I. Experimental setup und test procedure Three coffee grinders from fully automatic household appliances were compared in a long-term test. For the test, a total quantity of 100 kg of coffee was ground per mill will the following mills: machine 1: conical grinding burr made of metalmachine 2: conical grinding burr made of metalmachine 3: flat grinding discs made of ceramics To determine the quality of the ground coffee during the course of the test, the following parameters were determined each after the grinding of 1, 5, 25, 50, 80 and 100 kg of coffee: grinding rateparticle size distributionextraction parameters of Espresso & Lungo (coffee brews were prepared on a seperate fully automatic coffee machine)extraction timebeverage weightcrema volumetotal dissolved solids (TDS)extraction yieldamount of titrable aciditysensory analysis II. Results grinding rate During the tests, the grinding rates of all mills have increased to the 10 kg mark. The grinding rate of the ceramic grinding mill, however, merely increased by about 10%, while the grinding rates of the metal grinders increased by 15-20%. Subsequently, the rates of the ceramic mill and the metal mill 1 again decreased approximately to the initial level, while the metal mill 2 retained the increase. On average over the entire test duration, the ceramic mill was clearly closest to the initially measured grinding speed (see Fig. 1). Since the quantity of coffee is controlled directly by the grinding time, this means that the ceramic mill maintains the initial quantity the most constantly. III. Results particle size distribution Regarding the particle size distribution, a difference in the range of fine particles is to be mentioned. The metal mill 1, produces a significantly higher percentage of fine particles over the entire test period than the ceramic mill, and the metal mill 2 has the lowest volume of fine particles at the highest coarseness setting (see Fig. 2). The ratio of mean particle size to fine particles is shown in Figure 3. If the share of fine particles is comparatively high, the beans are crushed more than cut, which means a...