Difference between flat and conical burrs?

Conical burrs produce a bimodal grind with more fines, delivering body and sweetness — a flattering profile for espresso. Flat burrs produce a more unimodal, cleaner, more legible grind — the preferred profile for filter. It isn't a question of 'better', but of different sensory signatures.

Conical burrs pair a fixed central male cone with a rotating female cone around it. Coffee drops vertically by gravity between the two and is ground on the way down. This geometry has two measurable consequences. First, the particle-size distribution is naturally bimodal: two distinct peaks, one around 200-300 µm (fines and small fragments) and another around 500-700 µm (the espresso core). That bimodality, observed via laser diffraction in work by Mathieu Theis (Eureka) and replicated in other labs since 2018, builds a puck that restricts flow and emphasises body and sweetness — the classic Italian espresso signature.

Flat burrs are two parallel discs, one fixed and one rotating, whose faces are machined with concentric cutting patterns. Coffee enters at the centre through a feeder screw, is pulled outward by centrifugal force, and is ground along the peripheral cutting zone. The resulting distribution is more unimodal, with a narrower peak and fewer fines. In the cup that translates into more aromatic clarity, sharper separation of notes (floral, fruity, spicy), a less enveloping body — characteristics prized in V60, Chemex or very light third-wave espresso.

Three secondary parameters matter beyond geometry: diameter, rotation speed, and cutting temperature. Flats tend to be larger (64-98 mm) because their cutting surface is annular and must offset the shallower chamber height; conicals can stay compact (40-58 mm) and remain efficient. Flats generate more heat at high rpm — high-end models therefore run at 400-800 rpm to preserve volatile aromatics. Conicals often spin at 1,400 rpm without significant thermal issues.

At the World Barista Championship, both geometries have won: since 2015, finalists alternately pick EK43-style flats for filter and either conicals or espresso-dedicated flats for the espresso category. The Belgian scene mirrors that split: most specialty roasters in Brussels, Ghent, Antwerp and Liège keep a filter grinder with flat burrs (EK43-class) and a separate espresso grinder (conical or espresso flat) in the shop — never a single all-purpose unit. For a home enthusiast, the rule of thumb is simple: if 80 % of your coffees are espresso, go conical; if 80 % are filter, go flat.

Flat vs conical burrs — signature