Salt, Fat, Acid, Heat: Mastering the Elements of Good Cooking
Nosrat, Samin
Pages 168–177 cover the science and practical use of emulsions in cooking. Nosrat explains what an emulsion is — two normally immiscible liquids (fat and water) forced into a stable, creamy mixture — and walks through how to make and maintain common kitchen emulsions including vinaigrette, mayonnaise, and butter sauces. The section ends with a note that the most common way to break an emulsion is a temperature swing.
- An emulsifier (like mustard in vinaigrette or lecithin in egg yolk) acts as a molecular mediator, coating oil droplets so they stay dispersed in water rather than separating.
- For homemade mayonnaise: use room-temperature egg yolk, add oil one drop at a time until half the oil is incorporated, then add the rest more quickly; each yolk holds about ¾ cup of oil.
- Butter is itself an emulsion of fat, water, and milk solids — unusually stable across a wide temperature range (32°F–90°F), but melted butter is a broken emulsion that won't re-form.
- Temperature precision with butter matters: room-temp butter aerates cakes; cold butter preserves its emulsion for flaky pastry doughs; for a pan sauce, start with a warm pan and cold butter, swirl over medium-high heat, and serve immediately.
- Common kitchen emulsions listed: mayonnaise, hollandaise, vinaigrettes, butter/cream/milk, peanut butter and tahini, chocolate, and espresso crema.
- The most common way to break any emulsion is a temperature swing — each emulsion has its own comfort zone (e.g., heating a vinaigrette or chilling a beurre blanc will break it).