I thought I would write a bit about the way meltwater of ice works to chill whole gutted fish when they are properly packed and iced, remembering that it is contact with meltwater of ice, not the ice itself that does the deep-chilling.
Before water changes from liquid to solid ice, an extra amount of heat first has to be removed from the water. This same amount of heat has to be added to the ice in order to change it back to water. The heat in the flesh of fish is thus removed by this “cold reserve” property of ice. But the magic thing about this is that both ice and its meltwater remain at the same temperature of 0 degrees Centigrade until ALL the ice has melted, having expended its “cold reserve”.
The fish packing method described here as shown in an attached photo is especially effective when dealing with medium to large size fish that will produce fillets that are an inch (2.5cm) or more thick along the backbone. This includes most of the snapper family (Lutjanidae), emperor family (Lethrinidae), rockcod, grouper and coral trout family (Serranidae) and many others.
Smaller fishes can simply be packed in alternate layers of ice and fish without the need for the fish to be placed in any particular position. Their smaller girth allows meltwater to chill them thoroughly.
Whether or not the fish have been prechilled in a slurry of ice and seawater (best practice) before being gutted, gilled and rinsed clean, take the time to remove as much of the kidney tissue that appears as a red streak along either side of the backbone. An old toothbrush helps with this chore. A final rinse and the fish are ready to pack in ice, but first a word about eskys or chilling boxes.
Although these are designed with a drain plug or tap to allow for draining meltwater, they usually lack a simple refinement in the form of a removable screen or perforated sheet of fibreglass that will prevent ice from mixing with meltwater and forming slush that impedes or stops the draining process. This is also a waste of ice because, as mentioned above, the temperature of any mixture of meltwater and ice will not rise above 0 degrees Centigrade until all the ice has first melted. The message here is: keep ice out of meltwater at the bottom of the chilling box by creating a shallow sump just above the drain level.
Whenever I buy an ice chest, I take it to a fibreglass wizard to have a tray made to fit over the lid of the chest in such a way that it can’t slide off in unkindly seas. The tray is made up with a hollow bottom and drain plug so that it may be filled with meltwater drained from the ice chest. One or two inches depth of meltwater should still leave the tray easy to shift to get into the ice chest. The tray’s drain/filler plug is made big enough for flushing the tray clean, as fishy meltwater is pretty awful when it warms up.
The message here is: make use of the 0 degree meltwater to help insulate a chilling box. Back to the method of packing whole gutted and gilled fish of medium to large size. Traditionally, such fish are packed upright, belly down in rows on a layer of ice, then topped with another layer of ice, etc., until the box is full. That’s the way I used until an elderly Japanese gentleman kindly provided me with a better method as shown in the attached photo.
His explanation turned out to be an embarrassingly simple lesson involving gravity and the flow of water. In the traditional packing method, even if ice is forced upward into the gut cavity of fish, all meltwater will flow downward away from the thick flesh adjacent to the backbone — just where it is most needed for chilling. Using the traditional packing method, thick flesh along a fishes back sheds meltwater originating from above because scales and slime offer little resistance to its downward flow. Chilling is less efficient.
By simply packing the fish belly-up and filled with ice, meltwater flows from top to bottom of the chilling box along more efficient pathways.
Now why didn’t I think of that?
Written by Don Tuma 2009