Soy lecithin is a phospholipid and strong emulsifier derived from soy beans. It is soluble in both fat and water and is used in molecular gastronomy to make incredibly light foam emulsions, which can be served either at room temperature or frozen to make solid foams, which are very airy and ice cream-like. Soy lecithin can be used to make either oil/water emulsions, or air/water emulsions and can convert almost any flavored liquid into a light foam.
The general ratio for using soy lecithin is 1 cup of liquid to 1 gram of soy lecithin. It is generally better to dissolve the soy lecithin into a cold liquid, as heat reduces its emulsifying properties. To obtain maximum foam, the mixture should be worked from top to bottom with a hand blender to incorporate maximum air. If you do not have a hand blender, electric beaters can also work.
There have been conversations about possible health concerns regarding lecithin as a food additive. Today the word lecithin has become a generic word to describe an entire class of phospholipids that are soluble in both fat and water. However, if you ensure the lecithin that you are using has been extracted from soy bean oil in a natural way, it is safe and even has potential health benefits, including helping prevent liver problems.
Additionally, it can help provide maximum flavor flavor with a minimum amount of oil based compounds. For example foaming a salad dressing is a good way to help reduce portion size and help balance the amount of fat in a serving of salad. The incorporated oxygen helps bring out maximum flavor over the unemulsified version of the same liquid.