Single dosing is the method of minimizing variability when grinding for espresso. The benefits of single dosing are: keeping beans fresh until use, being able to switch between coffees with less waste, and in some a lower height from hopper removal. But not all espresso grinders can single dose, and why are some better at this than others?
In traditional commercial espresso grinders the ground coffee passes through a horizontal chute before exiting into a doser or doserless chute. This layout has also been designed with weight of beans pressing down into the grinder. Some grinders have to be adjusted significantly finer when switching from a hopper full of beans to single dosing (which makes the grind process slower and potentially more clumpy), and even then the shot consistency and the quality of extraction may not be as good. Many home espresso enthusiasts fine tune their routine over time with dosing funnels, stirring the grounds for more even distribution, etc. Grind retention (coffee being left behind in the grinder) is also an increasingly common question, but the majority of the models mentioned in this article have low enough retention that it's not an issue. Baratza's grinders have the lowest grind retention among our lineup, but purging one to two grams of fresh beans through the other grinders in the morning should be sufficient to keep shots consistent.
Baratza: these grinders are extremely popular for single dosing, and they perform so well at it because they use a more vertical grinding path. If you adjust these grinders to their factory settings (5E for the Sette, 2K for the Vario and Forte AP), weigh 16-18 grams for a double spout portafilter or 20 grams for a bottomless portafilter, you should be close to pulling a good shot. Also, the all purpose nature of these grinders makes them one of the easiest to switch back and forth between different beans. With these models the grind setting for your favorite shot should be the same for single dosing as it is for using the grind timer.
Compak E5: the reason for the E5's success as a single doser lies in its colossal 650 watt motor. This motor power and torque does a great job of minimizing clumpiness and keeping the grinding process fast. The grind adjustment is also very simple.
Eureka Zenith 65E: this is one of our most popular grinders for cafes, but we've heard from home baristas who find the combination of the 500 watt motor, one-handed micrometric adjustment and adjustable chute can create great results.
Macap M7D: many fans of specialty coffee shops are flocking to the large conical grinders, and the M7D is quickly becoming one of the most popular because of its epic single dosing (as well as timed grinding) performance and 15" height with the hopper removed. The reason conical grinders perform so much better than traditional flat burr commercial grinders is partly due to the super low RPM (at 350-400RPM, these rotate at around 1/4 the speed of many flat burrs), and largely due to the size and shape of the massive conical burrs. In addition to exceptional cup performance, large conical grinders are the most consistent. Many users find they don't need to purge any coffee through and are able to go through a bag of coffee without adjusting the grind. The M7D is the shortest grinder in this class, and it also has a wide opening for beans. Its worm drive adjustment also makes it easy to precisely fine tune and switch between coffees.
Compak E10 and F10: Compak's reputation for elegant engineering has risen steadily in recent years, and their E10 and F10 grinders share the same basic specs as the M7D so they're also great single dosers. The functional differences between these models is how the grind is adjusted. These Compak and Macap conicals use the same functional size burrs and motors, so their grind speed and performance in the cup is comparable.