On Food and Cooking

the cold environment in which fish bodies
function (p. 189), their collagen differs from
mammal and bird collagens. Fish collagen is
less cross-linked, and so melts and dissolves
at much lower temperatures. The collagen and
gelatin of warm-water fish like tilapia melt at
around 77ºF/25ºC, that of cold-water cod
around 50ºF/10ºC. So we can extract fish
gelatin at cooking temperatures far below the
boil, and in relatively short times. The
collagen of squid and octopus is more cross-
linked than fish collagen, so these molluscs
require more prolonged heating at 180ºF/80ºC
to give up much of their gelatin. Most cooks
recommend cooking fish stocks for less than
an hour so as to avoid making the stock
cloudy and chalky with calcium salts from the
dis-integrating bones. Another reason for
short and gentle extractions is that fish
gelatins are relatively fragile and more readily
break down into small pieces when cooked.
And because they associate more loosely with