What an emulsion is, and why it breaks
Oil and water separate the instant you stop stirring, because keeping them mixed costs energy their molecules would rather not spend. An emulsion is a temporary state where one is forced into tiny droplets suspended inside the other, and it holds only as long as something is standing guard at the surface of every droplet.
That guard is called an emulsifier. It is a molecule with one end that is happy in fat and one end that is happy in water, so it sits at the boundary of every droplet, facing both ways at once, and stops the droplets finding each other and merging back into two separate layers. Egg yolk is the classical kitchen emulsifier because it is unusually rich in exactly this kind of molecule — chiefly lecithin. Without an emulsifier, oil and water mixed by force will separate again within seconds; with one, the same mixture can hold for hours, or indefinitely.
An emulsion breaks — cooks say it "splits" or "curdles" — when the droplets are given a chance to find and merge with each other faster than the emulsifier can keep them apart. That happens in a small number of predictable ways: too much oil added too fast, so there are more droplets than the emulsifier on hand can coat; too little emulsifier for the amount of fat being asked to disperse; heat applied so violently that the emulsifier itself is damaged (an egg yolk that scrambles can no longer emulsify anything); or simple cold, which stiffens fat into a state that will not disperse into fine droplets at all. Every rescue technique on this page works by doing the one thing that actually fixes a split: starting a fresh, small, stable emulsion and feeding the broken mixture into it gradually, rather than trying to persuade the broken mixture to fix itself.
An emulsion is not a mixture you make once. It is a state you maintain, one droplet at a time, for as long as the sauce needs to hold.
The first law of the sauce station, continuedThe emulsifiers a kitchen has
Four ingredients do almost all the emulsifying work in a French kitchen, and knowing which is doing the work in a given sauce tells you exactly how much fat it can carry and how it will fail.
| Emulsifier | Strength | Found in |
|---|---|---|
| Egg yolk | Strong — one yolk holds up to 200 ml oil | Mayonnaise, hollandaise, béarnaise, aïoli when made the modern way |
| Mustard | Moderate, but very stable and heat-tolerant | Vinaigrette, and stiffens mayonnaise further when added alongside egg |
| Butter's milk solids | Weak — carries only a small amount of extra fat | Beurre blanc, monter au beurre, where whole butter is whisked into a reduction |
| Garlic (pounded to a paste) | Moderate, and flavours as it emulsifies | Aïoli in its oldest form, before egg yolk became standard |
Notice the huge gap in strength between egg yolk and butter. This is why beurre blanc collapses so much faster than hollandaise if you are careless with it — the milk solids in butter are a genuinely weak emulsifier doing a small job (holding melted butter together as a sauce), while the lecithin in a yolk is a strong emulsifier holding an enormous quantity of oil relative to its own volume. Treat beurre blanc with more caution, not less, because it has less margin for error.
Vinaigrette and the mustard trick
The simplest emulsion in the kitchen and the one most people make without realising it is one. Classical ratio: three parts oil to one part acid (vinegar or lemon juice), by volume.
- Whisk the mustard in first. A teaspoon of Dijon whisked into the vinegar, salt and pepper before any oil is added gives the emulsifier a head start and produces a vinaigrette that holds together in the bowl for a genuinely long time rather than separating within a minute.
- Add the oil in a thin, steady stream, whisking constantly. The same principle that governs mayonnaise below, at a smaller scale and with far more tolerance for error — a split vinaigrette is fixed by ten seconds of hard whisking, or by shaking it in a jar.
- Taste before dressing anything. A vinaigrette should taste slightly too sharp on its own spoon; leaves mute the acidity once dressed.
A jar with a tight lid, shaken hard, makes a passable vinaigrette without any whisking at all — the agitation does the same job as the whisk, just more roughly, and a well-mustarded vinaigrette tolerates it. It is the one emulsion on this page where a shortcut is genuinely fine.
Mayonnaise, by hand
Mayonnaise is a large amount of oil suspended, drop by drop at first, in a small amount of egg yolk. It needs no machine of any kind, and making it with a whisk and a bowl teaches you the whole logic of every emulsion on this page. Deliberately: this school teaches it by hand and does not offer the blender method, because the pace a hand whisk forces on you is exactly the pace that prevents a split.
Steady the bowl
Set a mixing bowl on a folded damp cloth, so it cannot slide as you whisk one-handed. This single trick is what makes hand mayonnaise practical — without it you are fighting the bowl as much as the sauce.
Whisk the yolk, mustard and a little acid together
One egg yolk, a teaspoon of Dijon mustard, a teaspoon of vinegar or lemon juice, a pinch of salt. Whisk thirty seconds until pale and slightly thickened. This base is where every drop of oil will land.
