†Programmable Brew Time: Conventional wisdom frowns at grinding beans early and programming a pot to brew later. The aromatic compounds in coffee beans start to oxidize as quickly as 15 minutes after grinding, which causes coffee to start losing aroma and flavor. But Michael Ebert, senior consultant at Firedancer Coffee Consultants, LLC, assured us that, given the trade-offs for convenience, “grinding the night before will still make a great coffee — just not as great as it could be.” Seven of the 10 pots we tested are programmable, including three of our top picks (all but the Bonavita).
Some machines use a single boiler kept at steaming temperature, but water for brewing is passed through a heat exchanger, taking some heat from the steam without rising to the same temperature. Although the water for brewing remains at a lower range than that required for steaming milk, it is still too hot for proper coffee extraction without first cooling; thus this type of machine requires a cooling flush of 4–6 seconds prior to the first espresso pull. Once the machine is dialed into the proper temperature, as many shots can be pulled as required without refreshing. However, if the user leaves the machine idle again for some period, the flushing process will need to be repeated. The HX variety is found in many mid-range machines and many users install thermometers to assist them is dialing in correct temperatures. There is some controversy as to the temperature stability of the brewing water, since it is indirectly converted from steaming temperature to brewing temperature, rather than kept at a brewing temperature.
Other coffee brewing devices became popular throughout the nineteenth century, including various machines using the vacuum principle. The Napier Vacuum Machine, invented in 1840, was an early example of this type. While generally too complex for everyday use, vacuum devices were prized for producing a clear brew, and were popular up until the middle of the twentieth century.
It can take a little while to get to know the ins and outs of a new coffee maker. In CR’s labs, each drip coffee maker we test brews roughly 65 cups by the time our engineers are through with it. And brewing is just one of many aspects we look at. We test for handling and convenience, too, so you can choose a model that helps you sail through morning madness.