A steam-driven unit operates by forcing water through the coffee by using steam or steam pressure. The first espresso machines were steam types, produced when a common boiler was piped to four group heads so that multiple types of coffee could be made at the same time. This design is still used today in lower-cost consumer machines, as it does not need to contain moving parts. Also, steam-driven machines do not produce as high of a pressure for extraction compared to pump-driven. This results in the crema, a hallmark of an espresso, being of lower quality.
If you're ready to pull the trigger on buying an espresso machine, be prepared to shell out a little cash. Espresso machines can be wildly expensive. Rightfully so. Pulling a perfect shot requires precision: the machine must maintain both precise temperature and stable pressure throughout the brewing process. Achieving this stability is difficult and requires complex machinery, which is why you can find machines for upwards of 6,000 dollars.
Water quality also plays a massive role in the way your coffee tastes. As we discovered in our review of the best water filters, water isn’t tasteless. Total dissolved solids (TDS) are what give “good tasting” water its sweetness — in fact, the SCAA recommends water with 150 milligrams per liter of TDS to brew coffee. (Want to check your water? A TDS reader is only about 15 bucks.)
Moka pots, also known as stove top espresso makers, are similar to espresso machines in that they brew under pressure and the resulting brew shares some similarities, but in other respects differ. As such, their characterization as "espresso" machines is at times contentious, but due to their use of pressure and steam for brewing, comparable to all espresso prior to the 1948 Gaggia, they are accepted within broader uses of the term, but distinguished from standard modern espresso machines.
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.