The drip brew method generally consists of pouring 195°F to 205°F (90.6°C to 96.1°C) water through a bed of coffee grounds held in a filter basket or cone. The water flows through the grounds continuously during the brew cycle, forced only by gravity. Quite a few brewing devices are built around this method, from simple one-cup mug-top filter cones, to feature-packed electric automatic kitchen counter top appliances with digital timers and integrated grinders.
Filter brewed coffee is usually passed through a paper filter. This has a significant effect on flavor. Some flavor components will not pass through the filter as readily as others. Paper filters also do a good job of holding back the smallest particles in coffee grounds - the dust. These factors make for a cleaner, brighter flavor, or, as advocates of other brew methods might argue, they rob the brew of some of its richness.
Paper filters can impart an undesirable flavor to the coffee that passes through them. To minimize this effect, we recommend using only oxygen bleached white filters. The brown, unbleached filters that have come into the market, in response to concerns about chlorine bleached white filters, are likely to impart more off flavors than their bleached counterparts. Oxygen bleached filters address concerns about the chlorine bleaching process without compromising coffee quality.
Some drip systems use "permanent" metal filters. These filters do not capture or impart flavors as paper filters do, and coffee dust is more likely to pass through them to form sediment in the brew. Some people will appreciate the effect a metal filter has on flavor characteristics, while others will simply use a metal filter to avoid having to purchase and dispose of paper filters.
The drip brewing method is a bit more complex than the steeping method, and more difficult to control. So why is the drip method so popular? I would speculate that it is simpler to optimize a drip brewing system for convenient brewing preparation and cleanup than it would be to optimize a system based on the infusion method. Also, drip brewed coffee often has flavor characteristics that differ noticeably from infusion brewed coffee. This may be the result of differences in the brewing dynamics and chemistry of the two methods, or the the mechanical differences in brewing devices, such as filter type and performance.
Conceptually, steeping is the simplest way to brew coffee: Mix hot water with coffee grounds and, after a few minutes, separate the rich brown brew from the grounds. The press pot, or French press, is the most popular brewing device based on the steeping method.
The characteristic flavor of steeped coffee is similar to that of drip coffee, but may be richer when metal filters or screens are used to separate the coffee from the grounds. The molecular dynamics of the extraction process may be different since extracted compounds remain in close proximity to the coffee grounds and increase in concentration as the brew cycle progresses, while in the drip method, water is constantly carrying the extracted compounds away from the grounds. Infused coffee stews in it's own juices. Whether this produces unique characteristics is speculation on my part. Perhaps the coffee chemists will investigate this for us, if they haven't already.
Infusion brewing seems simple, but manual infusion devices, such as the press pot, demand that the user control the brew time. The designs of drip brew systems allow users to ignore brew time, as long as the grind and coffee-to-water ratio are within proper bounds. Brew time has been designed into the drip system. So while infusion brewing is simple to think about, it is often more complex, or at least less convenient, in daily practice.
Automatic infusion brewers are feasible. Capresso offered an automatic infusion brewer at one time. But the drip systems remain dominant. If you have ever used a press pot, you know that brewing and cleanup can be slightly more complicated and messy than for a drip system. You must time your brew to control the level of extraction, and when you are finished, the coffee grounds must be cleaned out from the bottom of the vessel. With most drip systems, you simply pour the water, or flip a switch, and wait for the process to finish. The paper filter conveniently packages the grounds for disposal. The infusion method of brewing is most often practiced by individuals who appreciate the manual process and the rich characteristic brew of a French press.
The espresso brewing method involves the most extensive list of specifications. There are the brewing equipment and process specifications: 22 to 28 second brew time, 88-95°C water, 9 to 10 atmospheres pressure in the brew chamber, 23.5mL:7g to 31.3mL:8.5g water:coffee ratio per serving, and finely ground coffee, adjusted to achieve proper brew time. There are specifications about the degree of roast, and the proper blend of beans from widespread origins and different species of coffee trees. There are practical and fanciful rituals performed by espresso machine operators to prepare the ground coffee before brewing. Finally, there are well defined ways to present and consume the beverage after it has been prepared. Espresso has exacting brewing specifications, a rich tradition, and an enthusiastic following. It might be said to represent the highest development of coffee culture.
With all its fame, history, and exacting standards, espresso is perhaps the most often botched coffee drink in the United States. It takes training, practice, and a certain amount of passion to use a commercial espresso machine properly. These factors are too often absent, especially in non-café settings. Often managers and owners of establishments that serve espresso lack the training and passion required to ensure that employees know how to produce a quality beverage. There is the misconception that the machine takes care of everything. Espresso machine operators that don't know what good espresso looks or tastes like will still be able to pump out ounces of foul black water that can be passed off as espresso to unwitting customers. But the machine is a tool that needs care and finessing. Without proper care and understanding on the part of the operator it will not yield true espresso.
The unique characteristics of properly brewed espresso are its fresh aroma, similar to ground coffee, its natural sweetness, an effervescence on the tongue, and its lingering pleasant and aromatic aftertaste. Bitterness is not one of the primary, defining characteristics! Good espresso is delicious without any added sweeteners or milk. This can hardly be said for what passes as espresso in many people's minds. The crema on top of the espresso should be smooth and thick - thicker than a film - and it should be a yellowish brown or reddish brown, depending on the the coffee blend used.
Gasses and oils dissolved under high pressure form the characteristic espresso crema when the liquid emerges from the filter spouts. This stream of foamy liquid is said to pour like warm honey. It is claimed that as the foam and liquid separate in the cup, the crema serves as a seal to keep volatile flavor components in the brew from escaping.
Home espresso machines generally approximate good espresso. Some home units produce excellent results, and it appears more high quality home units are becoming available. The home models at the lower end of the price spectrum are less likely to produce or maintain enough heat and pressure to brew espresso properly, although some of the higher-priced models may suffer from the same problems. Home espresso machines should be purchased from knowledgeable purveyors and tested before purchase. If you shop for an espresso machine like you would shop for a toaster you are likely to get home brewed espresso that tastes like burnt toast.
Coffee should never be boiled. To some, that statement amounts to a universal law, but in an overview of brewing methods we should acknowledge popular exceptions to and transgressions of this law. Percolators used to be the most popular devices for brewing coffee in the United States. Percolators force the same overheated water through the same coffee grounds continuously throughout the brew cycle. From our perspective, a percolator seems designed to rob good coffee of its flavor potential (to put it mildly), but some people have developed a taste for percolated coffee, and prefer it to coffee prepared any other way.
Occasionally we hear of "cowboy coffee", or coffee simmered in a pot of water on a stove top or over a campfire. (I first came across a description of this method in chapter 24 of Jack Kerouac's The Dharma Bums, where he refers to it as "french style".) This is the steeping brewing method in water that is too hot, with little regard for an exact coffee mass to water ratio. Still, it's bound to produce a wonderful aroma and a strong beverage that may be enjoyable in certain circumstances.
Many people are familiar with Turkish coffee, a brew prepared from very finely ground coffee, sugar and sometimes cardamon, in a long-handled metal cup. The cup is held or placed over a flame until the brew just boils, and then it is removed for a moment to cool. The brew is then brought to a boil and cooled one or two more times. Turkish coffee preparation is a distinct art and tradition, perhaps comparable to the tradition of espresso.