Coffee is prepared by the extraction of a complex array of organic molecules from the roasted bean, which has been ground into fine particulates. The extraction depends on temperature, water chemistry and also the accessible surface area of the coffee. Here we investigate whether variations in the production processes of single origin coffee beans affects the particle size distribution upon grinding. We find that the particle size distribution is independent of the bean origin and processing method. Furthermore, we elucidate the influence of bean temperature on particle size distribution, concluding that grinding cold results in a narrower particle size distribution, and reduced mean particle size. We anticipate these results will influence the production of coffee industrially, as well as contribute to how we store and use coffee daily.

Coffee extraction performed in an espresso machine is a process that depends on a delicate interplay between grind setting, coffee mass, water pressure and temperature, and beverage volume. Using a mathematical model based on the transport of solubles through a granular bed, paired with cafe-setting experiments, we elucidate the origin of inconsistencies in espresso production. Informed by the model, a protocol is proposed to systematically reduce coffee waste and beverage variation, resulting in highly reproducible shots.