An emulsion is a stable mixture of two liquids that normally don't mix — typically oil and water. Mayonnaise (oil suspended in lemon juice/vinegar, stabilised by egg yolk lecithin), vinaigrette (oil and vinegar, temporarily emulsified by mustard), hollandaise (butter suspended in egg yolk and lemon), aioli (oil suspended by garlic), and beurre blanc (butter suspended in reduced wine/vinegar) are all emulsions. The emulsifier — the molecule that bridges oil and water (egg yolk lecithin, mustard mucilage, garlic compounds, casein in butter) — is the key to every one of these sauces. Understanding emulsification explains why mayonnaise splits, why hollandaise breaks, why cacio e pepe seizes, and how to fix all of them.
- **Add the oil slowly.** In any emulsion, the dispersed phase (oil) must be added gradually to the continuous phase (water/acid). Adding too much oil too fast overwhelms the emulsifier and the sauce breaks — the oil and water separate visibly. - **Temperature matters.** Hollandaise breaks above ~68°C because the egg proteins denature and can no longer stabilise the emulsion. Beurre blanc breaks if it gets too hot — the butterfat separates from the milk solids and water. Cacio e pepe seizes above ~70°C — the cheese proteins tighten. - **A broken emulsion can often be rescued.** Start a new emulsion with a fresh egg yolk (or a tablespoon of water, or a spoonful of mustard) and slowly whisk the broken sauce into it. The new emulsifier re-stabilises the old mixture. - **Every culture has its emulsion.** French = mayonnaise, hollandaise, beurre blanc. Italian = cacio e pepe cheese emulsion. Provençal = aioli (garlic-only emulsion). Middle Eastern = tahini (sesame paste in water). Japanese = ponzu-based dressings. The principle is universal; the emulsifier changes.
THE 2,000th ENTRY AND BEYOND — FILLING THE FINAL GAPS