Oil and water do not mix by themselves. A little starch or egg makes them hold together.
An emulsion is oil broken into tiny drops inside water. Something must sit between them. Egg yolk, mustard, and starchy pasta water all do this job.
Japanese noodle sauces often use the starchy cooking water. Cooks call it the free thickener. Nothing is added and nothing is wasted.
Fat drops want to join back up. A binder coats each drop and keeps them apart. Without it, the sauce splits within a minute.
Start with the water side. Add oil in a thin line while stirring hard. Stop when the sauce turns cloudy and thick.
The first time I made a pan sauce, I poured all the butter at once. It turned into an oil slick.
| ❌ Symptom | 🔍 Cause | 💡 Solution |
|---|---|---|
| The sauce splits into oil and water | The oil went in too fast | Restart and add oil in a thin line |
| The sauce is thin and runs off | No binder in the pan | Add a spoon of starchy cooking water |
| The sauce turns grainy | The pan was too hot | Take the pan off the heat and stir |
