A wort chiller is a heat exchanger designed to cool your wort to yeast pitch-able temperatures at a rapid rate, forming the cold break. The coil is attached to a garden hose or kitchen sink, where cool water runs internally through the coils and is immersed in the hot wort. The heat from the wort is conducted by the metal and expelled through the chiller's outlet tube, which cools the wort in an extremely efficiently manner. More info.