Overview
ISO 7513:1990 defines a laboratory method for determining the moisture content of instant tea in solid form by measuring the loss in mass when a test portion is heated in air at 103 °C. The method treats the mass lost under the specified conditions as moisture (minor contributions from other volatiles are considered negligible for practical purposes). The procedure supports quality control, product specification and regulatory compliance in food testing laboratories.
Key Topics
- Principle: Heat a test portion in a controlled oven at 103 °C and determine the loss in mass after drying.
- Apparatus: Constant-temperature, fan-assisted oven (103 °C ± 2 °C); weighing bottle or dish with close-fitting lid (aluminium or glass, ~70 mm diameter × 20 mm height); desiccator with efficient desiccant; analytical balance readable to 0.001 g.
- Test portion: About 4 g of prepared sample weighed to 0.001 g.
- Drying conditions: 2 hours at 103 °C ± 2 °C with the lid removed; cool in desiccator for at least 30 minutes before weighing.
- Number of determinations: Perform two determinations on the same test sample and report the arithmetic mean if repeatability requirements are met.
- Calculation: Moisture content (%) = ((m1 - m2) × 100) / m1, where m1 is the initial mass of the test portion and m2 is the mass after drying.
- Precision: For moisture contents in the range 3% to 4% (m/m): repeatability (same operator, same apparatus) difference ≤ 0.2% absolute; reproducibility (different laboratories) difference ≤ 0.8% absolute.
Applications
- Quality control: Routine monitoring of moisture content in instant tea batches to ensure consistency and conformance to product specifications.
- Stability and shelf-life assessment: Moisture data inform packaging and storage decisions to maintain product stability and prevent caking or microbial growth.
- Laboratory compliance: Provides a standardized oven-drying reference method for inter-laboratory comparisons and regulatory reporting.
- Production troubleshooting: Identifies deviations in drying or production processes that affect final moisture.
Related Standards
- ISO 7516:1984 - Instant tea in solid form - Sampling. Sampling shall be carried out in accordance with ISO 7516 as referenced in ISO 7513:1990.
Test reports prepared using ISO 7513:1990 should specify the method version, all operating details not covered in the standard (for example oven model or deviations), and any incidents that could have influenced the result. This ensures traceability and supports reliable interpretation of moisture determinations.
Open preview (PDF)Instant tea in solid form — Determination of moisture content (loss in mass at 103 degrees C)
