This diagram shows that there are a number of processes involved in the commercial production of frozen fish pies.
The main ingredients consist of fresh salmon, peas and sauce, with sliced potatoes, and they are prepared separately. The potatoes, which may have been delivered up to a month in advance, are cleaned, peeled and cut into slices. The slices are boiled and then chilled before being stored until needed. The preparation of the fish is more labor intensive than the preparation of the potatoes. Within twelve hours of being delivered to the factory, the fresh fish is cooked by being steamed with lemon juice and salt. Then the skin and bones are removed by hand and disposed of, before a visual inspection takes place.
After this, the pies are assembled in microwaveable containers. Peas and sauce, which have also been prepared, are added to the fish and then the pie is covered with a layer of cooked potato slices. The pies are then wrapped and frozen. At this point, they are ready for dispatch, or they may be stored at the factory before being dispatched.