Process — How frozen fish pies are produced

The diagram shows the thirteen steps involved in manufacturing frozen fish pies, using two parallel production lines.

Overall, the potatoes and the salmon are prepared separately and only come together at the assembly stage, after which the pies are frozen, packed and distributed. A further point of contrast is storage time: potatoes can wait for up to a month, whereas the fresh fish must be used within twelve hours of delivery.

On the potato line, the vegetables are delivered and stored, then washed and peeled. They are sliced by machine, boiled until soft, and finally mashed together with butter and milk. Meanwhile, on the fish line, fresh salmon arrives and is steamed whole for thirty minutes. The skin and bones are then removed by hand, and the flesh is combined with peas and white sauce.

At the assembly point, the fish mixture and the mashed potato are placed together in pie dishes. The assembled pies are frozen at minus thirty degrees Celsius, wrapped and boxed, and then transported in refrigerated lorries to cold stores, from where they are delivered to shops. From start to finish, the two ingredients follow entirely separate paths until the final quarter of the process.