A practical, calculator-style playbook for stopping container rain in green coffee shipments. Includes exact desiccant sizing for 20ft and 40HC containers, placement maps, rainy-season adjustments, and answers to the questions shippers actually ask.
If you’ve ever opened a container in Europe or the U.S. after a tropical loading in Indonesia and found wet corrugations and stained jute sacks, you know “container rain” is real. In our experience, most coffee damage happens not because teams don’t care, but because desiccant planning is either under-sized or badly placed. Here’s the simple, 2025-ready system we use to size and position desiccants for Indonesian coffee exports.
Why container rain happens on coffee
Green coffee is hygroscopic. Jute and wood pallets breathe. A hot, humid stuffing day in Belawan or Surabaya meets a cool ocean night. Moist air condenses on cold steel, then drips onto sacks. Ventilation helps, but it can also bring in humid air at port. So we control what we can: moisture in the coffee, desiccant capacity, spacing to metal walls, and placement that intercepts drips before they hit the bags.
The 2025 coffee container desiccant calculator
We keep this practical and conservative. It’s tuned for Indonesian green coffee in jute or PP-lined bags, ocean transit 20–45 days.
Rule of thumb: use high-capacity calcium chloride desiccant. Assume 1 kg of desiccant safely absorbs about 2.5 kg of water over the voyage.
Start with a base load, then adjust for transit, season, moisture, packaging, and container type.
Required desiccant (kg) = Base + Transit + Season + Coffee MC + Packaging + Container
- Base: 20ft = 8 kg. 40HC = 16 kg.
- Transit: +0.5 kg per week beyond 3 weeks (20ft). +1 kg per week beyond 3 weeks (40HC).
- Season (Indonesia rainy months, typically Oct–Apr in Java/Sumatra): +25–40% of subtotal depending on local humidity at stuffing and port dwell.
- Coffee moisture content (MC): Ship at 10.5–11.5% MC. If 12.0–12.5%, add +10–15%. Above 12.5% MC, we don’t ship without corrective drying.
- Packaging: Jute = baseline. PP-lined bags can reduce vapor exchange. You may reduce desiccant 10–15%, but don’t go lower if you expect temperature swings. Poly overwrap on pallets often traps moisture. Avoid it.
- Container type: Ventilated container reduces peak condensation but not vapor ingress. Reduce desiccant by 10–20% only if stuffing and dwell are dry. Full container liners reduce dripping but not humidity. Keep 20–40% of the normal desiccant as a buffer inside the liner.
Quick example A (20ft, 18–19 tons, Surabaya to EU, 32 days, rainy season, jute):
- Base 8 kg + Transit 1 kg (two extra weeks × 0.5) = 9 kg.
- Season +30% = 11.7 kg.
- Coffee MC 11.5% = +0 kg.
- Packaging jute = +0 kg.
- Container GP = +0 kg.
- Round up safety. Use 16 kg total (eight 2 kg poles). In our shipments we often go 18–20 kg during peak rains if port dwell is long.
Quick example B (40HC, 26–28 tons, Belawan to U.S. West Coast, 28 days, dry season, PP-lined bags, ventilated):
- Base 16 kg + Transit 0 kg.
- Season +0%.
- MC 11.0% = +0 kg.
- Packaging PP-lined = −15% → 13.6 kg.
- Ventilated = −10% → 12.2 kg.
- Round up to 14–16 kg (seven to eight 2 kg poles). We rarely go below 16 kg if the route crosses large temperature gradients.
What’s interesting is that under-sizing by “just a few kg” can be the difference between dry corrugations and visible drips. We’d rather oversize by one or two poles than explain stains to a buyer.
Placement that actually stops drips (desiccant placement map)
Sizing is half the job. Placement is what prevents droplets from ever touching a bag.
- Sidewalls, high and even. Place poles along both side top rails, 20–30 cm below the roof, spaced 80–100 cm apart. They should be free-hanging, not buried behind sacks.
- Door header and corners. Add short bags/poles near the door header and rear corners. Doors are common drip zones after night cooling.
- Keep air gaps. Leave 8–10 cm between cargo and sidewalls. Don’t “press” sacks into corrugations. Use dunnage and corner boards to hold gaps.
- Top protection. If you top-cap pallets, use breathable kraft or felt pads, not plastic that traps moisture.
Quick placement pattern
- 20ft: 6–10 poles total. Typical map = 3–4 per side + 2 near doors. In heavy-rain shipments we add two across the front bulkhead.
- 40HC: 12–18 poles total. Typical map = 5–7 per side + 2–4 near doors/front bulkhead. Use additional short bags mid-roof if you see past drip marks.
