To emulsify is to convert two or more immiscible liquids into an emulsion — or for the mixture itself to become one. Oil and water do not mix, but vigorous agitation breaks one into droplets dispersed through the other, and an emulsifier — egg-yolk lecithin in mayonnaise, mustard in vinaigrette, milk proteins in cream — coats the droplets and stops them coalescing. The result is the whole family of emulsified foods: mayonnaise, hollandaise, vinaigrettes, ice cream, sausages. The cook’s skill lies in the addition rate — oil added too fast overwhelms the emulsifier and the sauce splits — and in temperature, which affects viscosity and stability. Emulsification is colloid science in the kitchen: creating order, droplet by droplet, from two liquids that would rather stay apart.