A berry export lane: pads, packs and a ten-day shelf

The first pallet of the season leaves the packhouse at 04:20 with fruit at 1.8 °C and arrives at the importer on day nine reading 4.6 °C, with condensation on the inside of the lid and a grey mould starting on the top layer of two punnets. The grower’s first reaction is that the gel packs were too small. The importer’s first reaction is that they were too cold. Both are wrong, and the answer is in the gap between the fruit and the pad.

Berries are the least forgiving payload in a chilled lane. They generate heat after picking, they lose water faster than almost any other crop, and they bruise at the slightest pressure. A lane that holds 2 °C beautifully can still deliver mouldy fruit, because temperature is only one of three variables you are managing.

Heat of respiration is a moving target

Picked strawberries at 20 °C can produce heat at a rate that will warm a full pallet by several degrees over a day if the air is not moving. Cool them to 2 °C and respiration drops by roughly a factor of five, which is why pre-cooling matters more than pack weight on this lane. Gel packs cannot outrun respiration in a warm pallet; they can only hold a pallet that has already been cooled.

This is the first place growers lose the ten days. Fruit goes into the box at 8 °C because the pre-cooler was full, the packs fight a losing battle for the first twelve hours, and the whole curve shifts up by three degrees for the rest of the journey. Fix the pre-cooling and half the pack weight problems disappear.

Where the pad and the pack divide the work

The absorbent pad under the fruit has one job: take up the juice and the wash water that comes off the berries so it does not sit in the base of the punnet. The gel pack has a different job: hold the air temperature in the box. Confusing the two is common, and it produces punnets with three pads and no packs, or packs sitting directly on the fruit.

Place packs against the inner wall of the master carton, separated from the punnets by a corrugated divider at least 3 mm thick. Contact between a pack at minus 18 and a berry at 2 °C produces a local freeze within minutes, and a frozen berry collapses on thaw and leaks. That leak then soaks the pad, softens the punnet and gives Botrytis a wet surface to start on.

The humidity trap in a sealed carton

A sealed master carton with cold packs and respiring fruit becomes a small humid chamber. Water condenses on the underside of the lid, drips back onto the top layer, and by day six you have a wet patch on four punnets and a customer claim. Perforated liners and a small vent pattern reduce this, but the real fix is to keep the temperature stable: condensation happens when surfaces cycle above and below the dew point, and a box held at a steady 1 °C condenses far less than one swinging between 0 and 5.

This is where gel packs earn their place on a berry lane. Not as a cooling device, but as a damper. A pack with a phase change near 0 °C absorbs the small heat spikes from a dock or a door opening, and it is those spikes, not the average temperature, that put water on the lid.

What to measure across ten days

Three loggers per pallet: one at the top layer, one in the middle, one at the base, all under the lid rather than in the air. Plus a simple weight check on one punnet per layer at dispatch and arrival, because a 1.5% loss is normal and a 4% loss means the fruit is dehydrating and the pad is not doing its job.

Then open one carton at arrival and photograph the lid before you touch anything. The pattern of condensation tells you more about the lane than the temperature graph does: water on the lid means the box cycled, water in the base means the fruit was warm when it was packed.

If you are specifying packs for a soft-fruit lane this season, the phase-change options in our SAP powder range include grades tuned to sit near 0 °C rather than the usual minus 18, which is what a berry box actually needs.

Run one pallet with lid-level loggers and one punnet weigh-in per layer before the season starts. Ten days of data will tell you whether your problem is pre-cooling, pack placement or the carton itself, and only one of those costs money to fix.