Packing format
Pallet ventilation, and the warm core inside
Vent holes only work when they line up. Cross stacking holds a pallet together, but it turns every side vent into something that has to meet an end vent, so alignment becomes a design decision instead of an accident. Wrap the result in solid film and the channels lead nowhere, which is how a pallet that looks right arrives holding its heat.
The figures
| Vent area on the face meeting the airflow | As little as 5% of the carton face can be adequate, though 10% to 15% is more common |
|---|---|
| What has to line up on a cross stacked pallet | Side vents against end vents, so air passes through the cartons rather than around them |
| Ventilation rate cited for oranges in a transport space | 40 to 60 air changes per hour, with a continuous supply of fresh air |
| What a column stack gives | Continuous channels, and the least stable unit on the pallet |
| What restores stability to a column stack | Strapping, edge protectors, slip sheets and a top frame |
| What full stretch wrap does | Covers the vent rows it passes over |
| Where the honest temperature reading is | The core of the pallet, not the outer boxes |
| What we have confirmed about our own pallets | Nothing. Stacking pattern, film and vent design are all open |
What it changes on an order
You measure temperature at goods in
An outer box sits in moving air and reads what the trailer reads. Probe between the middle boxes of the middle layer, and where that is not practical, say in advance which reading the two sides will treat as binding.
You buy fruit that will be stored before it sells
Heat left in the core at loading is still there at delivery, and it comes out of shelf life at your end rather than the shipper's. That is a cost which never appears on an invoice.
You are looking at a supplier's photographs
Stacking pattern, strapping and the kind of wrap are all visible in a picture of a finished pallet. Ask for one before the first order and you will learn more than a specification sheet tells you.
What this note does not settle
- This explains why a pallet can cool unevenly. It does not tell you how a particular load behaved, which is a question for the temperature recorder that travelled with it.
- The vent area figures come from general produce cooling practice, not from a citrus standard. A carton designed for one commodity and one cooling method does not transfer to another without checking.
- Ventilation is one input among several. Fruit temperature at picking and the cooling step before loading decide more than the stack does, and they are covered separately.
Source: NC State Extension, Introduction to Postharvest Engineering for Fresh Fruits and Vegetables, produce cooling basics, Pathare and others, Design of Packaging Vents for Cooling Fresh Horticultural Produce, GDV Transport Information Service, oranges
Stability and airflow pull apart
The two things a packer wants from a stacking pattern work against each other. Boxes laid in the same orientation on every layer line their vent holes up into continuous channels, which is what cooling air needs, and produce a column that will happily fall over. Rotate the boxes layer by layer and the unit holds itself together, but the channels then survive only where the vents on the sides were cut to meet the vents on the ends.
A stacking pattern is a choice between two failures, and the usual resolution keeps the aligned pattern and adds the stability back with strapping, corner boards and a top frame. That spends money at the packhouse and saves it everywhere after. Which resolution a supplier has chosen is worth knowing, because the answer is visible in a photograph of the finished pallet.
The core is the reading that counts
Film finishes whatever the pattern started. A pallet wrapped solid from top to bottom is sealed, and the channels inside it now lead nowhere. Perforated film, banding at the corners alone, or a wrap that stops short of the vent rows all leave a load able to breathe, and all three look different from across a warehouse.
None of this shows in the fruit on the outside of the pallet. Outer boxes sit in moving air and read correctly on a probe, while the centre of the stack keeps the heat it left with. Where a pallet is going to disappoint, it disappoints from the middle outwards, and the middle is where the probe belongs.
Talk to the grower
Tell us the variety, the sizes and the delivery week you need. You get a delivered price and what we can commit to in writing, from the person who picks the fruit.
The grower handles enquiries. Response times are still to be confirmed.