Overview
ISO 24115:2012 - "Green coffee - Procedure for calibration of moisture meters - Routine method" describes a standardized routine for adjusting and calibrating moisture meters used on green coffee beans. The standard defines how to prepare and use reference samples (RSs) - green coffee beans with oven-determined moisture contents (per ISO 6673) - to assign moisture values and calibrate instruments, including direct- and indirect-reading devices. It applies specifically to green coffee as beans.
Key topics and technical requirements
- Reference samples (RSs): Prepare a minimum of n ≥ 5 RSs with moisture mass fractions spanning about 8.5% to 13.5%; differences between consecutive RSs typically 0.7–1.3 percentage points. RS preparation and oven moisture determination are specified in Annex A and ISO 6673.
- Equipment: Moisture meter (with a green coffee channel), thermometer (0–120 °C, 0.1 °C divisions) if instrument does not auto-display temperature, balance readable to 0.1 g, and equipment required for ISO 6673.
- Test conditions: Perform calibrations at ambient temperature and 40%–70% relative humidity; condition RSs to ambient temperature before testing.
- Procedure highlights:
- Align instrument bias using differences between RS oven values and meter readings.
- For each RS, take at least three replicate readings and compute means and experimental standard deviations.
- For indirect-read devices, generate a calibration curve (readings vs. oven moisture) and apply appropriate regression (linear in most cases).
- Temperature correction: Determine correction due to bean temperature (or use manufacturer’s auto‑correction); quantify as a slope ξ (Δreading/ΔT) and apply C_T.
- Uncertainty evaluation: Follow ISO/IEC Guide 98-3 approach. Components include RS value uncertainty, repeatability (s/√j), instrument accuracy, resolution, and temperature effects. Report expanded uncertainty (typically k = 2, ≈95% confidence).
- Reporting: Express sample moisture as meter reading plus instrument and temperature corrections ± expanded uncertainty.
Practical applications - who uses ISO 24115:2012
- Coffee quality laboratories and third‑party calibration labs performing routine calibration of moisture meters.
- Coffee exporters, importers, green bean warehouses, and roasters needing reliable moisture measurements for quality control, storage decisions, and commercial transactions.
- Moisture meter manufacturers and calibration services validating instrument performance and producing calibration curves for green coffee channels.
- QA managers implementing standardized measurement and reporting practices for green coffee moisture content.
Related standards
- ISO 6673:2003 - Green coffee: Determination of loss in mass at 105 °C (oven reference method)
- ISO 3509 - Coffee and coffee products - Vocabulary
- ISO/IEC Guide 99 (VIM) - Metrology vocabulary
- ISO/IEC Guide 98-3:2008 - Uncertainty of measurement (GUM)
Keywords: ISO 24115:2012, green coffee, moisture meters, calibration, reference samples, ISO 6673, calibration curve, uncertainty, temperature correction.
