A fused carton of individually quick frozen vegetables is the clearest single indicator that the cold chain moved, and it is a mechanical process rather than a mysterious one.
Each piece carries a thin surface layer of ice. When the temperature rises above the storage set point, some of that surface ice melts. When the temperature falls again, the liquid refreezes – but now it is in contact with the adjacent piece, and it freezes as a bridge. Repeat the cycle a few times and the recrystallisation process consolidates the whole carton.
Compression accelerates it. The bottom layer of a pallet carries the weight of everything above it, which is why fusion is almost always worst there and why a sample drawn from the top layer will pass while the consignment fails.
The practical consequences for a buyer:
- Free-flowing behaviour is the functional acceptance test, not appearance. A frozen carton always looks acceptable until someone tries to portion it.
- Sample from the bottom layer of the pallet, not the top.
- A fused lot cannot be restored. Breaking the block mechanically damages the pieces and produces fines.
- The evidence is in the temperature record. Specify continuous logging with the logger placed in the load rather than in the air return, and require the download as a condition of acceptance.
The contractual side matters as much as the technical one. Codex CXC 8-1976 is the handling reference and the ATP agreement covers the equipment class, but neither decides who pays. A contract that states a set point of minus eighteen degrees Celsius or colder, a defined tolerance for transient warming, and an explicit responsibility split for excursions is what turns a temperature record into a remedy.