Overview
ISO 11294:1994 specifies a routine gravimetric method for determining the moisture content of roasted ground coffee by measuring the loss in mass at 103 °C. The method is intended primarily for degassed roasted ground coffee because roasted coffee contains volatile matter (notably carbon dioxide) that can affect moisture determinations. Results obtained with ISO 11294 compare closely with moisture values from the Karl Fischer method (ISO 11817).
Key topics and requirements
- Scope: Routine determination of loss in mass at 103 °C for roasted ground coffee.
- Principle: Heat a weighed sample at 103 °C and calculate percent mass loss from pre- and post-drying weights (loss attributed mainly to water and other volatiles).
- Apparatus:
- Electric oven regulated to 103 °C ± 1 °C.
- Corrosion‑resistant metal or glass weighing capsule with cover (minimum useful area ~18 cm²; e.g., 50 mm diameter, depth 25–30 mm).
- Desiccator with effective drying agent.
- Analytical balance with precision to 0.1 mg.
- Sample size and preparation:
- Use a representative laboratory sample; mix thoroughly.
- Typical test portion: about 5 g in the prepared capsule.
- Procedure highlights:
- Dry empty capsule + cover 1 h at 103 °C, cool in desiccator, weigh.
- Add sample, weigh, then dry at 103 °C for 2 h ± 0.1 h.
- Cool in desiccator and weigh; compute percent loss as mass lost divided by initial sample mass × 100.
- Performance/fidelity:
- Interlaboratory studies (15 labs) show good agreement with Karl Fischer results.
- Repeatability: absolute difference between duplicate results in the same lab typically ≤ 0.1% (absolute).
- Reproducibility: absolute difference between labs typically ≤ 0.5% (absolute).
- Limitation: less suitable for coffees with very low moisture (~below 2%).
Applications and users
ISO 11294 is used for routine coffee quality control, specification testing and trade verification. Typical users include:
- Coffee roasters and processors performing in-house QC.
- Independent testing laboratories and inspection agencies.
- Commodity trading, import/export quality assessment.
- Research labs comparing gravimetric moisture with Karl Fischer determinations.
Use this method where a simple, standardized gravimetric moisture test is needed for roasted ground coffee and where volatile components (degassing) have been considered.
Related standards
- ISO 11817 - Roasted ground coffee: moisture by Karl Fischer method (reference/comparison).
- ISO 5725 - Precision of measurement methods (used for interlaboratory evaluation).
Keywords: ISO 11294, roasted ground coffee, moisture content, loss in mass at 103 °C, routine method, coffee testing, coffee quality control, Karl Fischer.
