We’ve all heard the phrase “oil and water don’t mix.” It’s true—and it comes down to basic chemistry. Water molecules are polar, meaning they have slight electrical charges that attract one another. Oil molecules are nonpolar and hydrophobic (literally, “afraid of water”), so they repel water molecules rather than blend with them.
But in cooking, we’ve found ways to make these opposites coexist. The result of these coexisting opposites are emulsions—a creamy, stable mixture of two otherwise incompatible liquids. Think of mayonnaise, hollandaise, vinaigrettes, or even milk. These mixtures don’t blend on their own; they’re mechanically and chemically stabilized to keep their smooth texture. However, emulsions are metastable: they’ll eventually separate back into oil and water unless you take the right steps to hold them together.
How Emulsifications Work
Creating an emulsion is more than just mixing. It’s about breaking one liquid (like oil) into tiny droplets and dispersing them evenly through another (like water). The phase that forms the base of the mixture is the continuous phase, while the dispersed droplets make up the dispersed phase.
There are two main types of emulsions:
- Oil in water (O/W)—Oil is suspended in water. Examples include milk, cream, and mayonnaise.
- Water in oil (W/O)—Water is suspended in oil. Classic examples include butter and margarine.
Emulsifiers/stabilizers are the unsung heroes that hold these emulsions together. They are ingredients that stabilize the interface between oil and water, preventing the droplets from coalescing. Egg yolks, casein proteins (a kind of milk protein), and modern surfactants are all emulsifiers that perform this function—often in very different ways, which you can learn more about in Modernist Cuisine Vol. 4:202.
Emulsions are everywhere, even in foods we might not immediately recognize as such. Here are a few everyday examples you may not have considered:
- Chocolate uses lecithin, casein (from milk powder), or polyglycerol polyricinoleate as stabilizers
- Mountain Dew (and other sodas) uses gum arabic as an emulsifier to keep flavor and colorings evenly distributed (these are considered nanoemulsions)
- Ice cream is a complex emulsion and foam stabilized by dairy proteins, lecithin from egg yolks, and semisolid droplets of fat that trap air bubbles
- Hot dogs are held together by myosin protein from meat
Methods of Emulsifying
At its core, emulsification is about breaking down one liquid into microscopic droplets and blending it with another. This blending can be done in several ways:
- Whisking or stirring—Works well for small-scale emulsions like vinaigrettes.
- Blending—A high-speed blender or immersion blender can create smaller droplets and a more stable emulsion. Hand blenders tend to do well with beurre blanc and hollandaise, while the household blender is better for mayonnaise and vinaigrettes.
- Homogenizing—We love a countertop rotor-stator homogenizer for making fine emulsions that are incredibly stable, but they are best for existing emulsions. Unless you have a high-volume use for them, it is difficult to justify their steep cost at home.
While mechanical force can start the process, it’s the presence of an emulsifier that keeps the emulsion stable. Thickeners like xanthan gum or starches can also help by increasing viscosity, making it harder for droplets to move and combine.
Understanding Emulsifiers
A wide variety of surfactants and stabilizers makes it easier to produce stable emulsions. The names of these ingredients might be new to you; most of them are no more or less processed than salt, baking soda, and other more common ingredients. Many are derived from natural sources such as seaweed and starch or animal collagen, and can be purchased online from specialty shops like ModernistPantry.com—or found in stores if you’re looking for more common options like xanthan gum or gelatin. You can familiarize yourself with some different emulsifiers below.
- Agar is a seaweed-derived gelling agent often used in products like olive oil margarine. It performs well in emulsions of varying viscosities.
- Carrageenan is another seaweed-based option, which is best used in cold dairy applications, such as American cheese slices. It offers stability without the need for heat.
- Gelatin, made from animal collagen, can only be used in cold preparations and is commonly seen in desserts like Jell-O or in whipped creations like Chantilly cream.
- Gellan gum works best in nonacidic solutions and creates a stable, appealing texture even in thick emulsions, such as a beef suet mousseline.
- Guar gum, made from legumes and pregelatinized starch, often derived from corn or potatoes, can both be used to stabilize emulsions like hazelnut cream or margarine.
- Sodium alginate, another seaweed derivative, excels in dairy-based emulsions and is used in products like emulsified sausage, but it can impart a strong flavor if overused.
- Xanthan gum, produced through fermentation, is one of the most effective and versatile thickening agents—ideal for making mayonnaise—but, like some others, may result in a slimy or gummy texture when used in excess.
With so many emulsifiers available, choosing the right one depends on your desired texture, temperature conditions, and flavor profile. Once you get familiar with their properties, they can become powerful tools in your Modernist kitchen.
