Continuous analysis of roasted coffee beans allows roasteries to improve their roasting settings, leading to higher energy efficiency and more consistent final products. Not only is flavor affected by the roasting degree, but caffeine content can also change. Conventional analytical methods such as HPLC (high-performance liquid chromatography) for caffeine concentration determination require technical skills to operate, chemical reagents, and take from several minutes to hours to obtain the results.

In contrast, near-infrared spectroscopy (NIRS) is a fast and chemical-free alternative for caffeine, water activity, and moisture analysis in roasted coffee beans and ground coffee. The NIRS solution is easy to use and does not require any sample preparation. These analyzers can be operated nearby the roaster or in a quality control lab.

Up to 35 roasted ground coffee bean samples were analyzed on a Metrohm DS2500 Solid Analyzer with the DS2500 Holder and NIRS mini sample cups (Figure 1). Samples were positioned into the NIRS mini sample cups for the analysis in diffuse reflection mode. Data acquisition and prediction model development were performed with the software package Vision Air Complete (Table 1).

Reference values for caffeine, water activity, and moisture were obtained with the respective primary methods. Caffeine analysis followed the ISO 20481 guideline and was conducted with an ion chromatograph (IC), water activity determination followed the ISO 18787 norm, and moisture determination was performed according to DIN 10772-1.