Simmering
Simmering cooks food in liquid held just below its boiling point, with gentle bubbles rising intermittently rather than a vigorous rolling boil.
Boiling point: The temperature at which a liquid's vapor pressure equals the surrounding pressure and it changes rapidly into gas. Simmering stays just below this temperature, though the boiling point varies with pressure.
Stewing: A method of cooking small pieces of food slowly in enough liquid to cover them. Stews are commonly cooked at a gentle simmer until their ingredients soften.
Liquid: A state of matter with fixed volume but no fixed shape, able to flow and take its container's form. Water, broth, and other cooking liquids carry heat to food during simmering.
Boiling: The rapid vaporization of a liquid throughout its volume when it reaches its boiling point. Boiling produces vigorous bubbles, unlike the restrained activity of a simmer.
Convection: Heat transfer through the movement of fluids such as liquids and gases. Circulating liquid carries heat around the pot and food during simmering.
Soup: A primarily liquid dish made by cooking ingredients in broth, water, or another liquid. A simmer extracts flavor while keeping soup ingredients from breaking apart too quickly.
Thermometer: An instrument that measures temperature. A thermometer can distinguish a low simmer from a boil when visual cues are unclear.
Poaching temperature: A low cooking-temperature range used to poach food, typically below the point where bubbles form steadily. This range falls below simmering and suits delicate foods such as eggs and fish.
Vapor pressure: The pressure exerted by a vapor in equilibrium with its liquid or solid phase. Rising vapor pressure helps determine when the cooking liquid reaches a boil.
Stock: A flavorful liquid made by simmering bones, vegetables, or other ingredients in water. A low simmer extracts flavor while limiting cloudiness and excessive emulsification.