Dairy Emulsions
Milk, itself an emulsion straight from the cow, is the foundation of all dairy-based emulsions. Butterfat (also called milkfat) is suspended in water, and the emulsion is stabilized by casein protein. But it is not stable for long because it is prone to a type of emulsion failure named creaming, for the resulting cream that rises to the top of the milk. But with the application of powerful modern tools and ingredients, dairy emulsions can now exist in environments not formerly possible. Beurre blanc, a delicate and fussy sauce, used to require à la minute preparation. With an emulsifier, it can be made well in advance and held in a water bath, or even chilled and reheated if necessary.
Compound butters often are used as a flavorful finish on grilled steaks or fish fillets, but they fail, or break, on contact with hot food. In contrast, our Montpellier butter melts into a luscious, fully emulsified butter sauce (find the recipe in Modernist Cuisine at Home, p. 120 / Modernist Cuisine Vol. 4:219).
We also love the consistency of melted processed cheese—but dread the flavor. By creating a stable cheese emulsion from tasty varieties like Gruyère and white cheddar, we are able to marry taste to texture for the perfect cheeseburger topping as well as create incredible mac and cheese.
We use sodium citrate (an emulsifying salt) to make our Perfectly Melting Cheese Slice, enabling any cheese slice to melt as perfectly as American cheese does. This recipe can be found on page 317 of Modernist Cuisine at Home and in Modernist Cuisine Vol. 4:224.
One of our most popular recipes of all time is our Mac and Cheese, which also uses sodium citrate to create a texture as smooth as American cheese but as complex and intense in flavor as any of your favorite cheeses. Try the recipe for yourself!
How Emulsions Fail
No matter how precisely an emulsion is made—even with a high-pressure homogenizer—it is never truly permanent. Given enough time, every emulsion will eventually separate, sometimes quickly (as anyone who’s wrestled with splitting mayonnaise knows).
Emulsions can fail in several distinct ways:
- The droplets may remerge as they bump into each other and form larger ones, leading to creaming in oil-in-water (O/W) emulsions and sedimentation in water-in-oil (W/O) emulsions.
- Weak or insufficient emulsifiers may allow droplets to clump back together.
- Excessive agitation can destabilize the emulsion after it’s formed.
- Temperature shifts—especially heating or sudden cooling—can alter texture and cause breakage, as seen when a sauce that looks perfect off the heat falls apart when reheated or placed on a hot surface.
- Time itself eventually causes all emulsions to break down.
Most emulsions fail due to a combination of these forces, each compounding the others, though in some cases—such as clarifying stocks or producing nonfat milk—breakage is the desired outcome. In general, emulsions begin to break when heated beyond 70 °C / 158 °F, though exceptions exist.
Other Emulsion Highlights
Modernist Cuisine at Home dives into many recipes for emulsions, but one of our favorites is jus gras—a rich meaty sauce made by emulsifying savory jus with rendered fats, like chicken fat or fish oil. Try a simplified version here, or find the full recipe on page 93.
Oil-and-water emulsions like vinaigrettes are trickier without eggs or dairy. Whisking oil and vinegar with mustard or garlic can work, but it often separates quickly. Blending creates smaller droplets and helps it last longer. Add an emulsifier and the emulsion holds even better—see our Modernist Vinaigrette on page 117.
Emulsions may be rooted in complex chemistry and physics, but their impact in the kitchen is simple: luscious sauces, creamy textures, and dynamic flavor combinations. Whether you’re whisking a vinaigrette or using a homogenizer to create a silky foam, emulsions are a powerful tool in any cook’s repertoire. With a little experimentation—and the right emulsifier—you can master the delicate art of oil and water.
FURTHER READING
- Montpellier Butter—Modernist Cuisine at Home, p. 120 / Modernist Cuisine Vol. 4:219
- Perfectly Melting Cheese Slice—Modernist Cuisine at Home, p. 317 / Modernist Cuisine Vol. 4:224
- Silky Smooth Macaroni and Cheese—Modernist Cuisine
- “Fat Free” Mac and Cheese—Modernist Cuisine at Home, p. 315
- Egg Emulsions—Modernist Cuisine Vol. 4:226
- Mayonnaise—Modernist Cuisine at Home, p. 108 / Modernist Cuisine Vol. 4:226
- Sous Vide Hollandaise—Modernist Cuisine
- Home Jus Gras—Modernist Cuisine at Home, p. 93 / Modernist Cuisine Vol. 4:237
- Simplified Jus Gras—Modernist Cuisine
- Modernist Vinaigrette—Modernist Cuisine at Home, p. 117 / Modernist Cuisine Vol. 4:231