Have you ever tried to mix oil and vinegar? No matter how hard you shake or how vigorously you whisk, it doesn't really work. And if you put it on your salad, the oil will stick to the lettuce and the veggies, and you'll have a puddle of balsamic vinegar at the bottom of the bowl.
Here's what's happening:
For the purposes of emulsions, there are three kinds of molecules or substances.
- The first kind are the water-loving kind of molecules. In this category are things like vinegar and lemon juice—basically anything that water would mix into easily. For those of you that remember chemistry, these are generally polar molecules, attracted to the polarity of the water molecule. (Think of polarity kind of like a magnet--it can only stick to other things that can be magnetized.)
- The second kind are the fat-loving kind of molecules, like oil. These are things that don't mix with water. These are generally non-polar molecules, that don't have an interaction with the polar water molecule. The oils, however, generally do like to group with themselves (This is completely inaccurate, but think of these like a bunch of little velcro pieces. It'll help with the next part.)
- The third kind of molecule is one that has properties of both the water-loving and oil-loving molecules. In fact, it's got one end that's polar and one end that's non-polar. Think of it like a magnet with some velcro glued onto it. These are called emulsifiers.
[Cool side note: this is very similar to what soap is made out of--one end velcroes onto the grease on your hands or your pots, and the other end gets pulled away by the magnetic forces of the water.]
When you add an emulsifier to a mixture of oil and water, they magically combine with only mildly vigorous whisking. This is used in things like mayonnaise, in which oil and usually vinegar and/or lemon juice are combined. To make a stable emulsion (one that won't separate over time), you need all three things--water, oil, and emulsifier.
In common food applications, there are three prevalent food emulsifiers:
1. Egg yolk
In processed foods, lecithin (often derived from soy) is added to many products (like chocolate) to help with emulsification.
Next time you make a salad dressing, try this instead, and you'll get a super creamy vinaigrette that doesn't separate on your lettuce.
Creamy Balsamic Vinaigrette
1T balsamic vinegar
2T olive oil
1t Dijon mustard (the yellow stuff doesn't taste right, and it doesn't have enough emulsifiers in it)
1. Dissolve the salt in the balsamic vinegar. (Salt will only dissolve in the water-loving liquids, so you should do this now, before you add the olive oil.)
2. Add the olive oil and the mustard. Whisk to combine. The vinegar and oil should combine together into a homogenous dressing.
3. If there's still uncombined oil and vinegar, add more mustard and whisk. If there's uncombined oil, add vinegar, whisk, and then add more mustard if necessary. If there uncombined vinegar, add oil, whisk, and then add more mustard if necessary.