Simmer

To simmer means to cook just below the boiling point, when the surface of the simmering liquid shows occasional bubbles and a little movement but not much. We use this technique for gentle cooking. Recipes that call for simmering often specify whether the pot should be covered or uncovered, or partially covered. This is not as mysterious as it appears: if long simmering is to reduce or thicken and concentrate flavor, then the pot needs to be uncovered so that water can cook off in the form of steam. If the simmering is to cook food or blend flavors without losing liquid, then the pot needs to be completely or partly covered. Grains like rice are simmered in tightly covered pots because the point is to let the grain absorb the liquid and not to let it escape into the air.