If you’ve ever made mayonnaise, whipped up a vinaigrette, or poured cream into coffee, you’ve already worked with an emulsion — even if you didn’t realise it.
An emulsion happens when two liquids that normally don’t mix (like oil and water) are blended into one smooth mixture. It sounds simple, but it’s one of the most useful and sometimes frustrating parts of cooking. When it works, you get creamy dressings, glossy sauces, and smooth textures that hold together beautifully. When it doesn’t, you’re left with something that separates, curdles, or refuses to blend, no matter how much whisking you do.
The science behind emulsions isn’t overly complicated. It’s mostly about noticing how ingredients react, and how small changes (in order, speed, or temperature) can change everything.
How emulsions work and why they matter in cooking
Oil and water don’t naturally mix. One repels the other, forming tiny droplets instead of a uniform blend. An emulsion is what happens when one liquid is broken into very small droplets and dispersed evenly throughout the other.
There are two main types of emulsions you’ll find in cooking:
- Oil-in-water emulsions, where oil droplets are dispersed in water (examples include milk, cream, or mayonnaise).
- Water-in-oil emulsions, where water droplets are suspended in oil (examples include butter and margarine).
In both cases, you need energy (from whisking, blending, or shaking) to break one liquid into droplets, and something to hold it all together so it doesn’t separate again. That “something” is called an emulsifier.
The role of emulsifiers
Emulsifiers are the peacekeepers of the kitchen. They help oil and water coexist.
On a molecular level, emulsifiers have two sides — one that loves water (hydrophilic) and one that loves oil (hydrophobic). When added to a mix, they coat the droplets and prevent them from clumping back together.
You probably already use emulsifiers without realising it.
Here are a few common ones found in everyday cooking:
- Egg yolks – contain lecithin, a natural emulsifier that helps stabilise mayonnaise and hollandaise sauce.
- Mustard – its compounds help keep vinaigrettes stable.
- Honey – helps stabilise dressings mainly by increasing viscosity; trace proteins and colloids can assist, but it isn’t a strong emulsifier.
- Garlic – when crushed, its polysaccharides and fine particles help stabilise emulsions. Traditional aioli relies on this; many modern versions add egg yolk.
- Dairy – milk proteins can stabilise mixtures like cream sauces or ice-cream bases.
Even a little emulsifier can make a big difference. Without it, oil droplets eventually merge back together and separate from water.
How emulsions form
Creating an emulsion is about balance — the right ratio of oil to water, enough energy to disperse droplets, and a stable emulsifier to keep everything in place.
Here’s what happens step by step:
- You start with two liquids that don’t mix.
For example, oil and vinegar in a salad dressing. - You apply force.
Whisking, blending, or shaking breaks one liquid into tiny droplets and spreads them throughout the other. - You stabilise the droplets.
The emulsifier coats each droplet so they don’t stick together again.
The smaller the droplets, the smoother and more stable the emulsion will be. That’s why a blender or food processor can make mayonnaise hold together more easily than whisking by hand — it creates finer droplets.
Temporary vs. stable emulsions
Not all emulsions are designed to last.
- Temporary emulsions form quickly but separate soon after. A simple vinaigrette made by whisking oil and vinegar without mustard is a classic example. It looks uniform for a few minutes, then the layers settle.
- More stable emulsions hold their structure for longer. Mayonnaise, hollandaise, or a well-made aioli stay smooth because they contain emulsifiers and fine droplets that resist separation. No emulsion is truly permanent; they just separate more slowly.
Both types have their place in cooking. A vinaigrette that naturally separates can be re-blended with a quick shake, and its lighter texture might actually suit some salads better than a thick, stable dressing.
Why emulsions split
Anyone who has watched a sauce curdle or a dressing separate, knows how frustrating it can be. Emulsions are delicate systems. When they “split,” it means the oil and water phases have separated again.
Common reasons include:
- Too much oil added too quickly. The emulsifier can’t coat the droplets fast enough.
- Temperature issues. Some emulsions, like hollandaise, rely on gentle heat. Too hot, and proteins in the egg yolk coagulate, causing curdling. Too cold, and the mixture won’t form. Keeping hollandaise around 60–70 °C prevents this.
- Wrong ratios. If there’s far more oil than water, the structure collapses.
- Not enough emulsifier. The stabilising agent simply runs out of capacity to hold things together.
The good news: a split emulsion isn’t always a lost cause.
How to fix a broken emulsion
Most emulsions can be rescued with a little patience and technique.
Here’s how:
- Add a teaspoon of water or lemon juice. Slowly whisk the broken mixture into the new liquid, drop by drop. The extra water phase gives the emulsifier room to rebuild the structure.
- Use a fresh egg yolk. Start with the yolk, then gradually whisk in the split mixture as if you were making mayonnaise from scratch.
- Add mustard or a stabiliser. For dressings or sauces, a little mustard can help bring everything back together.
If you’re making a sauce that requires heat (like hollandaise), moving the bowl off the heat immediately can stop further separation before it gets worse.
