Cooks and food preparers have been working with emulsions -- two or more liquids that can't normally be mixed together -- for a long time. Fortunately for our taste buds, they've discovered several substances that encourage liquids to overcome their unwillingness to combine. These substances are known as emulsifiers.
Egg is commonly used as an emulsifier, but most food manufacturers today use glycerides obtained from palm oil, soybean oil, sunflower oil or tallow. Vegetable oils and animal fat contain mostly triglycerides, but enzymes can be used to break down triglycerides into mono- and diglycerides. These are the ingredients you see so frequently on fast-food menus.
Mono- and diglycerides allow smooth mixing of ingredients, prevent separation and generally stabilize food. You can find them in ice cream, margarine, baked goods, whipped topping and certain beverages. Luckily, glycerides pose no serious health threats, although they are a source of fat. The U.S. Food and Drug Administration has classified them as a "generally recognized as safe" substance, indicating that experts consider them safe as food additives.
Next up, we have one of the most versatile ingredients in all of fast food.