Vol. VI · Proteins and Heat Plate 8 of 11fish, fish proteins, flaking, low temperature, overcooking, cod, salmonMH

Fish Proteins.

Fish lives in cold water, and its proteins are built for the cold. They give up at temperatures that would leave beef raw.

Fish muscle is made for life in cold water, buoyed up and needing no heavy frame. Its proteins unfold at lower temperatures than those of land animals — fish myosin in the forties — and its connective tissue is thin and dissolves easily, so cooked fish falls into flakes along its natural layers. A salmon fillet is translucent and buttery at 45 °C, opaque and moist at about 50–52 °C, and by 60 °C it is firm, flaky and beginning to dry; white fish such as cod is a few degrees higher.

The window between done and dry is therefore narrow and low, and fish overcooks in a minute where a steak takes five. The workshop poaches a fillet of fish and a slab of beef of the same thickness side by side.

Below: the centres of a 25 mm cod fillet and a 25 mm steak heated in water at the temperature you choose, with their usual targets marked.

What you will learn
Workshop
A 25 mm cod fillet and a 25 mm beef slab from 4 °C in water at the chosen temperature (thermal bench). Fish is usually served at 50–55 °C at the centre, beef medium-rare at 54–57 °C; the safety guidance for fish is 63 °C unless the fish is suitable for eating raw (XII.6, XIX.6).

A low, narrow window

In water at 70 °C the cod reaches 52 °C at its centre in 15 min and passes 60 °C only 5.4 minutes later; in a 90 °C poach the gap shrinks to 2.2 minutes. At 60 °C water it never goes past 60 — the gentlest way to cook fish is in liquid or a low oven only a little above the target, which leaves a margin of many minutes.

Two consequences follow. Fish wants gentle heat — poaching below a simmer, steaming over moderate heat, a low oven, or a very hot pan for a thin fillet's skin side only, then a moment on the flesh. And fish is judged by look and feel as well as temperature: the flesh turns opaque and separates into flakes under gentle pressure at the point of doneness. Safety guidance for fish is 63 °C, though fish handled and frozen for raw eating is served raw or barely cooked in many cuisines (XIX.6).

At the stove

Poach two pieces of the same fish, one in water at a bare shiver (about 70 °C) and one at a rolling boil, for the same five minutes. The boiled one will be firmer, drier and more broken up.

The muscle of cold-water fish contains antifreeze-like adaptations and enzymes that work at low temperatures, which is also why fish spoils faster than meat at refrigerator temperatures (XIX.2).

Terms

Flaking
Cooked fish separating along the thin sheets of connective tissue between its muscle layers.
Myotome
One of the blocks of muscle that make up a fish fillet.
Translucent
Raw fish's glassy look; it turns opaque as proteins set.
Carryover
Fish keeps cooking off the heat too; take it off a little early (II.8).
Fish proteins set in the forties and fifties; the window between done and dry is low and narrow. Use gentle heat.

Sources

  1. Differential scanning calorimetry of muscle: myosin denatures around 54–58 °C, collagen shrinks around 60–67 °C, actin around 70–80 °C (A. Wright, I. B. Leach and P. Wilding, "Differential scanning calorimetric studies of muscle and its constituent proteins", J. Sci. Food Agric. 28, 1977; H. McGee, On Food and Cooking, 2004). The course uses midpoints within these ranges.
  2. USDA Food Safety and Inspection Service, "Safe Minimum Internal Temperature Chart" (foodsafety.gov), 2024.
  3. H. McGee, On Food and Cooking: The Science and Lore of the Kitchen, 2nd ed., Scribner, 2004.