An emulsion is a stable dispersion of two immiscible liquids — typically fat and water — where droplets of one are suspended in the other. Without an emulsifier, oil and water separate in seconds. With the right emulsifier at the right concentration, an emulsion can remain stable for days, weeks, or indefinitely. Understanding emulsification at the molecular level transforms sauce-making from a sequence of memorised steps into a set of physical principles applicable across every fat-water combination in the kitchen.
**Temperature and emulsification:** - Lecithin emulsifiers work most effectively in the range of 55–75°C. Below this range, the fat is too viscous; above it, proteins begin to denature and destabilise the emulsion. This is why hollandaise is made at 60–65°C and breaks above 75°C. - Cold emulsions (mayonnaise, vinaigrette) work because at room temperature, the fat droplets are liquid enough to disperse but viscous enough to remain in suspension. **The role of mechanical energy:** Emulsions require mechanical energy to create — whisking, blending, or shaking forces the oil and water together into small droplets while the emulsifier molecules rush to coat the new interfaces. A hand whisk creates droplets approximately 100–300 microns in diameter. A high-shear blender creates droplets 1–10 microns — the smaller the droplets, the more stable the emulsion (more surface area for emulsifier molecules to coat, less tendency to coalesce). Decisive moment: The first tablespoon of oil in mayonnaise or the first addition of butter in hollandaise — the moment when the dispersed phase (oil/butter) is being introduced to the continuous phase (egg-acid mixture). At this point the emulsifier concentration must be sufficient to coat the incoming droplets immediately. If oil is added too rapidly before the emulsion is established, the oil droplets exceed the emulsifier's coating capacity and the emulsion breaks. The establishing of the emulsion in the first tablespoon determines whether the rest can proceed at speed.
— **Emulsion breaks immediately on oil addition:** The emulsifier concentration is insufficient (not enough yolk, not enough lecithin), or the phases are incompatible in temperature. In hollandaise: butter too warm, yolks too cool. — **Emulsion breaks mid-way:** Temperature exceeded the stability window (hollandaise above 75°C), or oil was added too rapidly and droplet size exceeded emulsifier coverage. — **Emulsion appears stable but weeps within hours:** The droplet size is too large for long-term stability — larger droplets coalesce gradually. Made in a blender rather than by hand? Counterintuitively, a blender-made vinaigrette is often more stable because the smaller droplet size.
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