Emulsified sauces are one part chemistry, one part culinary magic. Take two ingredients which, “like oil and water”, should not blend together, and with a little effort, they become one delicious whole.
An emulsified sauce is literally the blending of fat (butter or oil) and water (wine, vinegar or egg yolk- which is more than 50% water). Combine them together with heat, centrifugal force, or just a vigorous whisk and you suddenly have one sauce where there were once two separate ingredients which typically do not play well together.
The scientific term for this refusal to mix is “immiscible” which is defined as two liquids that are incapable of being mixed, caused by surface tension between two molecules. However, when it comes to emulsified sauces, there are other forces at play (heat and/or movement) which will cause one part to incorporate into the other.
The best known emulsified …