Overview
ISO 3631:2019 - Citrus fruits: Guidelines for storage provides internationally agreed recommendations for storing major groups of citrus fruits, with or without refrigeration, in stores and transport equipment (containers, trucks, railway cars, ships). Covered species include oranges (Citrus sinensis), mandarins (C. reticulata), lemons (C. limon), grapefruits (C. paradisi) and limes (C. aurantifolia, C. latifolia). Annexes list cultivars, principal commercial varieties and common storage damage.
Key topics and technical requirements
- Scope and fruit groups: Guidance separated by species and cultivar because storage behaviour varies by type and region.
- Harvesting criteria: Fruits must be harvested fit for consumption; fallen (ground) fruit should not be harvested. Maturity indicators include juice content, flavour and TSS/TA ratios (refer to ISO 2173 / ISO 750 for measurements).
- Post-harvest handling:
- Sorting to remove damaged or infected fruit; washing, rinsing and brushing recommended (lemons/limes sometimes not washed).
- Fungicidal treatments applied promptly after harvest; heat dips (35–48 °C for 1.5–5 min) may be used for Phytophthora control.
- Wax coatings (e.g., carnauba, paraffin) can be applied after washing; permitted amounts noted (up to 140 mg/kg is an example given).
- Ethylene degreening is discouraged for fruit intended for long storage.
- Packing and storage preparation: Fruit may be stored loose or wrapped (tissue or fungicide-impregnated substrates). Careful packing prevents movement without causing bruising.
- Storage conditions:
- Non-refrigerated: typically 10–18 °C in well-ventilated premises.
- Refrigerated: includes pre-cooling (final temperature reached in 3–4 days) and controlled storage.
- Typical environmental controls: relative humidity 85–95%, air-circulation ratios (pre-cooling 100–200; storage 25–50), fresh air exchange once or twice per hour to avoid CO2 accumulation (~0.2–1.0%).
- Temperature limits depend on species, variety and intended storage duration (examples: grapefruit short-term at 9–10 °C; some varieties tolerate brief 0 °C treatments for pest control).
- Keeping life: Depends on variety, harvest timing, growing conditions and handling.
Applications and users
ISO 3631 is practical for:
- Citrus growers and orchard managers (harvest timing, pre-storage handling)
- Packing houses and post-harvest processors (washing, fungicide/wax application, grading)
- Cold chain operators, refrigerated storage facilities and transport companies
- Quality assurance teams, food safety auditors and regulators
- Exporters/importers needing consistent storage practices and reference to cultivar-specific guidance
Related standards
- ISO 2169 (measurement of physical quantities affecting storage)
- ISO 2173, ISO 750 (analytical methods referenced for maturity assessment)
- Annexes A–C in ISO 3631 give cultivar lists and common storage damage, aiding practical implementation.
Keywords: ISO 3631, citrus storage guidelines, refrigerated storage, pre-cooling, relative humidity, fungicidal treatment, wax coating, citrus cold chain.