Cos Lettuce Post harvest: Why Structure Makes Moisture Control Even More Critical
Cos lettuce (romaine) carries the same core postharvest risk as iceberg — rapid moisture loss under cold storage — but its elongated, open head structure makes it even more exposed. More cut surface and leaf edge means faster water loss and quicker wilting, which is exactly what makes extended sea freight storage a challenge worth testing properly.
Moisture Loss and Leaf Quality: The Core Constraint
Because cos heads are looser and more open than iceberg, they lose moisture from a larger exposed leaf surface. Left unprotected in cold storage, this shows up as wilting, leaf yellowing, and rib discolouration well before the 5-week mark exporters need for sea freight. As with iceberg, the challenge is holding humidity high enough to prevent wilting without creating the condensation that drives rot.
What the Trial Showed
Biopac ran the same 5-week trial structure on cos lettuce alongside iceberg, packed 13 November 2020 in Brisbane and held at 2°C, comparing heads in Life Pack MAP bags (T2) against unbagged controls (T4). At the 3-week evaluation, the MAP-bagged cos heads were already holding a visible quality edge over the controls. By 4 weeks, the gap had grown — the control heads showed clear wilting and leaf collapse, while the bagged heads retained their structure.
At the final 5-week evaluation on 17 December, the control heads (T4) had reached unacceptable quality, with heavy wilting, moisture loss, and rib discolouration. The MAP-bagged heads (T2) remained in good, marketable condition, holding their leaf structure and colour where the controls had collapsed.
What This Means for Packaging
Cos lettuce’s more open structure makes it more sensitive to storage conditions than iceberg, which makes the Life Pack MAP bag’s humidity and condensation control even more valuable here. By keeping the head hydrated without pooling free moisture, the bag protects the exposed leaf surfaces that would otherwise wilt first — extending marketable quality through the full 5-week sea freight window.
The Practical Takeaway
Cos lettuce is a workable sea-freight crop when packed correctly, but the margin for error is tighter than iceberg given its structure. Life Pack MAP bags closed that margin in this trial: unprotected heads failed by week 5, while bagged heads did not — supporting cos as a viable export line for extended transit when packaging is part of the plan from day one.
Download the full iceberg and cos lettuce trial report (PDF)
Related: Cos Lettuce MAP Bag specifications