The science of stability
Stability is what separates a creamy sauce from an oily mess. Once the emulsion forms, maintaining it depends on a few factors:
- Droplet size: smaller droplets stay suspended longer and resist separation.
- Viscosity: thicker liquids slow down droplet movement, reducing the chance of them merging.
- Temperature: cooler emulsions are often more stable, which is why mayonnaise firms up in the fridge.
- Proper ratios: balance between the oil and water phases keeps the structure consistent.
That’s also why emulsions in food styling can behave differently under lights or camera heat — once the temperature changes, the structure shifts.
Everyday emulsions you already know
Even if you don’t call them emulsions, they’re everywhere in your kitchen.
- Mayonnaise: a classic oil-in-water emulsion held together by lecithin and proteins in egg yolks. The continuous phase is the water from the yolk and acid; oil becomes dispersed droplets coated by those emulsifiers.
- Vinaigrette: oil and vinegar, sometimes stabilised with mustard or honey.
- Aioli: traditionally made with garlic; many versions include egg yolk for extra stability.
- Butter: a water-in-oil emulsion — tiny water droplets suspended in fat.
- Ice cream: an emulsion stabilised by milk proteins and sometimes egg yolks.
- Sauces with dispersed fat: Alfredo and similar sauces act as emulsions stabilised by dairy proteins. Béchamel’s smoothness comes mainly from starch-thickened milk with fat dispersed through the matrix.
Understanding that these all rely on the same basic chemistry helps you control texture and flavour more precisely.
When emulsions break intentionally
Sometimes, you want them to separate. Certain dressings and sauces are designed to have a loose, layered texture that you mix just before serving. Think of a simple oil-and-vinegar dressing that leaves streaks of flavour on the plate, or a browned butter sauce where separation creates richness and contrast.
Knowing how to stabilise an emulsion also means you know how to control it — choosing when to keep it together and when to let it fall apart.
A bit of chemistry (without the lab coat)
On a molecular level, an emulsion is about surface tension and energy. Oil and water resist mixing because their molecules are polar opposites — water is polar, oil is non-polar. Whisking forces oil into tiny droplets surrounded by water, but they naturally want to reunite.
Emulsifiers work by reducing the surface tension between the two. The hydrophobic side of the molecule sticks to oil, and the hydrophilic side faces water. This creates a sort of protective shell around droplets, keeping them evenly distributed.
Over time, gravity and molecular motion can still cause the mixture to separate, but good technique, proper ratios, and the right emulsifier slow that process dramatically.
Why temperature matters
Temperature can make or break an emulsion.
Warm ingredients blend more easily because viscosity decreases — the liquids flow better and disperse faster. But if the heat rises too high, emulsifiers like egg yolks can denature and coagulate, breaking the structure.
Cold emulsions (like salad dressings or mayonnaise) are more stable once chilled, but harder to form if the oil is too cold and thick.
Room-temperature ingredients are often the safest starting point. Consistent temperature means everything mixes evenly, and the emulsifier can do its job without shock or stress.
The visual side: why emulsions look so good
Beyond taste and texture, emulsions make food look alive. That sheen on a perfectly dressed salad, the creamy consistency of a sauce dripping from a spoon, the glossy top of a chocolate ganache — all come from stable emulsions catching and reflecting light.
For food photographers and stylists, this matters. An emulsion that holds together means a consistent look across shots and time. Knowing how long it stays glossy or when it begins to dull helps plan the timing of every frame.
If a sauce looks “split” on camera, it’s not just about visual appeal — it signals instability. A smooth, even emulsion communicates balance, freshness, and care.
Why emulsions matter for recipe development
When you develop recipes, emulsions are a tool for both structure and flavour. They can trap aromas, carry fat-soluble flavour compounds, and change mouthfeel. The same basic principle that makes mayonnaise creamy can also be used to make smooth soups, desserts, or even plant-based alternatives.
Understanding how emulsions form and stabilise helps troubleshoot common problems:
- A sauce that feels greasy likely has too much oil for its water content.
- A dressing that tastes dull might need acidity or mustard to hold it together.
- A curdled soup or split curry could be fixed by adjusting the temperature and stirring method.
Once you see emulsions as part of food’s natural chemistry, you start to work with them, not against them.
The simplicity behind the science
At its heart, an emulsion is just two liquids learning to get along. The more you cook, the more you start recognising when something needs balance — a little acid, a slower pour, a whisk held for a few seconds longer.
That awareness builds confidence. You stop treating “split” sauces as failures and start treating them as part of the process.
Cooking with this kind of understanding doesn’t remove creativity — it gives you more control. You can adjust texture, shine, and flavour on purpose, rather than by chance.
Want to learn more?
Curious about how chemistry shapes everyday cooking? Visit the Food and Food Science section of this blog for more simple, science-based reads — like how acidity changes flavour or what happens when you bake, boil, or roast food.
If you’re a food or wellness brand looking to blend creativity and science in your visual content, I can help. With nearly nine years of experience in food photography, recipe development, and content strategy, I create work that’s both beautiful and built on real understanding.

