continuous phase

If the dispersed phase is the chocolate chips, the continuous phase is the dough that surrounds every chip and holds the whole cookie together. It is the unbroken, connected medium that fills all the space between the dispersed particles or droplets.

The continuous phase is also called the external phase. Because it forms one connected network, it determines what the product feels and behaves like: its viscosity governs how fast particles settle, and its nature (watery or oily) decides what mixes in and how the product spreads. You can dilute a disperse system only with a liquid that matches its continuous phase — adding water thins an oil-in-water emulsion but would break a water-in-oil one.

Identifying which phase is continuous is therefore a practical question. Simple tests help: a drop of an oil-in-water emulsion disperses readily when stirred into water, and a water-soluble dye stains its continuous phase uniformly, whereas a water-in-oil emulsion behaves the opposite way.