By Harold McGee
Like finfish, squid and octopus maintain their osmotic balance largely with the tasteless TMAO rather than with free amino acids. Their flesh is therefore less sweet and savory than that of the other molluscs, and can turn fishy when bacteria convert TMAO to TMA.
Cephalopod ink is a bag of pigment that the animal can squirt into the water when endangered. It’s a heat-stable mix of phenolic compounds (animal cousins of the phenolic complexes that discolor cut fruits and vegetables), and cooks use it to color stews and pastas a dark brown.