Overview
ISO 9727-3:2007 - Cylindrical cork stoppers - Physical tests - Part 3: Determination of humidity content - specifies standardized methods to measure the moisture (humidity) content of ready-for-use or semi-worked cylindrical cork stoppers. The standard defines both a gravimetric (oven-drying) “long method” and an electrical resistivity-based “rapid method,” including environmental conditions, equipment, measurement steps, and how to calculate and report results.
Key topics and requirements
- Two test methods
- Long (gravimetric) method: oven-dry to constant mass and calculate moisture as percentage mass loss.
- Rapid method: resistivity measurement using a two‑electrode sensor calibrated with a standard resistor.
- Equipment and settings
- Balance with resolution ≤ 0.001 g.
- Ventilated drying oven regulated at 103 °C ± 4 °C.
- Desiccator with hygroscopic salt and saturation indicator.
- Resistivity meter with cork‑compatible two‑electrode probe and reference resistor.
- Procedure highlights
- Long method: weigh each stopper, dry (initially 24 h at 103 °C ± 4 °C), transfer to desiccator, reweigh, and repeat drying cycles until mass change between successive weighings is ≤ 10 mg (“constant mass”).
- Rapid method: insert electrodes 4–6 mm into the stopper, perpendicular to grain for natural cork; read displayed moisture or convert resistivity via device calibration curve.
- Test conditions
- Ambient test room: 21 °C ± 4 °C and relative humidity 60 % ± 20 %.
- For the rapid method, ensure sample temperature is 21 °C ± 4 °C at test start.
- Results and reporting
- Long-method results rounded to 0.1%; rapid-method values rounded to the nearest percent (rules provided).
- Final result = arithmetic mean of sample results, with standard deviation, maximum and minimum (rounded to 0.1%).
- Test report must state which method was used, sample ID, sampling report, results and any deviations from the standard.
Applications and users
- Quality control laboratories in cork manufacturing and finishing.
- Cork producers and suppliers verifying moisture for production control.
- Winery procurement and bottling operations assessing stopper condition for sealing performance.
- Independent testing laboratories and compliance auditors.
- Researchers studying cork physical properties and storage behavior.
Practical benefits include ensuring consistent stopper performance, optimizing storage/conditioning, and minimizing failures related to inappropriate moisture levels.
Related standards
- ISO 9727 series (Physical tests for cylindrical cork stoppers): Part 1 (dimensions), Part 2 (mass and apparent density), Part 4 (dimensional recovery after compression), Part 5 (extraction force), Part 6 (liquid tightness), Part 7 (dust quantity).
- ISO 633 (Cork vocabulary) referenced for terms and definitions.
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