What emulsifies oil and water?

What emulsifies oil and water?

An emulsifier plus shear. An emulsifier is amphiphilic — one part oil-loving, one part water-loving — so it can sit at the oil–water border and coat tiny droplets so they don’t rush back into a slick. In the kitchen that usually means:

Oil and water alone will temporarily scatter when you shake them, then separate. The emulsifier is what slows that separation.

• Egg-yolk lecithin (and yolk proteins) — mayo, hollandaise
• Mustard particles (proteins + mucilage) — vinaigrette
• Mechanical force — whisk, blender, or a hard shake, to create fresh interface the emulsifier can cover

Will salt water emulsify with oil? What will emulsify salt-water and oil?

Salt alone will not. Dissolved salt (NaCl) seasons the water phase; it is not an amphiphilic emulsifier. Salt water + oil still separates unless you add a real emulsifier (mustard, yolk, etc.) and apply shear — same rules as plain water and oil.

Salt can change how some emulsifiers pack at the interface once an emulsion already exists, but it does not replace mustard or lecithin. If a recipe asks for salt in a vinaigrette, that is mostly for taste (and it can help mustard disperse) — the emulsifier is still the mustard or yolk.

Does acid emulsify oil and water?

No. In a vinaigrette, vinegar or lemon juice is the water side of the mix, not the emulsifier. McGee says a successful emulsion needs a third ingredient besides the two liquids: an emulsifier, such as egg yolk or ground herbs or spices, that coats the oil droplets and keeps them from merging. That’s why the vinaigrette below adds mustard. The Institute of Food Science and Technology’s oil-and-vinegar demo works the same way: plain oil and vinegar separate, and mustard is one of the added ingredients it tests to make the mix last longer.

Sources

• Harold McGee, On Food and Cooking (2004), “Sauces Thickened with Droplets of Oil or Water: Emulsions” — https://app.ckbk.com/reference/food00011c11s001e007/sauces-thickened-with-droplets-of-oil-or-water-emulsions
• Harold McGee, On Food and Cooking (2004), “Emulsifiers” — https://app.ckbk.com/reference/food00011c11s001e002se002se004se001/emulsifiers
• Institute of Food Science and Technology — emulsifiers have hydrophilic and hydrophobic ends; common kitchen examples egg yolk and mustard; butter/margarine = water dispersed in fat; milk/mayo/dressing = oil dispersed in water — https://www.ifst.org/lovefoodlovescience/resources/fats-and-oils-emulsification
• Serious Eats / J. Kenji López-Alt — hollandaise is a fat-in-water emulsion (same family as mayo) — https://www.seriouseats.com/foolproof-2-minute-hollandaise-recipe
• Serious Eats — mustard’s proteins and mucilage are amphiphilic and stabilize vinaigrettes — https://www.seriouseats.com/salad-vinaigrette-technique-11786636

Technique A — vinaigrette (forgiving)

1. 01Whisk 1 part acid (vinegar/citrus) + salt + 1 tsp mustard until even.
2. 02Stream in 3 parts oil while whisking hard (or shake in a jar).
3. 03Taste; adjust salt/acid.
4. 04If broken: new bowl + mustard spoon; slowly whisk broken mix back in.

Technique B — mayonnaise (tighter)

1. 01Yolk + pinch salt + splash acid + optional mustard in a bowl.
2. 02Whisk; add oil dropwise until it thickens, then in a thin stream.
3. 03Too thick? Whisk in a few drops of water.
4. 04Broken? Start a fresh yolk; stream the broken mayo in slowly as if it were oil.