An electric drip coffee maker can also be referred to as a dripolator. It normally works by admitting water from a cold water reservoir into a flexible hose in the base of the reservoir leading directly to a thin metal tube or heating chamber (usually, of aluminum), where a heating element surrounding the metal tube heats the water. The heated water moves through the machine using the thermosiphon principle. Thermally-induced pressure and the siphoning effect move the heated water through an insulated rubber or vinyl riser hose, into a spray head, and onto the ground coffee, which is contained in a brew basket mounted below the spray head. The coffee passes through a filter and drips down into the carafe. A one-way valve in the tubing prevents water from siphoning back into the reservoir. A thermostat attached to the heating element turns off the heating element as needed to prevent overheating the water in the metal tube (overheating would produce only steam in the supply hose), then turns back on when the water cools below a certain threshold. For a standard 10-12 cup drip coffeemaker, using a more powerful thermostatically-controlled heating element (in terms of wattage produced), can heat increased amounts of water more quickly using larger heating chambers, generally producing higher average water temperatures at the spray head over the entire brewing cycle. This process can be further improved by changing the aluminum construction of most heating chambers to a metal with superior heat transfer qualities, such as copper.

For many of us, the daily grind can't begin until we've had that first cup of piping hot coffee—so the right brewer is at the top of the list. The most basic coffee makers make at least a decent cup, but a little more money buys conveniences such as programmability, a thermal carafe to keep coffee hot longer, settings that let you adjust brew strength, and more.
“Strength, blend, decaf, cream, or sugar, there are many options when it comes to a cup of coffee. It seems every person has his or her own unique preferences to get them that perfect cup of joe. However, one factor that was often out of the home-coffee fan’s control was temperature. You either drank it at the temperature it came out of the coffee maker or you let it cool somewhat before sipping began. Cuisinart has aimed to turn that limitation on its head. This Cuisinart DCC-3650 adds a temperature control. It actually brews the coffee at one of three different user-defined temperatures. Impressive.”
‡Pre-Infusing: Pre-infusing is a technique where the dry coffee grounds are initially saturated with hot water, allowing a “bloom” of carbon dioxide to escape. This 45-second(ish) process puts hot water into contact with more surface area around each ground throughout the brewing process, as it’s no longer competing with the escaping gas bubbles. It can improve the quality of the final product, since this more uniform contact creates a more even extraction. It’s a feature that six of the 10 pots we tested incorporated into their designs — as well as all four of our top picks.
Bunn-O-Matic came out with a different drip-brew machine. In this type of coffeemaker, the machine uses a holding tank or boiler pre-filled with water. When the machine is turned on, all of the water in the holding tank is brought to near boiling point (approximately 200–207 °F or 93–97 °C) using a thermostatically-controlled heating element. When water is poured into a top-mounted tray, it descends into a funnel and tube which delivers the cold water to the bottom of the boiler. The less-dense hot water in the boiler is displaced out of the tank and into a tube leading to the spray head, where it drips into a brew basket containing the ground coffee. The pourover, water displacement method of coffeemaking tends to produce brewed coffee at a much faster rate than standard drip designs. Its primary disadvantage is increased electricity consumption in order to preheat the water in the boiler. Additionally, the water displacement method is most efficient when used to brew coffee at the machine's maximum or near-maximum capacity, as typically found in restaurant or office usage. In 1963, Bunn introduced the first automatic coffee brewer, which connected to a waterline for an automatic water feed.
Carafe style. Heavy coffee drinkers should look for a model with a thermal carafe. These coffee machines can keep your coffee warm for hours without having to sit on a burner, which can scald the liquid. Glass pots are not insulated and must sit on a heated burner to keep the coffee warm, so they’re an ideal choice for those who need only one or two cups a day. Some coffee drinkers insist that a glass carafe results in a better-tasting cup of joe. 
Our brew-performance tests measure the brew temperature and contact time (how long water stays within a sweet spot of 195° to 205° F for brewing). We measure concentration using a refractometer, a device that measures the amount of coffee dissolved in each brew. Our convenience tests look at how easy it is to set timers, fill the reservoir, clean the machine, and more. And for the first time, we’re incorporating predicted reliability and owner satisfaction ratings into the new Overall Score for each model. We determine these ratings for each drip coffee maker brand using survey data collected from thousands of CR members.
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