What's the difference between flat burrs and conical burrs?
Flat grinding burrs produce thin slices of ground coffee and are very effective in terms of extraction yield. Flat burr grinders have two identical and parallel rings that are serrated on the side that faces the other. Conical grinding burrs produce flakes of ground coffee and can extract all of the aromas from the beans which grants an extra special texture. Conical burr grinders have two cone-shaped burrs with ridges that grind and crush the coffee.
From an output perspective, flat grinding burrs dispense in-between the two burrs and crush the coffee beans into a uniform size. Therefore, they need speed (more than 700 rpm) to function properly. Conical grinding burrs dispense coffee by gravity so the motor speed is lower. Conical burr grinders function at the lowest possible speed while maintaining high output and the best consistency. Slower speeds also help to keep the grinding cool so as not to affect the roast. Both types of burr grinders have one stationary burr while the motor turns the other. Also, both types of grinders are known for their flexibility and quality. Flat burrs generally wear quicker, but are less expensive to replace. Conversely, conical burrs tend to last longer but are more costly to replace.
Photo credit courtesy of The Coffee Technicians Guild.