mutual friend who holds the oil-based liquid in one hand and the water-based liquid in the other. It creates a chemical bond with each liquid and becomes a bridge between them.
The most common emulsifying agent is an egg yolk, as in mayonnaise and hollandaise sauces. Two others are the casein found in butter and the fine particles of ground dry mustard.
Up next week: why sauces break and how to fix it!
(Photo Credits: Fresh Finds, Emma Christensen, and Kathryn Hill)
Copyright © 2007 Apartment Therapy
the only time this is an issue for me is when i make a vinaigrette. usually, i use mustard or honey (or both!) as an emulsifier for my balsamic and oil. so tasty.
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That bonding agent is also called a "liaison".
Cream is a liaison used in a classic beurre blanc or butter sauce. Butter, an emulsification itself, will separate when heated to a high temperature. By whisking the butter cold into a little bit of hot cream while maintaining a warm temperature the emulsification is maintained.
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The more chemically correct name would be a surfactant. The surfactant does not actually bond with either substance, it is merely a strong attraction. (I am trying very hard to refrain from making some sort of comment about how this relates to people)
The name surfactant is short for surface active agent. The reason it is given this name is because the structure of the molecule attracts it to surfaces, whether it be between 2 liquids, a liquid and your bowl or the liquid and the air. The reason this occurs is because the molecule has 2 sections.
One section is polarized, meaning it contains atoms that do not evenly attract electrons, resulting in small semi-charged sections. Since it has these charged sections, the charged sections are attracted to water, vinegar and other polar liquids. It does not want to be near nonpolar liquids, such as oil because it is uncharged and it leaves an imbalance in the molecule.
One section is nonpolar, meaning it is pretty much just long carbon chains. The carbon chains tend to stay with other nonpolar materials, such as oil. They are repelled by polar molecules so that they can maintain their electrons.
The best way to create a stable emulsion is to start with one liquid, lets say vinegar, and your emulsifier (eggs, mustard, lecithin, whatever your choice). You add a very small amount of the other liquid, your oil, and whisk. Because you are adding such a small amount, these can easily be broken up and dispersed in tiny droplets. When these droplets are formed, your emulsifier forms a ring around the outside of the droplet. The nonpolar side shifts towards the inside of the drop and the polar side shifts toward the outside of the drop. This drop is now stabilized. Now you slowly add more, which will form more drops that will be stabilized by the emulsifier. If your drops get too big then the drops will eventually end up touching. When they touch they join together and form a bigger drop. This bigger drop then touches more drops and eventually your wonderful emulsion separates.
This is the same mechanism as why soap foams and certain additives are in motor oil to help them coat your engine. But that's not so yum.
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