Iceberg Lettuce Fails at 5 Weeks Without MAP — Here’s the Trial Data
Iceberg lettuce is a demanding candidate for long-distance sea freight. It’s over 95% water, has a high respiration rate for a leafy crop, and is prone to pink rib — a discolouration of the mid-rib that develops under stress and moisture loss during storage. For exporters looking to move iceberg by sea rather than air, the postharvest window has to stretch to 5 weeks or more, well beyond what open storage can reliably deliver.
Moisture Loss and Pink Rib: The Core Constraint
Iceberg’s biggest enemy in extended cold storage isn’t ethylene sensitivity — it’s water loss. As the head loses moisture, outer leaves wilt and the rib tissue develops the reddish-brown discolouration known as pink rib, a quality defect that makes a head unsaleable well before it actually spoils. Controlling humidity around the head, without allowing condensation to pool and encourage rot, is the balance that determines whether a 5-week sea freight target is achievable.
What the Trial Showed
Biopac ran a 5-week storage trial on iceberg lettuce packed 13 November 2020 in Brisbane, comparing heads sealed in Life Pack MAP bags (T1) against unbagged control heads (T3), all held at 2°C. At the 3-week mark, the MAP-bagged heads were already showing a clear quality advantage over the controls. By 4 weeks, the difference had widened further.
By the 5-week evaluation on 17 December, the result was decisive: the control heads (T3) had reached unacceptable quality, with high levels of pink rib and significant moisture loss. The MAP-bagged heads (T1), by contrast, were still in good, marketable condition — firm, hydrated, and free of the discolouration affecting the controls.
What This Means for Packaging
The result comes down to the Life Pack MAP bag’s ability to control humidity and condensation together, rather than trading one off against the other. Sealed storage keeps moisture around the head high enough to prevent wilting and pink rib, while still allowing normal cooling airflow inside the bag — avoiding the free water buildup that would otherwise accelerate rot. That combination is what let the bagged heads hold marketable quality a full two weeks longer than the unprotected controls.
The Practical Takeaway
For exporters targeting sea freight over air, this trial supports iceberg lettuce as a viable candidate for extended transit — provided it’s packed in a MAP bag from the start. Unprotected heads reliably fail by week 5; bagged heads reliably don’t. That’s the difference between a shipment that arrives sellable and one that doesn’t.
Download the full iceberg and cos lettuce trial report (PDF)
Related: Lettuce MAP Bag specifications
