Food Emulsions 101: The Science Behind Creamy Sauces and Dressings

Emulsions are everywhere in your kitchen. Classic emulsions include mayonnaise, vinaigrettes, Hollandaise and Béarnaise sauces, and aioli. But did you also know that ice cream, nut milks, butter, and even chocolate are emulsions?

Understanding emulsions will help you prevent split sauces, create creamy textures, and combine ingredients that usually don't mix, giving you the ability to create unique textures and mouthfeels, and riff on different flavors in many of your favorite dishes.

Jump to:

• What Are Emulsions?
• The Secret Ingredients: Emulsifiers
• The Two Types of Emulsions
• Why Understanding Emulsions Matters in Cooking
• Related
• Sources

What Are Emulsions?

Simply said, an emulsion is a combination of two liquids that normally don't mix, like oil or fat and water.

For food science nerds out there: emulsions are droplets of one liquid dispersed in another unmixable liquid. When these incompatible liquids are forced to exist, they create thicker, creamier mixtures.

Let's look at a classic example: vinaigrette (like the ginger-lime one you make here for a ribbon carrot salad). At its core, a vinaigrette combines water (vinegar, lemon juice, lime juice, etc.) and fat (olive oil, bacon fat, walnut oil, canola oil, etc.). If you put your vinegar and canola oil in the same container, the separate into distinct layers to minimize contact with each other²:

Oil and water have different densities and oil molecules are also hydrophobic (water-repelling).

When you shake a vinaigrette, you temporarily for the oil to suspend within the vinegar, creating tiny droplets dispersed throughout the water. This is an emulsion in its most basic form--though without a mediator, these droplets quickly coalesce and separate.

These droplets quickly rejoin is because emulsions, by nature, are unstable (without assistance, that is!) because the molecules want to minimize surface contact with anything they don't mix with.

The Secret Ingredients: Emulsifiers

This is where emulsifiers save the day!

Emulsifiers stabilize an emulsion by acting as a bridge between oil and water. How? Thanks to their most important property: they're amphiphilic. This means that they contain both hydrophilic (water-loving) and hydrophobic (water-hating) or lipophilic (fat-loving) parts joined together.

One end of an emulsifier molecule bonds with water, while the other end bonds with oil, creating a barrier around the dispersed ingredient that prevents or at least hinders separation. THIS is how emulsifiers help maintain the emulsion's stability. What a peacekeeper.

Take our vinaigrette example: adding a teaspoon of mustard (which contains natural emulsifiers) and shaking the mixture like you mean it results in a dressing that says combined for much longer than one without an emulsifier.

Other common kitchen ingredients that contain emulsifiers include

• Aquafaba (the liquid from canned chickpeas or other beans)
• Avocado
• Tomato paste
• Tahini
• Egg yolks (contain lecithin, a very powerful emulsifier)
• Garlic paste
• Miso
• Honey

The Two Types of Emulsions

In any emulsion, one liquid forms the continuous phase (the surrounding liquid) while the other forms the dispersed phase (tiny spread out droplets).

But which ingredient is the continuous phase and which is the dispersed? There are two different ways to describe this:

1. Oil-in-water (O/W) - Droplets of oil dispersed throughout a continuous water phase
   • Examples- Mayonnaise, Hollandaise sauce, milk
2. Water-in-oil (W/O) - Droplets of water dispersed throughout a continuous oil phase
   • Examples - Butter, vinaigrettes

Oil-in-water emulsions typically have a creamier, less greasy mouthfeel than water-in-oil, which is why they're more common in sauces. I mean, who wants a mouthful of grease? 🥴

The type of emulsion is determined by:

• How its prepared - Adding oil slowly to egg yolks creates an oil-in-water emulsion (mayonnaise). Perhaps you know from experience what happens when you add the oil too fast or whisk too slowly, resulting in a broken oily mess. This is because the oil isn't getting properly dispersed into the continuous phase (the water from the egg and lemon juice).
• What type of emulsifier you're using: Emulsifiers that are more fat-loving are more likely to help form a water-in-oil emulsion; while an emulsifier that's more water-loving is more likely to help form an oil-in-water emulsion. (HLB [Hydrophilic-lipophilic balance])
• What ingredient you start with: The continuous phase is often the starting ingredient. Checks out in mayo, where the starting ingredients (egg and acid) are also the continuous phrase.
• And other factors

Emulsions can also be categorized by stability:

1. Temporary - Vinaigrettes (shake before use)
2. Semi permanent - Hollandaise sauce (stable for hours)
3. Permanent - Mayo (stable for days or weeks)

Why Understanding Emulsions Matters in Cooking

Understanding emulsions matters.

Instead of quickly separating oil-and-vinegar dressings, adding an emulsifier like mustard or egg yolk creates a more stable mixture that coats salads evenly and looks more appealing on the table during your dinner parties.

When making a pan sauce from the most beautiful roasted chicken drippings your very proud of, you could finish the sauce with butter (an emulsion technique called monter au beurre) that creates a velvety sauce that perfectly coats your food while adding richness.

Knowledge of emulsions can also prevent kitchen disasters. Adding oil too quickly can break mayonnaise. Not whisking continuously will fail to break up your dispersed phase ingredient. Overheating Hollandaise sauce will break down and denature your egg yolks, causing the sauce to break.

(Both a broken mayo and Hollandaise can be rescued by starting with another egg yolk [continuous phase] in a bowl, whisking it, then VERY SLOWLY adding the broken sauce [the liquid you're trying to disperse] in a VERY SLOW STREAM while WHISKING VIGOROUSLY. Video to come.)

When a recipe calls for "emulsifying" ingredients or warns against a breaking sauce, you'll know understand exactly what's happening at a molecular level--and how to get the perfect result (or fix less-than-perfect results)!

Stay tuned for upcoming emulsion articles, and in the meantime, happy experimenting!

Related

Looking for more articles on the hows and whys of food? Try these:

Sources

1. Emulsion. (2025, April 8). In Wikipedia. https://en.wikipedia.org/w/index.php?title=Emulsion&oldid=1284549784
2. McGee, H. (2007). On Food and Cooking: The Science and Lore of the Kitchen. Scribner.