Peek inside your manual or electric grinder and you’ll see cone-shaped burrs – this is the bit that does the grinding. But you may also have heard of flat burrs. What’s the difference between these coffee grinders and should you care?
These grinders use an outer serrated burr and an inner cone-shaped burr (hence the name). When the inner burr spins, the sharp edges pull beans into the gap between the burrs where they’re ground into smaller and smaller pieces.
The conical shape allows for uniform grinding and a high level of grind size control. It also allows for grinding at a lower speed – meaning less noise and heat.
Conical burrs produce coffee grounds in two distinct particle sizes, although you’d need a microscope to spot this. This doesn’t matter so much if you’re brewing a filter or pourover, but if you’re making espresso it can make all the difference. The smaller grounds restrict the flow of water in an espresso portafilter meaning the larger grounds have more time to extract flavour. By the time the larger grounds have experienced a balanced extraction, the smaller grounds have over-extracted, adding bitterness to the final cup with a heavy, sometimes creamy or silky, body. This is typical espresso coffee.
Flat burrs are like two, small, squished doughnuts with razor-sharp edges. They face each other, and when beans are ground they are forced through from the inner teeth to the outside of the burrs. The beans spend more time in contact with the burrs, producing more heat but also a more precise grind. It needs a stronger motor, which produces the loud, high-pitched whine you’ll recognise from larger grinders in cafes.
For home use, the extra cost, size and noise often means a flat burr grinder isn’t an option. But you can taste the difference. Higher precision and uniformity mean a skilled barista can pull a broader range of espresso shots from a typical thick, almost gritty shot to a long, bright, sweeter shot.
There are lots of factors that’ll help you make the perfect cuppa. Looking to experiment and produce speciality, cafe-standard espresso? A flat burr grinder may be the best choice. If not, conical burrs will be just fine. Find out more in our best grinder feature.
If you liked our coffee grinders comparison, find more brewing-related features here.