We’ve found that evenly distributing capacity along the top side rails, not clustering at the doors, is the single best fix for drip lines across the middle row of sacks.
Seasonal and route adjustments for Indonesia
BMKG and international outlooks are signaling wetter-than-normal conditions for parts of Indonesia into early 2025. That means higher humidity at stuffing and longer port dwell in rain. Practical tweaks we use:
- Add 2–4 kg during Oct–Apr if your stuffing yard is outdoors or semi-open.
- If your route includes equatorial crossings and cool arrivals (e.g., Rotterdam, Hamburg, Busan in winter), keep the higher rainy-season factor even if stuffing day is “sunny.”
- Surabaya/Belawan to EU is commonly 28–35 days. To U.S. West Coast 25–30 days, East Coast 40–45 days. Those extra two weeks to the East Coast usually justify 4–6 kg more in a 40HC.
Need help right-sizing for your exact lane and dwell time? Send your route, transit days, bag type, and stuffing conditions and we’ll run the numbers with you. You can reach out via WhatsApp.
Answers to the questions we get most
How many desiccant bags are needed for 18–19 tons of green coffee in a 20ft container?
For 25–35 days at sea: 16–20 kg total in rainy season, 12–16 kg in dry season. That’s typically 8–10 poles of 2 kg each. We round up if port dwell is wet.
Where should I place poles and bags so drips don’t hit the coffee?
High along both side top rails, evenly spaced, then reinforce doors and front bulkhead. Keep 8–10 cm wall clearance. Don’t bury poles behind sacks. Imagine a “halo” around the cargo at roof level catching vapor before it condenses.
Do I still need desiccant if I use a full container liner?
Yes. Liners reduce dripping and shield from wall sweat, but humidity inside the liner still rises. Keep 20–40% of normal desiccant capacity inside the liner. We also add two short bags at the liner door area.
What moisture content should green coffee be to minimize condensation?
Target 10.5–11.5% MC. Indonesian exports usually specify max 12–12.5% by SNI/common buyer specs. Above 12.5% dramatically increases mold risk and desiccant can’t fix that. We always verify MC on the stuffing day.
Does a ventilated container reduce the need for desiccant with coffee?
It helps flatten temperature swings and can lower peak RH, but it still exchanges moist air. We reduce by 10–20% only when stuffing and dwell are dry. If it’s rainy, we don’t reduce at all.
How does Indonesia’s rainy season change desiccant requirements and placement?
We add 25–40% capacity and we focus extra poles at the door header and roof midline, where we’ve seen drips form after monsoon-night cooling. If your yard is wet and pallets might wick moisture, add more than the minimum.
What size desiccant works best with jute vs polypropylene bags?
Jute breathes. Use higher-capacity calcium chloride poles (1.5–2.0 kg each) and avoid small clay sachets as your main line of defense. With PP-lined bags you can trim capacity slightly, but keep at least 80–90% of the jute plan on long, cool-arrival routes.
Quick packing checklist we use in our own exports
- Coffee MC: 10.5–11.5%. Confirm on stuffing day. If a lot is borderline, we hold or recondition. For example, we ship Sumatra Mandheling Green Coffee Beans only after MC passes our pre-load check.
- Pallet moisture: kiln-dried or confirmed <18% MC. Wet pallets have ruined more containers than most people realize.
- Gaps: 8–10 cm from sidewalls. Don’t over-pack to the corrugation.
- Top cover: breathable kraft, not plastic. Plastic traps moisture.
- Desiccant: size with the calculator above. Use leak-proof CaCl2 poles. Place high on both sides plus door/bulkhead reinforcement.
- Final look: close at dusk if possible to avoid bringing in hot daytime air, or ventilate briefly before final seal if the stuffing bay was very hot and humid.
If you’re building seasonal blends, it’s also worth noting that some coffees travel more forgivingly. For instance, our washed lots like Arabica Bali Kintamani Grade 1 Green Coffee Beans and structured Sumatran profiles like Blue Batak Green Coffee Beans hold up very well when packed at 11–11.5% MC with a proper desiccant map.
Final takeaways
- Use calcium chloride desiccants and size them with a simple, conservative calculator. Err on the side of more, not less.
- Placement matters as much as kilograms. Build a “halo” along the top side rails and reinforce doors and bulkhead.
- Adjust for rainy season and route temperature drops. Indonesia to cool-climate arrivals needs extra capacity.
If you want a container-specific layout for your next shipment, send us your lane, transit time, and bag type. We’re happy to share a desiccant placement sketch we’ve used for EU and U.S. lanes. You can also browse the coffees we export and plan ahead for your 2025 bookings here: View our products.