In the 1950s, a chemist working for the U.S. Department of Agriculture began conducting research on an interesting new molecule. The chemist was Allene Rosaline Jeanes, and the molecule was dextran, a giant molecule made of thousands of sugar building blocks. Jeanes had great difficulty finding large quantities of dextran until a soft drink company came to her with a bottle filled, not with refreshing root beer, but with something slimy and viscous. Jeanes discovered that the bottle had become contaminated with a bacterium that produced dextran as a byproduct of fermentation. She isolated the bacteria cells and suddenly had a mechanism to produce all of the dextran she needed.
Jeanes also discovered another similar molecule that would become known as xanthan gum. Also produced by a bacterium -- Xanthomonas campestris -- xanthan gum is widely used by the food industry as a thickening agent. It's especially useful in salad dressings to help keep components like oil and vinegar from separating. Xanthan gum is not an emulsifier, however. It works by stabilizing emulsions, increasing the viscosity of the mixture so that the oil and vinegar stay together longer and so that spices stay suspended.
Xanthan gum also creates a smooth, pleasant texture in many foods. For this reason, it appears in ice cream, whipped topping, custard and pie filling. And the really good news: It's not associated with any known adverse effects.
Our final ingredient is not as exotic as xanthan gum, but it rules the roost when it comes to fast food.