What a modern reefer can and cannot do for your fruit

Your container held its setpoint for the whole voyage and the fruit still arrived soft. Or your exporter has quoted controlled atmosphere on a lane you have always run conventionally, and you cannot tell whether it is worth the money. Both are the same question underneath: what does the machine on the end of the box actually do, and what does it only appear to do?

A reefer removes heat. It does not add cold. #

A reefer is a refrigeration plant with a container bolted to it. The unit draws air out of the cargo space, passes it over an evaporator coil, and blows it back in colder. Cold is not something it adds — it is heat it takes away, at a fixed maximum rate.

Where that air goes matters more than most importers are told. Chilled air is delivered at the bottom of the container, through the ribbed T-shaped floor decking, and works its way up through the stow to a return grille at the top of the unit. The T-floor is the duct, not drainage. Block it — a pallet slid over the channels, a load stacked past the red line so air cannot get over the top — and the far end of the box starves while the unit reports that everything is fine.

That is also why the unit records two temperatures. Delivery air is what it is producing; return air is what came back after passing through the cargo. Chilled produce is controlled on delivery air, because that is the coldest air any of your fruit will touch. The gap between the two is the heat the load is giving off.

And because the plant is sized to hold a temperature rather than reach one, its capacity goes on two things: heat leaking through the walls, and heat the fruit is producing. Nothing is left over for pulling down a warm load. A reefer is not a pre-cooler and cannot be used as one.

The walls are the other half of the machine #

The container is a foam flask. Polyurethane is blown into the wall cavities, and the insulation is thick enough to cost you real space: a 40ft high-cube reefer offers roughly 67 m³ against roughly 76 m³ in the dry box of the same external size. That is about a pallet position you pay ocean freight on and cannot fill.

Foam ages. The gas trapped in its closed cells is slowly replaced by air over the life of the box, and the wall conducts a little more heat every year. Nothing announces this. An older container holds setpoint perfectly well in mild conditions and starts to struggle on a hot quay with a load that is respiring hard — which is the combination found on the lanes with the least room for error.

Insulation also buys the one genuinely forgiving property a reefer has. A pre-cooled, fully loaded box that loses power drifts slowly rather than warming immediately, because the fruit and the walls have thermal mass: hours, not minutes, and not days either. That is the difference between a terminal move with no plug, which is usually survivable, and a genset that quit on a long road leg, which is not.

Your setpoint is not your fruit’s temperature #

The unit conditions air. Pulp temperature — what the fruit is actually doing — follows slowly, from the outside of the pallet in, and only converges with the air if the cargo was properly pre-cooled before stuffing.

Fruit loaded warm sits above specification for days while the unit runs flat out and writes a flawless log. The paperwork shows a container behaving perfectly, because it was. The opposite error costs as much: dropping the setpoint “for safety” on a chilling-sensitive commodity causes internal browning, pitting or a failure to ripen at all — damage that develops well above freezing and stays invisible until the fruit is cut open. Treat the number as a specification, not a dial.

Controlled atmosphere, and what it is not #

Controlled atmosphere goes a step further than temperature. Fruit is alive and burning its own reserves; drop the oxygen in the container to a few per cent, raise the carbon dioxide, and that metabolism slows. Ripening slows with it, and on the right commodity CA buys real days.

Two things about it are worth being clear on. It is not the same as modified atmosphere, where a liner or a bag sets the mix once and then lets it drift — cheaper, genuinely useful, a different product. And the gas recipe is as commodity-specific as the setpoint: too little oxygen and the fruit ferments and tastes of it, too much carbon dioxide and you get CO₂ injury. Avocados, bananas and blueberries all ship under CA and none of them want the same atmosphere.

CA is specified, booked and paid for before the doors close. It is the tool for a lane at the edge of what the fruit will tolerate — which is why it has quietly become a lane-opening technology rather than an insurance policy. The six-week run from New Zealand to Rotterdam is the clearest case: nothing ships that far unless it stores, and what stores does so in CA.

The box now reports on itself #

New reefers ship with a modem, a GPS receiver and a controller that pushes readings off the box while it is on the water, and the major lines have wrapped that in a service — Maersk’s Captain Peter and Hapag-Lloyd LIVE among them.

What nobody tells you is how unevenly it lands. Coverage depends on the age of the box you were allocated, not on the carrier’s marketing. Sampling intervals differ, and an hourly reading and a six-hourly one are not the same evidence in a claim. Some lines push alerts; others expect you to log in and look. And if you booked through a forwarder rather than directly with the line, the data may not reach you at all, because the portal belongs to somebody else’s account.

