I think people spend a lot of time trying to get fat out of things. Why would you do that? Fats and oils make food taste good.
Let’s talk chemistry: polar and non-polar molecules. Water is a polar molecule — it’s got one end that’s a little bit low on electrons (a little positively charged) and one end that’s a little bit heavy on electrons (a little negatively charged). Positive and negative attract; water arranges itself so that the positive ends of one molecule are generally pointed toward the negative ends of others. Other polar molecules can fit in to this arrangement very easily — they’ve also got positive and negative ends, so they can disperse among water molecules with no problem.
Oils, though, are non-polar molecules. Well! That’s a second story, folks. They have neither positive nor negative ends, and they don’t play well with water. They tend to huddle together in droplets. There’s less work involved in being in a big droplet than being in a small droplet — so when two little droplets of fat are next to each other, they tend to merge. If I put a few tablespoons of oil and a few tablespoons of water in a clear glass, and whisk them vigorously, I can see this happen — little drops merging into larger drops, until the two liquids have separated entirely.
“Oil and water don’t mix, Sam?” you say, “Wow, what news! I had no idea!” Your sarcasm is noted, dear reader, but stay with me. I promise you’ll learn something.
When I said that fats make things taste good, I didn’t just mean fat tastes good — I meant that fat makes other things taste better. Many flavor-bearing molecules are non-polar, and they don’t mix well with saliva (which is mostly water). Having some fat in the food lets us taste more of the food.
But sometimes the fat in my food tries to escape. Grease floats to the top of my soup, big disgusting drops of butter break free from my sauces, and my vinaigrettes look like fancy layered drinks.
For these problems, and more, I need emulsifiers.
It’s easy to get confused, and think that an emulsifier is something that lets you mix oil and water — a polar and non-polar liquid. The real story is slightly more complicated.
We’re still making a colloid — in this case, a suspension of little droplets of one liquid in another. Emulsifiers are third ingredients we add to keep the droplets suspended. Emulsifiers mostly do two things:
They let us break the little droplets into even smaller droplets (the smaller the droplet, the longer it will take for them to all coalesce).
They resist or even completely prevent the droplets from rejoining.
Soaps and detergents do a great job at letting us break the drops into smaller bits — they’re surfactants, which reduce the surface tension that holds the little droplets together — and so, soap lets me clean greasy things with water. Soap tastes terrible, though.
There are many food-emulsifiers used in commercial kitchens, things like soy lecithin, sodium stearoyl lactylate, and DATEM. If you see these things in ingredient lists on mayonnaise or bread, don’t fear — they’re emulsifiers. In your home kitchen you’ll probably only find a few useful emulsifiers: egg yolk and mustard the two most useful and most common.
Egg yolk is useful for emulsifying sauces; in addition to letting you mix in that pat of butter it will also thicken the sauce, usually a pleasant side-effect. Just remember to temper your yolk by mixing a little of the warm sauce with the cold yolk to bring it to temperature slowly. Otherwise: scrambled egg.
Mustard is useful especially for emulsifying uncooked foods. Vinaigrette are almost always based on an oil, an acid, and a little mustard. The mustard adds some flavor, but mostly it is there to emulsify. Once you know this, it’s fun and easy to invent new dressings: pick an oil, and acid, and add a spot of mustard. Red wine vinegar and sunflower oil. Lemon juice and grape seed oil. Grapefruit juice and sun-dried tomato olive oil. Rice wine vinegar and…
You get the idea.
There is one last type of kitchen-ready emulsion. It’s one I only learned about when fact-checking this article, and it’s called a Pickering emulsion. A Pickering emulsion makes an emulsifier from a mess of particles that don’t dissolve — they collect at the interface between oil and water, and get in the way of the droplets from merging. When I read about it, I had to give it a try to see if I understood. I plopped a few tablespoons of water, a few of canola oil, and maybe a teaspoon of cinnamon into a glass. Why cinnamon? It was available, and I knew for certain that it wouldn’t dissolve — as anyone who has made French toast can attest.
I mixed them vigorously.
And sure enough, after 15 minutes, a little water sat at the bottom, and a little oil sat at the top, but the majority of the glass was filled with odd little cinnamon-colored pearls.
My mind is buzzing with unusual dressings and strange drinks that could be made using Pickering emulsions.
If you understand why your food is made the way it is, it will be easier to remember how to make them again — but more importantly you’ll open doors to an amazing wealth of new, improvised recipes.