Fresh produce is the only cargo that is still alive when the doors close. It respires, consuming oxygen and giving off carbon dioxide, water, heat and ethylene. Everything about shipping it is an attempt to slow that process down without stopping it.
Cold is a rate control, not a pause
Lowering temperature slows respiration, which is why almost all produce ships chilled. But colder is not always better, and this is where inexperienced shippers do real damage.
Tropical and subtropical fruits suffer chilling injury below a threshold that is well above freezing. The symptoms appear after arrival, when the fruit is warmed for sale, so the damage is discovered by the customer rather than in the terminal:
- Bananas: below roughly 13C, the skin blackens and the fruit will not ripen properly
- Mangoes: below roughly 10 to 13C, pitting and uneven ripening
- Avocados: below roughly 4 to 7C depending on variety and maturity, grey flesh discolouration
- Pineapples: below roughly 7 to 10C, internal browning
Meanwhile apples and pears ship happily at 0C to 1C, and citrus typically at 4C to 8C. There is no single produce temperature, and a setpoint copied from the last shipment is a genuine risk. See reefer setpoints, ventilation and humidity.
Ethylene: the ripening hormone
Ethylene is a gas produced naturally by ripening fruit, and it accelerates ripening in anything sensitive to it. So one commodity can ruin another simply by being in the same container.
- High producers: apples, bananas, avocados, tomatoes, melons, pears, peaches, apricots, plums
- Highly sensitive: lettuce and leafy greens, broccoli, carrots, cucumbers, kiwifruit, asparagus, cut flowers
Do not mix a high producer with a sensitive commodity, even for a short leg. Kiwifruit stored near apples softens to unsaleable in days. Where mixing is unavoidable, ethylene absorbers based on potassium permanganate can help, but the reliable answer is separation and adequate fresh air exchange to flush the gas out.
Controlled atmosphere
A controlled atmosphere container actively manages the gas mix, typically pulling oxygen down to around 2 to 5 percent from the 21 percent in air, and holding carbon dioxide at a commodity specific level. Less oxygen means slower respiration, which means a longer shelf life.
What it buys is reach. CA is what makes it commercially possible to send avocados from Peru to Europe, or apples from New Zealand to the northern hemisphere, by sea rather than air. Extensions of several weeks are routine on the right commodity.
Three things to know:
- It is separate, scarcer equipment and must be booked as such well in advance. It cannot be switched on at the terminal.
- The gas recipe is commodity specific. The wrong mix causes fermentation and off-flavours rather than preservation.
- It is not a rescue. CA slows the decline of good fruit. It does nothing for fruit loaded too ripe or too warm.
Modified atmosphere, by contrast, is passive: the packaging and the produce's own respiration establish the gas mix, with no active control. Cheaper, less precise, common at retail pack level.
Cold treatment is a different thing entirely
Several importing countries require a quarantine cold treatment against fruit fly: the cargo must be held at a specified low temperature, often between 1C and 3C, for a specified number of consecutive days in transit, with calibrated probes inserted into the fruit pulp and a certified record.
This is a phytosanitary requirement of the destination, not a carriage decision, and it fails if the temperature rises above the threshold for even a short period. A failed cold treatment means the consignment is refused entry or must be re-treated, and it is one of the few situations where the carrier's data trace is the legal document.
Practical checklist
- Get the carriage temperature from the exporter's own protocol, per commodity and variety.
- Pre-cool the fruit before loading. A reefer will not do it. See what to specify.
- Set the fresh air vent to the commodity rate, not to habit.
- Never mix ethylene producers with sensitive cargo.
- Book CA early if the transit time demands it.
- Confirm cold treatment requirements with the destination plant health authority before the vessel sails.
General guidance. Carriage temperatures, gas mixes and cold treatment protocols are commodity and country specific, and come from your exporter protocol and the importing country plant health authority.
