Reader Mark asks:
Can you give us some examples of emulsions, and emulsifiers?
Mark, I thought you’d never ask. The most common kitchen emulsions are dairy products. Milk and cream are both emulsions of the fat-in-water type, as are egg yolks. Butter is an emulsion of the water-in-fat type. Other common emulsions are mayonnaise and salad dressings. Hollandaise is a famous one, but there are many others that are lesser known, like chocolate.
As far as emulsifiers go, probably one of the most well known is lecithin. Lecithin is a type of lipid (fat) molecule that’s found in virtually all plants and animals, being a major component in cell membranes. It can be extracted from eggs, but these days we get most of it from soy and sunflower oil. Because lecithin is found throughout the human body, notably in brain tissue, it’s sometimes taken as a dietary supplement. It’s used as an additive in everything from chocolate and baked goods to paint, rubber and gasoline. Lecithin is a rather small molecule with a fat-loving tail and water-loving head.
Casein is a protein that’s the primary emulsifier in milk products. Proteins, as you may recall, are often very long molecules, made up of long chains of amino acids. In the case of casein, some of the links in the chain are fat-loving, and some are water-loving.
Another emulsifier that’s extremely common is mustard, or more accurately, the gum that surrounds the mustard seed. If you’ve ever wondered why mustard is such a common ingredient in vinaigrette dressings, there’s your reason.