CueThe mixture lightens in colour and thickens just enough to coat the whisk.Oil in drop by drop, then a thin stream
Begin adding a neutral oil (or a mix of neutral oil and a little olive oil for flavour) genuinely one drop at a time for the first two tablespoons, whisking hard and constantly. Once the mixture has visibly thickened and taken on a pale, glossy look, the emulsion is established and you can move to a thin, steady stream, still whisking without pause.
CueThe moment it "takes" feels sudden — the mixture goes from thin and slippery to noticeably resistant against the whisk within a few drops.Loosen and finish
As it thickens past the point of a stiff paste, whisk in a teaspoon of warm water or a little more acid to loosen it before continuing with oil — this keeps the emulsion from becoming so concentrated it turns fragile. Finish with salt, more acid to taste, and use within the day, kept cool.
A blender or stick blender makes mayonnaise in twenty seconds and is genuinely useful for a large batch. But it also disperses oil so fast that it papers over sloppy technique, and a beginner who only ever uses one never learns to feel an emulsion forming. Learn it by hand first; use the machine later, once you understand what it is doing for you.
Aïoli, rémoulade, gribiche, tartare
Mayonnaise is a base as much as a finished sauce. Almost every classical cold sauce in the French repertoire is mayonnaise (or a close relative) plus one deliberate addition.
- Aïoli, garlic mayonnaise. Pound two or three garlic cloves to a smooth paste with a pinch of coarse salt, using the flat of a knife blade as described in Knife Skills, then build the mayonnaise directly onto that paste instead of onto plain yolk. Olive oil, used in full here, gives it its traditional weight and colour.
- Rémoulade. Mayonnaise finished with capers, cornichons and herbs (parsley, chervil, tarragon), all very finely chopped, plus a dash of anchovy essence in the classical version. The base for céleri rémoulade.
- Sauce gribiche. Built the other way round: chopped hard-boiled egg yolk, mashed to a paste and used as the emulsifier in place of raw yolk, then oil whisked in as normal, finished with the chopped white, capers, cornichons and herbs. Traditional with cold poached fish and calf's head.
- Sauce tartare. Mayonnaise with finely chopped cornichon, caper and shallot, and a good deal of chopped herb — parsley and chervil, classically, though many kitchens add chive. The everyday partner to fried fish.
Notice that all four use exactly the same emulsion, at exactly the same ratio, and differ only in what is chopped into it — which is the same lesson the sauce mothers teach on Sauce Making, applied to the cold side of the kitchen.
The warm family
The warm emulsions — hollandaise, béarnaise, beurre blanc — trade the raw stability of mayonnaise for something more fragile and, arguably, more delicious: melted butter held in suspension by egg yolk (hollandaise and béarnaise) or by butter's own milk solids alone (beurre blanc). All three are made over gentle, controlled heat, and all three need a bain-marie or its improvised equivalent.
Any pan and any heatproof bowl that nest together loosely will do. The two things that matter: the water beneath must never touch the base of the bowl, and it must never do more than shiver — a hard simmer sends up too much heat and too much moisture, either of which can cook the yolk before it has finished emulsifying the butter.
Hollandaise over a bain-marie
Butter, egg yolk, lemon, cayenne. The base of eggs Benedict and the classical partner to asparagus and poached salmon — and, technique for technique, the single best sauce to learn the whole warm-emulsion family from.
Clarify the butter, gently
Melt 150 g butter slowly in a small pan until it separates into a clear golden layer on top and milky solids underneath. Skim off any foam and pour off the clear butter, leaving the milky solids behind. This is not strictly necessary for hollandaise as the milk solids will still emulsify fine, but clarified butter gives a cleaner, more stable sauce and a purer colour.
Whisk yolks and a little liquid over the bain-marie
Two egg yolks and a tablespoon of water (or the classical reduction of vinegar and cracked pepper, cooled) in the bowl, set over the barely simmering water. Whisk constantly and vigorously, lifting the bowl off the heat every few seconds if it seems to be catching too fast.
CueThe mixture turns pale, doubles in volume, and leaves a visible ribbon trail across itself when the whisk lifts. This stage is called the sabayon and it is the whole foundation of the sauce.Add the warm butter, slowly at first
Off the direct heat now (bowl set on the damp cloth, not over the pan), add the warm clarified butter in a very thin stream, whisking constantly, exactly as with mayonnaise — a few drops at first, building to a slow stream as the emulsion establishes itself.
