Iranco Magazine Team
Engineering, thermodynamics, international standards and economics for food export logistics
Export Guide · Logistics · Cold Chain
Food Export Container Shipping: Dry vs Reefer
Engineering, thermodynamics, international standards and commercial trade-offs for Iran’s food export logistics.
Sustainable food exports depend on disciplined logistics. Iran ships fresh produce, nuts, frozen seafood, dates and canned goods to Russia, EAEU, the Gulf, India and Europe — routes that expose cargo to extreme heat and humidity swings.
Choosing a standard dry steel box versus an insulated reefer with active cooling is not only about ocean freight: it reflects respiration rate, dew point, voyage length, quarantine rules and contract margin. The wrong box invites claims, demurrage and brand damage.
Dry vs reefer technical comparison
| Index | Dry 40' | Reefer 40' | Food export relevance |
|---|---|---|---|
| Shell | Single Corten steel | Alu/PU sandwich | Block solar gain |
| Floor | 28 mm wood | Aluminium T-bar | Even cold airflow |
| K-value | Very high | <0.4 W/m²K | Limit heat ingress |
| Set range | Ambient follow | −30 to +30°C | Chilled/frozen band |
| Humidity | None | 55–95% RH | Mould/wilt control |
| Ventilation | Passive vents | 0–280 m³/h | Ethylene/CO₂ purge |
| Power | None | 380–460 V | Port/vessel/road |
Product-based container matrix
| Food group | Box | °C | RH | Vent m³/h | Wrong-box risk |
|---|---|---|---|---|---|
| Apple, kiwi, grape | Reefer | −0.5 to 1 | 90–95% | 15–25 | Ripening, mould |
| Leafy veg | Reefer | 8–12 | 90–95% | 20–30 | Wilting/freeze |
| Frozen fish/meat | Reefer | −18 to −22 | — | 0 closed | Ice recrystallisation |
| Mazafati dates | Reefer | −4 to 0 | 60–65% | 0 | Souring |
| Luxury pistachio | Mixed | 10–15* | <60%* | 0 | Aflatoxin |
| Aseptic paste | Mixed | 15–18* | Neutral | 0 | Colour browning |
| Chocolate | Reefer | 16–18 | <50% | 0 | Fat bloom |
* when reefer used or hot lane
1. Structural and thermodynamic comparison
Dry boxes are single-skin Corten steel without insulation; solar gain can push headspace above 65°C and drive moisture from wooden pallets and cartons. Reefers are insulated sandwich panels (K < 0.4 W/m²K) with microprocessor-controlled cooling. Bottom air delivery via T-bar floor channels forces cold air up through pallets; dry boxes rely on tiny passive vents. Reefers pass pre-trip inspection (PTI); dry units get visual checks only.
2. Iranian export food matrix
Respiring fruit (e.g. kiwi 0–0.5°C, 90–95% RH) needs reefers. Frozen seafood/meat stays at −18°C with vents closed. Mazafati dates need 0 to −4°C; semi-dry Piarom/Zahedi may move dry in cool seasons. Summer pistachios need 10–15°C and RH <60%. Aseptic paste and chocolate need reefers on hot lanes (15–18°C).
3. Container rain and dew point
Day-night cycles in dry boxes saturate headspace then condense on the steel ceiling — wet cartons, mould on nuts, can corrosion. Mitigate with calcium chloride desiccants (up to 300% uptake, irreversible gel) versus silica gel (~30%, reversible in heat), plus wall strips, ceiling blankets and thermal liners where appropriate.
4. Advanced reefer atmospheres
0–280 m³/h fresh air removes ethylene/CO₂ from fruit; controlled atmosphere (2–4% O₂) extends apple/kiwi voyages; active dehumidification 55–95% RH for onions and kernels; frozen loads keep vents fully closed to protect coils.
5. ATP and regulations
ATP class FNA (K≤0.7) for 0 to +12°C chilled produce; FRC (K<0.4) holds −20°C at +30°C ambient — mandatory for frozen shrimp/meat to EU/Russia. ATP plates renew every three years. EC 853/2004, US FSMA and GCC GSO require continuous temperature records.
6. Thermal liners in dry boxes
Reflective multi-layer liners blunt diurnal swings for stable goods (paste, pasta, dry dates) on short lanes; they are passive and equilibrate after 2–3 weeks — never for live respiring fruit.
7. Stowage and airflow
Respect the red load line to keep return air to the evaporator. Pre-cool cargo 24–48 h; do not pre-start reefers before loading unless from a cold tunnel. Align carton vents with pallet slots; block floor gaps; avoid non-breathable stretch wrap.
8. Economics
Reefer base ocean freight ~1.8–3× dry; plug power USD 50–120/day; genset USD 80–150/day; reefer demurrage USD 100–250/day; insurance +25–50%. On a USD 300k pistachio FCL, USD 4k tropical reefer premium is often <1.5% of cargo value.
9. Iran transit corridors
Gulf: greenhouse veg needs 2–6°C reefers despite short feeders. North: −20°C winters need heating mode for kiwi. India/China: CA for apples; FRC −22°C for shrimp. Iraq: confectionery/dairy reefers; canned dry.
10. Importer checklist
Contract container type; PTI certificate; set-point tolerance; vent rate or “vents closed”; pre-cooling protocol; ≥2 data loggers; ATP plate; carton/pallet alignment; road genset; negotiate free time.
11. Rate enquiry data
HS code, box type, temperature, dehumidification, fresh-air rate, weight/pallets, packaging, ports, Incoterms, genset/liner.
12. Supply via Iranco
Iranco matches international buyers to Iranian producers, cold stores and exporters against technical specs — from samples to delivery.
Logistics cost balance
| Cost item | Dry | Reefer | Basis |
|---|---|---|---|
| Base ocean | Index low | 1.8–3× | Reefer capex |
| Port power | — | USD 50–120/day | 3-phase plug |
| Road genset | — | USD 80–150/day | Transit energy |
| Deposit | Low | Up to 5× | Mechanical risk |
| Free time | 10–14 d | 3–7 d | Asset turn |
| Demurrage | USD 20–50 | USD 100–250 | Clearance delay |
| Insurance | Standard | +25–50% | Cold-chain clauses |
Conclusion
Container choice balances product biology, heat engineering, law and landed cost. Dry boxes work for shelf-stable cargo only when thermal liners and calcium-chloride desiccants control container rain; live fruit, frozen protein, dairy and premium nuts need reefers, pre-cooling, stow discipline and independent data loggers.
FAQ
Can turning down the reefer replace pre-cooling?
No — the unit only offsets wall heat gain. Warm loading freezes coils and ruins cargo.
How does container rain form?
Daytime heating loads vapor; at night the steel ceiling drops below dew point and drips.
Why calcium chloride over silica gel?
Up to 300% irreversible uptake; silica releases moisture again in heat.
What is the red load line?
Return-air plenum to the evaporator; over-stacking blocks airflow to the rear third.
Sourcing Iran with cold chain?
Submit specs on Iranco for vetted farm and cold-store options.
ATP FRC class?
Heavy insulation K<0.4 holding −20°C at +30°C ambient for frozen protein.
Summer pistachios in a dry box?
No — interior can exceed 50°C, accelerating rancidity and aflatoxin risk.
Freight quote inputs?
HS code, set-point, humidity, vent rate, weight, pallets, ports, Incoterms.
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