How do you keep fruit and vegetables fresh longer on a ship?

Why does produce spoil so fast in a ship's provision room?

Fruit and vegetables are still alive after harvest. They keep respiring, and many release ethylene, a plant hormone that speeds up ripening in everything around them. In a closed cold room, that ethylene accumulates. One box of over-ripe apples can shorten the life of the lettuce on the next shelf.

Three things work against a ship's store in particular. First, there is usually one vegetable room, set at a single temperature, holding produce that would ideally be stored at very different ones. Second, the room is sealed for weeks, so ethylene and mould spores build up rather than dispersing. Third, it is cold and humid, which suits mould on produce, packaging and the evaporator coils.

Most ship provision plants follow the same pattern. Meat and fish rooms run at about −18 to −20 °C. Vegetable and dairy rooms run at about +3 to +6 °C, with some plants holding them nearer 0 to +4 °C. Dry stores sit at ambient temperature.

What are the options for keeping provisions fresh at sea?

There are seven practical approaches. They are not alternatives so much as layers, and the cheap ones come first.

Temperature and humidity discipline. Cold slows respiration and ethylene production, but different produce wants different temperatures. Apples, pears and berries keep best at about +2 to +5 °C, potatoes and onions at +6 to +10 °C, and bananas at +13 to +18 °C. Bananas stored in a +4 °C vegetable room suffer chilling injury. Where a ship has a lobby or handling room at a warmer set point, use it for the produce that dislikes the cold.

Segregation. Apples, pears, ripe bananas, tomatoes and stone fruit are strong ethylene producers. Leafy greens, broccoli, cucumbers and carrots are sensitive to it. Keeping the two groups apart, even at opposite ends of the same room with the evaporator fan between them, costs only discipline.

Fresh-air ventilation. Opening the room to outside air dilutes ethylene, but it also disturbs the temperature and humidity the refrigeration plant is trying to hold, and it costs energy to pull the new air back down to temperature. On a ship in the tropics it is rarely practical.

Potassium permanganate filters or sachets. Permanganate oxidises ethylene chemically and is the most common ethylene absorber in the food trade. It works, but it is a consumable that must be renewed as it is used up, it takes up space, and it is toxic, so it must not touch the produce. It does nothing for mould spores or bacteria in the air.

Photocatalytic units (UV plus titanium dioxide). A UV lamp activates a catalyst surface that oxidises ethylene. Research interest is high, and published trials often combine photocatalysis with permanganate filters and forced airflow rather than using it alone.

Contained UV-C with low-level ozone. Units such as the JIMCO MAC500 pull the room's air past a UV-C lamp. One wavelength breaks down microbes and organic molecules passing through; a second turns a small amount of oxygen into ozone, which continues oxidising ethylene and odour in the room. They run continuously with people present and have no filters.

Ozone flooding. A generator fills an empty, closed space with ozone for a deep clean of the air and every surface. It is effective against mould and odour, but nobody can be in the space during treatment, and the room must be ventilated before re-entry. It suits an emptied store between voyages, not a working vegetable room.

How do the options compare?

What does the ethylene figure actually mean?

For a contained UV-C unit, the useful number is the ethylene removal rate, and it is worth reading carefully. The Danish Technological Institute tested the JIMCO MAC500s in a 20 m³ room and measured ethylene breaking down at up to 1.6 mL per hour, at concentrations falling from 6 ppm to 3 ppm. That is 1.5 to 2 % of the room's ethylene removed each hour. With the unit switched off, the natural decay rate was about a fifth of that.

DTI added two pieces of context. Real fruit and vegetable stores normally sit below 1 ppm, not at 3 to 6 ppm. And a tonne of apples gives off about 10 mL of ethylene per hour.

Put those together and the picture is clear. Because the unit removes a percentage of whatever ethylene is present, it removes less in absolute terms as the concentration falls. In our own arithmetic, at 1 ppm a 20 m³ room holds about 20 mL of ethylene, so a 2 % hourly rate takes out about 0.4 mL an hour. In a larger room, the same unit treats a smaller share of the air each hour. That is a real reduction, but it is nowhere near a tonne of apples' output.

The honest caveat: an air purifier is not an ethylene scrubber

A contained UV-C unit slows ethylene build-up. It does not hold ethylene near zero against a large load of high-emitting fruit. If the vegetable room is packed with apples and bananas next to lettuce, segregation will do more for the lettuce than any unit on the bulkhead.

So where does the week come from? Crews on Arnold Mærsk and Mette Mærsk reported about seven extra days after fitting a unit in each refrigerated room, according to JIMCO. The likely answer is that ethylene is only part of it. The same unit is cutting airborne mould spores and bacteria, which is what actually rots produce once ripening has started. In a laboratory test in Singapore, airborne bacteria fell by about 74 % and fungi by about 82 % within 45 minutes. That effect, alongside slower ethylene build-up and good storage practice, is a more believable explanation than ethylene removal alone.

There is a second limit, and it is a hard one. JIMCO rates the MAC500 for 4 to 45 °C. That covers most vegetable, dairy and lobby rooms, but not a room held at +2 °C, and certainly not a freezer. Check the set point before specifying one.

Is ozone safe in a provision room with the crew working in it?

At low concentrations, yes, and the type of device matters more than the gas. Contained UV-C units like the MAC500 make ozone deliberately but in small amounts; the UL-certified MAC500s is certified under California's 0.050 ppm ozone-emission limit for indoor air cleaners. That is what allows it to run around the clock in an occupied store, cabin or mess. Ozone flooding units are a different category. They raise the concentration high enough to sanitise every surface, so treat any use of them as an enclosed-space operation: nobody in the space, and ventilate before re-entry. Ozone is heavier than air and collects in low spaces.

In short

• Do the free things first: hold the vegetable room at the right temperature, put cold-sensitive produce somewhere warmer, and keep ethylene producers away from leafy greens.
• Then treat the air: a contained UV-C unit per 60 m³ is the only option on this list that works on ethylene, mould spores and odour at once while the room is in daily use, for 25 W and one lamp a year.
• Keep ozone flooding for empty spaces, and do not put any MAC500-type unit in a freezer room.

Frequently asked questions

Talk to us about your provision rooms

SepcoTech supplies JIMCO's MAC500 and OZ series to ships from Roskilde, Denmark. Send us your room volumes, set temperatures and the supply on board, and we will tell you how many units you need, which build suits each space, and where a unit is the wrong answer. The hardware, warranty and test documentation are JIMCO's; the stock, the EUR quote with no hidden import costs and support in your time zone are ours.

tech@sepcotech.com · ShipServ TN 317548