Lecithin is a naturally occurring molecule found in egg yolks, soybeans, liver and wheat germ. It is also a constituent of cell membranes throughout the human body and is found in large quantities within our stomachs, blood and brains.
Lecithin is a natural emulsifier and helps to allow fat to remain soluble in high water compounds. Mayonnaise, salad dressing, ice cream and sorbet are just some of the common emulsions that lecithin can help to facilitate. Many butter based sauces are also emulsions, like beurre blanc, hollandaise and béarnaise. Lecithin is also used in the creation of stable foams in molecular gastronomy.