AN-NIR-104
2023-04
Analysis of green coffee beans by near-infrared spectroscopy
Reliable density, water activity, and moisture results in seconds
Summary
Before they are made suitable for consumption, raw (green) coffee beans must be roasted. For roasters, the continuous analysis of green coffee beans allows the improvement of warehouse management. This information helps roasters prioritize the order of lots to process and to optimize roasting settings for more consistency and energy efficiency. However, the time, effort, and somewhat complex workflows required when using traditional analytical methods (e.g., densimeters, water activity analyzers) can be an inconvenience.
Near-infrared spectroscopy (NIRS) is a fast, multiparameter analytical method suitable for the analysis of density, water activity, and moisture content of green coffee beans. Neither chemicals nor sample preparation are required, making NIRS easy to use in the warehouse, nearby the roaster, or in a quality control laboratory.
Experimental equipment
Up to 31 samples of green coffee beans were analyzed on a Metrohm DS2500 Solid Analyzer with the DS2500 Holder and NIRS mini sample cups (Figure 1). Green coffee beans 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 density, water activity, and moisture content were obtained with the respective primary methods. Water activity analysis followed the guideline of ISO 18787, moisture content was determined according to ISO 6673, and density was determined with a density determination set for a Precisa balance.
Table 1. Hardware and software equipment overview.
Equipment | Article number |
---|---|
DS2500 Solid Analyzer | 2.922.0010 |
DS2500 Holder | 6.7430.040 |
NIRS mini sample cups | 6.7402.030 |
Vision Air 2.0 Complete | 6.6072.208 |
Result
The obtained Vis-NIR spectra (Figure 2) were used to create prediction models for the different reference parameters. To verify the quality of the prediction models, the data sets for water activity and moisture were split into calibration and validation sets. A leave one out validation procedure was used for density. Correlation diagrams which display the relation between the Vis-NIR prediction and the reference values are shown in Figures 3–5 together with the respective figures of merit (FOM).
Result density in green coffee beans
Result water activity in green coffee beans
Result moisture in green coffee beans
Conclusion
This Application Note shows the feasibility of near-infrared spectroscopy for the analysis of density, water activity, and moisture content in green coffee beans. Without using any chemicals, these quality parameters can be measured with results obtained in less than a minute. This easy-to-use method allows roasters to improve warehouse management by selecting raw beans to roast based on indicators of shelf life. Additionally, roast settings can be optimized for better product consistency and higher energy efficiency.
Internal reference: AW NIR CH-0068-042023