It's more of a challenge to choose among available coffee grinders than it is to actually grind coffee beans.
How We Tested
Coffee tastes best if the beans are ground fresh before they are brewed. With a wide variety of countertop coffee grinders on the market, it is no problem for home cooks to grind beans on demand. Most of the reasonably priced grinders, which generally cost around $20, employ propeller-type blades that work like a blender, literally chopping the beans as they spin. But our self-imposed price cap of $50 did allow us to include several low-end burr grinders (a fancier type of machine that works like a motorized pepper mill). We bought 10 popular models from seven manufacturers and 30 pounds of coffee beans. We tested each unit by grinding 2 ounces of coffee beans (about 8 tablespoons) and using those grounds to brew full, 40-ounce pots of coffee. Because most everyone we know uses an automatic drip machine, we did, too.
The first issue we addressed was the evenness of the grind. Blade grinders actually chop the beans with their furiously spinning blades. In a burr grinder, on the other hand, beans are truly ground a few at a time between two grooved disks, one stationary and the other rotating just above it. The grounds are fed out through a chute into a sealed container. The disks operate at roughly 7,000 to 9,000 revolutions per minute (RPM), while the motors in most blade grinders spin at 14,000 to 20,000 RPM.
We observed that the blade grinders’ rough treatment of the beans did often result in unevenly ground coffee, with particles ranging from dust to large chunks in the same batch, but we found we could improve the evenness of the blade grind either by grinding in short, quick bursts, with stops in between to shake the grinder to redistribute the grounds, or by shaking the grinder as it ground, much as you would a martini in a cocktail shaker.
The burr grinders produced a more even grind, but tasters didn’t find that more evenly ground coffee translated into improved flavor. Tasters did prefer the rich body of burr-ground coffee, but they also noticed the tendency of this coffee to taste slightly bitter, owing in part, no doubt, to the more fine and even grind, which made for the coffee’s greater exposure to and prolonged contact with the water in the coffee maker. These combined forces caused what coffee experts call overextraction, which occurs when too much flavor is extracted from the beans. In our tests, we were less likely to encounter this problem if the coffee was ground coarse, more so than even the coarsest setting on the burr grinders could accomplish.
We were surprised to discover that the coffee brewed with blade-ground beans was less likely to turn out bitter. The tasters did note that coffee from blade-ground beans had less body than coffee from burr-ground beans, but we were happy to sacrifice a little body for the reduced risk of brewing bitter coffee. We also learned that we could improve the body of the coffee somewhat by defying the blade grinders’ instructions and grinding the beans for a little longer, 20 to 25 seconds, rather than the recommended 10 to 15, without overheating the beans or jeopardizing smooth flavor in the coffee.
Overprocessing the beans into superfine coffee dust was another concern. Experts agree that the best grinders produce minimal dust, which can block waterflow through the filter in many coffee-brewing devices. None of the grinders we tested, however, produced enough dust to clog the filter.
The temperature of the coffee grounds was another factor we considered. Ideally, the beans should not heat up too much as they are ground because heat causes the evaporation of flavorful oils and results in a loss of flavor. Most experts claim that cheap blade grinders overheat the coffee beans. According to the infrared thermometer we used to measure the temperature of the grounds, this isn’t true. The burr grinders actually caused a greater increase in temperature, albeit a slight one. Our tasters, however, were not able to correlate a greater increase in temperature with poorer coffee flavor. The temperature increases we measured seemed to make very little difference.
We rated 10 coffee grinders, none priced higher than $50, and evaluated them according to the following criteria.
Number of tablespoons of coffee beans accommodated in the hopper.
Our most important test. Grinders with lids deep enough to accommodate all of the ground coffee without spills were preferred. Lids that were shallow or shaped to allow spills were downgraded. In addition, grinders with on-board cord storage were preferred, but this feature was not essential to earn a rating of good in this category. Design considerations for the burr grinders in the group were different. Since the hoppers on all of them accommodated the ground coffee amply, we judged them on the design of their on/off mechanism. We preferred a manual switch, with no automatic timer.
Grinders that could be cleaned with a few wipes of a damp cloth were preferred. Grinders with hard-to-reach crevices into which a brush had to be maneuvered for cleaning were downgraded.
The temperature of the coffee was measured three times immediately after grinding with an infrared thermometer (in degrees Fahrenheit). The results were then averaged to determine the average temperature increase for that mill. According to coffee industry experts, the lower the temperature increase, the better.