So treat in-transit telemetry as a real improvement with an honest limit. It gives you the unit’s air temperatures, on the boxes that have it, at whatever granularity that line offers. It is not pulp temperature, and it does not replace pulling the full log on arrival.

What is changing under the lid #

Refrigerants. The refrigerant is the gas the unit pumps round to carry heat out of the box, and which gas that is has become a regulatory question rather than an engineering one. Most of the fleet still runs on R134a or R404A. Both are potent greenhouse gases, and Europe’s F-gas rules are squeezing them out on a published timetable, so new builds use blends with a fraction of the warming effect — R452A is the common one. The destination most of the industry expects is carbon dioxide itself: sold as R744, natural, and with nothing left to phase out afterwards. Carrier’s NaturaLINE showed it works at container scale. The catch is the step in between. Those synthetic blends break down in the atmosphere into TFA, a compound that does not degrade, and it has been pulled into Europe’s wider fight over PFAS — the “forever chemicals”. A replacement that has to be replaced again means the fleet turns over twice instead of once.

Energy. Reefers are the largest electrical load on a container ship, and every one is a cost the line carries for the whole voyage. Efficiency gains go straight to operating cost, which is why they get engineered hard and part of why reefer slots on a vessel are rationed the way they are. Both of these — the refrigerant and the energy — are also why a reefer’s carbon figure is not a dry container’s, which matters the moment a buyer asks for one: what actually drives your import carbon footprint covers what to add on top.

None of this is a purchasing decision for an importer. It matters because it sets the pace of fleet renewal, and fleet renewal is what decides whether the box you are allocated next season is well insulated with working telemetry, or fifteen years old with neither.

New technology opens new lanes, and new lanes have no slack #

The commercial consequence of all this is not “better boxes”. It is that cargo which used to fly now sails.

Chile moves a growing share of its cherries to mainland China by sea rather than by air. Peru ships blueberries into Rotterdam and on to the US on programmes that would not have held condition a decade ago. CA is what makes Peruvian avocados into Europe routine, and what puts genuinely long shots — Kenya into mainland China among them — on the table at all. Mangoes are the conversion most people are watching next. Which commodity crosses after that is a question with a framework behind it rather than a guess — the air-to-sea frontier is where we keep the map.

Here is the part that gets skipped. Each of those lanes works because the fruit now arrives with just enough life left, which is another way of saying the buffer has been spent buying the lane. A programme that used to absorb a five-day slip cannot absorb one when the transit already consumes most of what the fruit has. The same technology that made the lane possible removed the margin that made delays tolerable.

So as lanes stretch, finding out early stops being a nicety. A reefer that drifted in week two, a connection missed at a hub, a vessel that lost four days: annoyances on a mature short lane, the whole consignment on a marginal long one. You cannot stop any of them happening. What you can change is whether you hear about it while there is still a decision to make, and that is the job Trackberry does on the containers you already have on the water.

FAQ #

How do reefer containers work? #

A refrigeration unit draws air from the cargo space, cools it over an evaporator coil and delivers it back through the T-shaped floor decking so it rises through the stow. It removes heat rather than adding cold, and it is sized to hold a temperature rather than to bring a warm load down.

Why is a reefer’s internal volume smaller than a dry container? #

Because the walls are thick insulating foam and the refrigeration unit takes up one end. A 40ft high-cube reefer gives you roughly 67 m³ where the dry equivalent gives roughly 76 m³ — about a pallet position of space you pay freight on and cannot use.

Can a reefer cool down warm fruit? #

No. Its capacity is spent on heat leaking through the walls and heat the fruit is producing, so pulling down a warm load takes days it does not have. Field heat comes off at the packhouse; a container stuffed warm arrives with shelf life already gone and a temperature log that looks perfect.

How long does a reefer hold temperature without power? #

Hours rather than minutes if it was pre-cooled and fully loaded, because the fruit and the insulation have thermal mass — though it depends on ambient temperature and on what is in the box. A short unplugged terminal move is usually survivable; an unpowered road leg or an overnight wait for a plug is a real cold-chain risk.

Is controlled atmosphere worth paying for? #

On fast-respiring fruit over a long voyage, usually — several trades exist only because CA made the transit survivable. It has to be specified before loading, and the gas recipe is commodity-specific enough that getting it wrong damages fruit rather than merely wasting money.

Does smart reefer telemetry replace the temperature log? #

No. Telemetry gives you air temperatures during the voyage, on the boxes that carry it, at whatever interval the line samples, which is useful for catching a problem while you can still act. The full log downloaded on arrival is still the record that settles a quality claim.