CueSame as mayonnaise: a sudden thickening and resistance against the whisk once the emulsion takes hold.Season and hold gently
Lemon juice, salt, a pinch of cayenne, whisked in at the end. If it needs to wait, keep the bowl over the barely warm (not simmering) water, whisking occasionally — never over direct heat, and never for more than twenty or thirty minutes, after which it is safer to make a fresh batch than to keep pushing an old one.
If at any point the mixture in the bowl looks like it is thickening into curds rather than a smooth cream, lift it off the heat immediately and whisk hard, off the heat, for a full ten seconds before deciding whether to continue. Heat that has scrambled a yolk cannot be undone by whisking; heat that has merely come close can often be saved by simply removing it in time.
Béarnaise and sauce mousseline
Béarnaise is hollandaise's savoury cousin, built the same way but with the sabayon flavoured by a hard reduction instead of plain water.
- Reduce first. Two tablespoons of finely chopped shallot, a tablespoon of chopped tarragon stalks, black peppercorns cracked, and 100 ml each of white wine and white wine vinegar, simmered together in a small pan until reduced to about two tablespoons of syrupy liquid. Strain, pressing the solids to extract everything, and cool slightly.
- Then follow hollandaise exactly, using the strained reduction in place of the plain water in the sabayon stage. Finish with plenty of freshly chopped tarragon and chervil, and no lemon — the vinegar reduction already supplies the acidity.
Sauce mousseline is hollandaise (or occasionally béarnaise) lightened at the very last moment with softly whipped cream, folded in gently off the heat. It is not whisked in like the butter — folding preserves the air already beaten into the cream, which is the entire point of the sauce and the source of its name.
Beurre blanc and beurre rouge
The most fragile sauce in this school, and the clearest possible demonstration of an emulsion held by nothing but butter's own milk solids — no egg at all.
Reduce shallot and wine hard
Two tablespoons of very finely minced shallot with 100 ml dry white wine (use red wine and a touch of red wine vinegar for beurre rouge) and a tablespoon of white wine vinegar, simmered in a small pan until reduced to little more than a tablespoon of thick, syrupy liquid — almost, but not quite, dry.
Lower the heat, add butter in small pieces
Turn the heat down to the gentlest possible simmer, almost off. Add cold, diced butter — around 150 g total — a piece or two at a time, whisking constantly, letting each piece melt into a creamy emulsion before adding the next rather than dumping it all in.
CueThe sauce should look like a pale, opaque, slightly frothy cream, never like clear melted butter. Clear and oily-looking means it has already begun to split.Pull off heat before it looks finished
Beurre blanc has almost no thermal buffer — take it off the heat a little before you think it needs it, because the pan's residual heat will finish emulsifying the last pieces of butter regardless. Strain out the shallot if you want it perfectly smooth, though many kitchens leave it in deliberately.
Serve beurre blanc within minutes of making it, and never let it sit over any heat at all once finished — see Rescuing a broken emulsion below for what to do when, not if, it splits on you the first several times.
Temperature windows at a glance
Each emulsion has a narrow band of heat where it can actually form, bounded on the cold side by fat too stiff to disperse and on the hot side by the emulsifier being destroyed. Reading these cues correctly matters more than reading a thermometer, because a thermometer cannot tell you the texture in the bowl.
| Sauce | Working temperature | Visual cue it is right | Visual cue it is failing |
|---|---|---|---|
| Vinaigrette | Cool, room temperature | Glossy and slightly thickened when whisked | Separates within a minute of standing still — normal; re-whisk before use |
| Mayonnaise | Room temperature ingredients, no heat | Pale, thick, holds a soft peak on the whisk | Thin and slippery, oil pooling at the edge of the bowl |
| Hollandaise | Sabayon warm to the touch, never hot; finished sauce barely warm | Sabayon leaves a ribbon trail; finished sauce is thick, pale yellow, glossy | Yolk mixture looks grainy or lumpy — it is scrambling |
| Béarnaise | Same as hollandaise | Same as hollandaise, flecked green with herb | Same as hollandaise |
| Beurre blanc | Barest simmer, almost off the heat | Pale, opaque, faintly frothy cream | Turns clear and oily, or the butter separates into visible fat |
Across every warm emulsion, oil or melted butter must go in slowly at first and can go in more quickly later, and the reason is the same reason in every case: at the start there is very little emulsifier already spread across very little surface area, so each new drop of fat is competing for a small, easily overwhelmed supply. Once a stable base of small droplets exists — once the sauce has visibly "taken" — that same emulsifier is already coating a huge surface area of tiny droplets, and new fat has an easier time finding a droplet to join rather than pooling on its own. The curve is steep at the start and flattens fast; that is the whole reason the early drops matter so much more than the later stream.
