What Is An Emulsion?

You've seen people emulsify things on cooking shows, and maybe seen "emulsion" on a fancy menu, but you might still be thinking, "What is that, exactly?" Time to strap on your learning boots — we're going the educational route. What is emulsification?Emulsification is a scientific process in which two immiscible (unmixable) liquids are mixed together in a way that makes them stay mixed. You probably know that oil and water don't mix, but that mayonnaise on your sandwich? That's an emulsion. It's oil and vinegar, like salad dressing. The egg yolks help bind the two sides that would normally not want to come together; combining them by force forms something with a texture that's completely different from its individual parts.

How does it work?Emulsifying something means you're either dispersing fat into water (mayonnaise, pan sauce) or water into fat (vinaigrette, butter) to make something with a uniform look and feel. In the case of the vinaigrette on your salad, you're dispersing oil into water (vinegar is the water element here). Sometimes you can see the oil floating on top of the vinegar, and sometimes they're mixed together. They're both delicious, but only the second one has been emulsified. Sauces and dressings that have a uniform consistency taste better, look better, and have a more pleasant mouthfeel. It also helps your sauce or dressing coat your food. Having dressing stick to your salad and sauce stick to your pasta is the goal.How can you use emulsification?You may have noticed above when I mentioned butter that dairy products are natural emulsions of dairy solids (fats) and water, which is pretty cool. They change as you add more fat. Heavy cream has more fat than milk, so it's more viscous, or "creamier." Butter has more fat than both of those, and is arguably "the creamiest." See where I'm going with this? Sadly, nature does not provide us with all the emulsions we need. Sometimes we need a little science to make it so. If you have access to a fancy lab, you can probably find something that vibrates rapidly to combine ingredients, but you don't need that in your life. No, if you're at home making emulsions, the real key is having a good whisk, blender or food processor, and an element that is neither liquid nor fat to help bring it all together. Here are a couple of common examples of emulsions beyond the vinaigrette:  

Pan sauce

You just cooked protein in a cast-iron pan, and there's some juice and roasted goodness left in there. Add butter, stock, wine and herbs, then whisk vigorously to emulsify. There are also some other things you can do to help the sauce achieve a rich, velvety consistency. First, use homemade stock you simmered with lots of bones; the gelatin from the bones helps the fat and liquids combine. You can also add some cornstarch to thicken it and make it clingier, but make sure you sift it in, continually whisking as you add it, so you don't get lumps.Salad dressingMy favorite trick for getting a salad dressing to emulsify is to add a little mustard. Dijon works best for vinaigrettes, but depending on what you're making, feel free to get creative and experiment with others (I've used every type of mustard in all kinds of dressings). Then put all your ingredients in a glass jar with a tight-sealing lid, and shake vigorously to create a smooth emulsion.

I chatted with chef and emulsion master Francis Derby of The Cannibal Beer & Butcher in NYC for a chef's perspective on this technique and its application. Which emulsion do you use most?

The emulsion we use the most right now is béarnaise sauce, a classic variation on hollandaise. We make ours in a Vitamix blender using the speed of the blade to make a strong emulsion and heat the sauce at the same time.

Do you have a go-to emulsifier that you use?

I use different ones for different applications. Each emulsion is different. Sometimes it's egg yolk, mustard, gelatin or xanthan gum. There are so many different applications for each emulsifier.

What do people get wrong when making emulsions at home?The most typical way to break an emulsion is adding fats too quickly. You need to give the base of the sauce time to "absorb" the oil. Go too fast and you will end up with a broken mess that looks like scrambled eggs. There's no way to  go back from there; you just have to start over at that point. So it's important to take your time. That's a good tip. Any other emulsion tips for home cooks?When making cold emulsions, like the pork mixture for mortadella, keep everything as cold as possible. This helps keep the emulsion stable. You can even go as far as to put the mixer parts in the fridge before you begin.I can only imagine what my girlfriend would say if she came home to find the blender in the fridge. What's your secret for a perfectly emulsified pan sauce?For pan sauces, I add emulsion to the reduction. So for a simple chicken pan sauce, in place of butter, I will use an already emulsified beurre fondue [melted butter blended with water]. This is why you start with something that's already stable.That's smart. What about salad dressing?Mustard is always a great way to keep salad dressings emulsified. If it's not the flavor you're after, then using a very small amount of xanthan gum will help to bring it together. Xanthan is very strong, so .25% of total weight will do it. That's just about the very tip of a small paring knife to about a quart of dressing. Using too much will make your dressing too viscous and almost gooey.Any tips for homemade mayonnaise?Go slowly!"Emulsion" and "emulsification" are sort of weird words. If you could make up a new term, what would it be?Haha, I have no idea. "Slow, smooth fatty cream?"