The LS13 320 MW particle size analyser from Beckman Coulter was the instrument of choice in a study into the effect of bean origin and temperature on grinding roasted coffee.
Second only to oil, coffee is the most valuable legally traded commodity. It is prepared through 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. Researchers sought to discover whether variations in the production processes of single origin coffee beans affects the particle size distribution upon grinding.
For the study, it was assumed that the most important property of the ground coffee which can vary in the grinding process is the distribution of particle sizes. The first set of experiments explored whether the origin, type, or processing method of the bean had any effect on the particle size distribution, when ground under identical conditions. The second set of measurements explored if bean temperature at the time of grinding had any effect on produced particle size distribution.
The LS13 320 MW particle size analyser was chosen by researchers because it has a built in dark field reticule which is used to ensure correct optical alignment. An alignment check was carried out prior to every run to ensure the optimum accuracy of the particle size distribution. Particular care was taken to ensure correct optical alignment because ground coffee contains particles sizes spanning 3 orders of magnitude, including components larger than 100 μm, which can be challenging to measure with diffraction based techniques since they rely on distance measurements in reciprocal space.
Researchers concluded that particle size distribution is independent of the bean origin and processing method. But temperature definitely does matter - with cold grinding resulting in a narrower particle size distribution, and reduced mean particle size. The results of this study may have important ramification for both the coffee industry and for how coffee is stored and made at home.
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