Overview
ISO 8784-3:2022 specifies a laboratory method for the microbiological examination of dry market pulp, paper and paperboard - specifically the enumeration of yeast and mould based on disintegration. The standard describes a pour-plate procedure that converts a disintegrated fibre sample into a 1% suspension, plates it on a specified culture medium, incubates the plates, and reports results as colony-forming units (CFU) per gram.
Key topics and technical requirements
- Scope: Total number of yeast and mould CFU in dry pulp, paper and paperboard after disintegration.
- Principle: Pour plate method using a fibre suspension; colonies developing in agar are counted after incubation.
- Sample preparation:
- Cut representative sheets (sampling per ISO 186 / ISO 7213) and remove surface-contaminated layers.
- Prepare a 1% fibre suspension (e.g., 2 g sample + 200 ml diluent).
- Disintegrate until free of fibre clumps; avoid suspension temperature > 45 °C.
- Culture media:
- Sabouraud dextrose chloramphenicol agar (SDCA) specified (e.g., dextrose 40 g, peptic digest 5 g, chloramphenicol 0.05 g, agar 15 g per litre).
- Media preparation and quality guidance referenced to ISO 11133.
- Diluents and additives:
- Quarter-strength Ringer’s solution (composition provided).
- Optional non-ionic surfactant (Tween 80) recommended to aid cell release (20 µl per litre).
- Apparatus:
- Sterile disintegrator or equivalent homogenizer, incubator at 25 ± 1 °C, sterile glassware or disposable alternatives, wide-mouth pipettes, colony-counting device.
- Incubation and enumeration:
- Incubate plates at 25 °C ± 1 °C for 5 days.
- Count yeast and mould colonies and calculate CFU per gram (reporting on dry-mass or as-received basis).
- Reporting: Includes test conditions, media used, diluents, disintegration method, and calculated CFU/g.
Applications and users
- Who uses it: Microbiology and quality-control laboratories in the pulp and paper industry, third-party testing labs, regulatory authorities, and R&D teams assessing product hygiene or storage stability.
- Practical uses:
- Routine quality monitoring of paper, paperboard and dry market pulp.
- Investigations of biological contamination, product shelf-life issues, and process hygiene.
- Supporting supplier specifications and compliance testing for pulp and paper materials.
Related standards
Keywords: ISO 8784-3:2022, yeast and mould enumeration, pulp paper board microbiological test, disintegration method, CFU per gram, Sabouraud dextrose chloramphenicol agar, Ringer’s solution, Tween 80.