Rescuing a broken emulsion
Mayonnaise has split — thin and oily, oil pooling
Oil added too fast for the yolk to disperse, or the yolk itself was too cold and stiff to take oil readily.
Fix, method oneIn a clean bowl, whisk a fresh egg yolk (or a teaspoon of warm water, or a teaspoon of mustard) until smooth, then whisk the split mixture back in very slowly, exactly as though it were the oil in a fresh mayonnaise.
Mayonnaise won't come back with a fresh yolk
Sometimes the split mixture is too cold or too much has separated for a plain yolk to catch it quickly.
Fix, method twoWarm the split mixture very slightly (a few seconds over the lowest possible heat, off again immediately) before whisking it into the fresh yolk — warmth alone often loosens fat enough to disperse again.
Mayonnaise is stubbornly split even after both fixes
Rare, but it happens with an old or very cold yolk.
Fix, method threeWhisk a teaspoon of Dijon mustard alone in a clean bowl, then add the split mixture in a very thin stream — mustard's own emulsifying power is often enough to rescue what egg yolk alone could not.
Hollandaise has split — grainy, or oil floating on a thin liquid
The sabayon overheated and partially scrambled, or the butter went in too fast.
FixIn a clean bowl, whisk a fresh egg yolk with a teaspoon of warm water over the bain-marie until it ribbons, then whisk the split hollandaise in very slowly, as though it were the butter. If the yolk itself has visibly scrambled into curds, strain those out first — they will not smooth out no matter how long you whisk.
Beurre blanc has broken — clear, oily, separated
Too much heat, too much butter added at once, or the pan left over direct heat too long.
FixOff the heat, whisk in a teaspoon of cold water or cream — this alone often re-forms it, because it gives the milk solids a small amount of fresh liquid to grip. If that fails, start a fresh teaspoon of cream warmed gently in a clean pan and whisk the broken sauce into it gradually.
Vinaigrette separates in the jar
This is normal and not a fault — vinaigrette without enough mustard will always settle given time.
FixShake or whisk again immediately before dressing. If it separates within seconds every time, add more mustard next time; it is the fix that actually lasts.
Making hollandaise for six, without it splitting
Hollandaise is a famously bad sauce to make in advance because it neither reheats nor waits well by the usual rules — but a dinner for six cannot be made à la minute, one spoonful at a time, without the cook missing the whole first course. The solution is not a trick; it is simply respecting the sauce's actual tolerance.
- Scale the recipe up properly, do not just multiply blindly. For six, three or four yolks and 300 g clarified butter is plenty — a larger volume of sabayon is, if anything, slightly more stable than a small one, because it has more thermal mass and reacts less suddenly to heat.
- Make it twenty to thirty minutes before serving, not two hours. That window is the sauce's real limit. Anything held longer should be remade rather than nursed.
- Hold it off the heat entirely, over lukewarm — not hot — water, whisking every few minutes. The bowl should feel comfortably warm to the back of a hand, never hot. This is the same discipline as the sauce-station habit of keeping any finished emulsion off direct heat, covered generally in Sauce Making.
- Loosen it just before serving. A hollandaise that has waited tends to thicken slightly as it cools; a teaspoon of warm water whisked in just before plating restores it to pouring consistency without any risk, since no more fat is being added.
Serving hollandaise or béarnaise for a larger table is really a scheduling problem dressed up as a cooking problem: make the sauce last, after everything else is essentially ready, and give it the shortest possible wait before it reaches the table.
Food safety with raw yolks
Mayonnaise, aïoli and gribiche use raw egg yolk and are never cooked afterwards. In most home kitchens, with good eggs and clean hands, this is a very low risk — but it is not zero, and it is not a risk worth taking with pregnant women, small children, the elderly, or anyone immunocompromised. Use pasteurised eggs for those guests, or serve them a cooked alternative instead.
- Buy eggs you trust and check the date. Fresher eggs carry lower risk and also emulsify better, which is a fortunate coincidence.
- Keep everything cold until the moment of use, then use promptly. Mayonnaise and its relatives should go straight into the refrigerator once made and be eaten within a day.
- Hollandaise and béarnaise are gentler on this point, since the yolk is warmed through in the sabayon stage even though it never reaches a full scramble — but they are still not fully cooked, and the same caution about vulnerable guests applies.
- Clean hands, clean bowl. The bacteria of concern travel on eggshell and on hands far more often than they start inside a fresh, intact egg — wash both before you begin.
Every emulsion on this page is the same short argument between fat and water, and every rescue on this page is the same short argument won a second time, in a clean bowl.
Les Émulsions