Emulsion

An emulsion is fat and water occupying the same spoonful without being a true solution. Left alone, they prefer to separate. A cook or a mammary gland delays that. Lecithin and other emulsifiers stabilize some systems; the right balance depends on the materials and process.

Milk is already one #

FAO: milk components exist as true solution, colloidal dispersion, or emulsion. Milk fat is the emulsion; if left to stand it precipitates or rises under gravity ¹. That cream line is the observation. Homogenized milk hides it; it does not repeal the two phases.

Casein is the other stability story — a colloid, not an oil droplet. Destabilize it with acid or rennet and you have Coagulation, not a broken vinaigrette.

Butter is the inversion you can legislate #

U.S. law: butter is the food made exclusively from milk or cream, or both, with or without salt and coloring, containing not less than 80 percent milk fat by weight ². Churning gathers the fat that was dispersed in cream into a continuous fat food with water trapped inside. The statute is an identity floor, not a recipe. Undershooting 80 percent is a labeling problem, not a whisking problem.

What to observe #

Look. A vinaigrette that was cloudy and one body becomes a slick of oil on water — broken. Mayonnaise that weeps oil has lost the hold Protein (from egg) was giving it. Do not upgrade that kitchen observation into an unsourced molecular diagram.

Feel. Milk fat in cheese is trapped in curd; FAO’s yield notes treat fat as something that mostly goes into the cheese if you do not lose it in the whey ¹. Greasy whey is fat that escaped the network.

Heat and acid both help an emulsion fail. So does time. A broken sauce is a quality failure. Fat is the ingredient class; Foam is gas in a film, not oil in water.