A "percolator" is a type of pot used to brew coffee, which functions by means of percolation. (The word itself is drawn from the Latin percōlāre, which means "to filter or trickle through.") This consists of the movement and filtering of fluids through porous materials.
Types of percolators
There are two basic types of coffee percolators.
The first type uses "pressure percolation," which forces boiling water under pressure through the grounds into a separate chamber. It is the type on which the espresso method is based.
The second type uses "gravity percolation," which consists of continually cycling the boiling brew through the grounds, using gravity, until the required strength is reached. This is the type used in many large-quantity coffee "urns."
Coffee percolators once enjoyed great popularity but were supplanted in the early 1970s by automatic drip coffee makers, and more recently by the French press, as well as a renewed interest in espresso coffee.
Percolators often expose the grounds to higher temperatures than other brewing methods, and may recirculate already brewed coffee through the beans. As a result, coffee brewed with a percolator is susceptible to over-extraction. In addition, percolation has the potential to destroy some of the volatile compounds in the beans. This results in a pleasant aroma during brewing, but a less flavorful cup. However, percolator enthusiasts praise the percolator's hotter, more 'robust' coffee, and maintain that the potential pitfalls of this brewing method can be eliminated by careful control of the brewing process.