A coffee percolator is a type of coffee pot.
The percolator consists of a pot with a small chamber at the bottom, closest to the source of heat. A vertical tube leads from this chamber to the top of the percolator. Just below the upper end of this tube is a perforated chamber.
The percolator is prepared for use by placing the desired quantity of water in the pot, and a corresponding amount of a fairly coarse grind of coffee in the top chamber. It is important that the water level should be below the bottom of the coffee chamber.
The basic coffee percolator is heated on a stove. The water temperature rises until the water in the bottom chamber boils, forcing some of it up the tube to the top where it splashes down onto the perforated lid of the coffee chamber. This water then seeps through the coffee grounds, out through the bottom of the coffee chamber, and drops back into the water in the bottom of the pot.
Meanwhile, colder water rushes into the bottom chamber. After a few seconds it again boils and the process is repeated. In this way liquid is continually dripping through the grounds until the temperature of the liquid (now brewed coffee) in the pot approaches (but has not yet reached) boiling point, at which stage the "perking" action stops and the coffee is ready for drinking. In a manual percolator it is most important to remove or reduce the heat at this point, as most coffee-drinkers agree that it should never be allowed to boil. As it is said, "Coffee boiled is coffee spoiled".
Some coffee percolators have built-in electric heating elements (and should of course never be used on a stove). Most but not all of these automatically reduce the heat at the end of the brewing phase, to then keep the coffee at drinking temperature without boiling it.
Coffee percolators once enjoyed great popularity, but percolated coffee has more recently been largely replaced by French press, drip brew and renewed interest in espresso. Percolators still maintain a following. The coffee has a distinctive flavour that some particularly appreciate.
