You know oil and water don’t mix, but do you know why? First off, oil and water have very different densities. Water molecules are packed together more densely than oil, so when you add two of them to a container they will naturally separate. Anyone who has made a vinaigrette has seen this separation in action. Secondly, water molecules arepolar, meaning that they have a positive and negative end. Since we all know that positives and negatives attract, this means that water, in general, likes to stick together. Oil molecules, on the other hand, are nonpolar, so water molecules don’t have much interest in bonding with them. Think of it like a sixth grade dance. You’ve got a tight-knit group of girls and a gang of disinterested boys and nobody seems to be dancing. But many recipes, from basic vinaigrettes to creamy pan sauces, require that you, essentially, get those kids paired up. How do you defy the laws of science? By creating an emulsion. https://youtu.be/arwG_MFbTz4 An emulsion is simply the combination of two substances that don’t usually mix. To create an emulsion between oil and water, you can vigorously blend, whisk or shake the two together to break the oil molecules into smaller bits that can be suspended in water. Keep in mind, though, this is only a temporary emulsion, and the two will eventually separate again. To make the emulsion last, you need an emulsifier.