So asks reader Wale, and it’s just the sort of question I like to answer on a Wednesday morning. The short answer is that an emulsifier is a substance that keeps an emulsion stable. But then what exactly is an emulsion again?
Emulsions are combinations of liquids that don’t normally like to be combined. In the kitchen those liquids are usually oil (or melted fat) and water. Like the members of Arcade Fire and the Flaming Lips, they don’t like to mix with each other very much, yet they can be made to with effort. Shake a jar containing water and olive oil vigorously and you’ll get an emulsion: millions of tiny oil droplets inside the water phase. The problem is that it won’t last very long. After about a minute or so the oil droplets start to recombine and the two phases separate again.
What to do? Well it turns out that certain other compounds that can be added to an emulsion to keep it from breaking — to stabilize it, in other words. Lots of different types of molecules can be used as emulsifiers in an oil-and-water emulsion, but what they all have in common is that one end of them is water-loving (hydrophilic) and the other is fat-loving (lipophilic). When added to the emulsion, the fat-loving ends bury themselves in the oil droplets with their water-loving ends sticking out. The result is a coating around the oil droplet that repels other oil droplets, keeping them from combining with each other.
Neato, yes? Common kitchen emulsifiers include egg yolks and soy (which contain lecithin), mustard (which contains emulsifying seed gums) and honey (which contains, er…I’m not sure). Commercial ingredients companies produce bewildering varieties of emulsifiers, usually mono-and di-glycerides which unlike tri-glycerides have water-loving regions on them. But there are all sorts of others.
Most people only think about emulsifiers in applications like salad dressings, mayonnaise and hollandaise. In fact emulsifiers are critical in the baking world as well. Egg yolk lecithin turns a chewy open crumb like this into a tender tight crumb like this. In other words, they’re essential for creating texture. But they also play a preservative role as well, as large blobs of oil or fat oxidize (spoil) more quickly than lots of tiny, well-dispersed ones. Oh yes, the benefits of emulsifiers are legion. Best not to get me started, I could go on about food additives all day, and I have work to do.