Strength of coffee beans under static and dynamic loading

Abstract

NEDOMOVÁ ŠÁRKA, TRNKA JAN, STOKLASOVÁ PAVLA, BUCHAR JAROSLAV: Strength of coff ee beans under static and dynamic loading. Acta Universitatis Agriculturae et Silviculturae Mendelianae Brunensis, 2013, LXI, No. 3, pp. 743-749 Paper deals with experimental research on the crushing of coff ee beans of diff erent kinds under quasi-static and dynamic compression. The process of the crushing is described in details. It has been shown that there is variability in the crushing strength values. A relation between crushing strength and the coff ee grain shape is also studied. Roasted Arabica coff ee (Coff ea arabica) beans were used for analyses. Arabica coff ees were produced in diff erent countries. All Arabica samples were submitted to a light roast. The detail analysis of the experimental data shows that there is no signifi cant relation between parameters describing the fracture behaviour of the grains and grain geometry. These parameters are also independent on the grain weight. Compression of the coff ee grains leads to their crushing. The fracture force is diff erent for the diff erent kinds of the coff ee. The same is fact valid also for the strain at the fracture and for the energy absorbed during the grain crushing. Dynamic loading leads to the increase in the fracture force of coff ee grains in comparison with the quasi static loading. coff ee beans, compression loading, strength, impact loadingThe knowledge of the strength and toughness of the coff ee beans is necessary in order to evaluate their brittleness. The reaching of a certain degree of brittleness is very important for the grinding to which coff ee beans have to be subjected to before brewing. The uniformity of the product of the grinding process depends on various factors including the brittleness of the roasted coff ee bean and it aff ects the extraction of soluble solids to obtain the coff ee brew (Clo and Voilley, 1983;Clarke and Macrae, 1987). Even though the changes in the textural and mechanical characteristics to which the coff ee bean undergo during roasting play a relevant role in the quality of the roasted beans, these properties have been scarcely studied until now.The textural changes of coff ee beans during their roasting have been studied e.g. by Pitia et al. (2001) using of the static compression of the coff ee beans. The same technique has been used for the study of the infl uence of the moisture content and water activity on the mechanical properties of the coff ee beans (Pitia et al., 2007). This technique has been also used for the study of mechanical properties of many others beans, see e.g. (Tran et al., 1981, Borges andPeleg, 1997; Al Salah and Galland, 1985). In our previous paper (Nedomova, 2010) results on the coff ee grain compression has been presented. These results have been obtained for the quasi static loading.The grinding of the coff ee represents a loading process which is dynamic rather than static. It means the mechanical properties like crushing strength should be evaluated at the dynamic loading. In ...

Physical and Mechanical Properties of Coffee Cherries and Beans in Africa: Review and the State of Arts

“…The analyses of Arabica coffee roasted experimentally had described the fracture behaviour of the grains and given geometry. However, [40] was confused about the number of beans used to calculate the mean value where 1000-beans were reported in previous work [34]. But the two researchers got the same results on the physical characteristics of coffee selected in 20 regions.…”

“…The grater sleeve of drum pulper, disc pulper contains bulbs that separate pulps and beans and help the beans to slide in pulping clearance toward the outlet of machine. Therefore, according to [40] the analysis showed that the crushing strength of a single bean under static force applied perpendicularly to the flat surface of Arabica coffee beans from Ethiopia, Kenya and Tanzania varies in between 30N and 60N and the correlated dynamic force can rise up 75N. The corresponding displacement is about 0.3mm.…”

“…The description was limited to numeral simulation of coffee grain mechanical behaviour that can be supported by the derived formulas that are also describing the grain contour and sphericity. According to [40], the investigation was conducted using the same data, but with a sample of 20 beans selected randomly (while in previous was 100 beans). The analyses of Arabica coffee roasted experimentally had described the fracture behaviour of the grains and given geometry.…”

Changes of Mechanical Properties and Color from Arabica Coffee Cherry to Green Bean

“…The mechanical properties and color of agricultural crop play an essential role in providing engineering properties of the coffee bean. Some researchers [17][18][19][20] had conducted the study on mechanical properties and color of green bean coffee. Results of research stated that mechanical properties and color could be used for the design of harvesting and classification systems, as well as for a rapid determination of coffee quality [17].…”

“…Results of research stated that mechanical properties and color could be used for the design of harvesting and classification systems, as well as for a rapid determination of coffee quality [17]. The fracture force is different for the different kinds of coffee [18]. Some engineering properties varied among the beans from different colors of coffee cherries [19] and post-harvest processing factors were found to influence the physical and sensory quality of green coffee beans [20].…”