Eli5: Why does seafood seem to spoil so quick?


Eli5: Why does seafood seem to spoil so quick?

In: 162

Most sea creatures contain a molecule called trimethylamine oxide (TMAO) in their flesh. The molecule helps balance their internal salt levels against the high concentration of salt in the water. It also helps with stabilizing proteins.

TMAO will break down (oxidize) when in contact with oxygen in the air. The oxidized chemicals produce the fishy smell for seafood that has been left out for too long and has spoiled.

Note that freshwater fish have much lower concentrations of TMAO so they don’t smell as strongly when left out.

Also sea creatures live at lower temps so they start to spoil at lower temperatures. That’s why fish are kept on ice in stores where red meat/poultry are kept in refrigerators.


In addition to the other reasons already posted, realize that most seafood is several days old by the time it gets to your supermarket. So, with its propensity for accelerated spoilage, it also has a head start on getting there in the first place before it’s even put up for sale.

Adding: a lot of the time, seafood have been killed by suffocating due to being out of water. Suffocating fish panic and flop around, which causes a buildup of stress chemicals that, combined with the blood not being drained, make the fish spoil faster.

The ike jime method of killing fish kills them instantly and drains their blood, meaning they dont flop around and cause the stress chemicals to build up, causing then to stay fresh far longer, and even allows for aging to build up a nice umami flavour. It’s not used often for fish caught en masse because it involves a lot of manual work, so ike jime slaughtered fish tends to be quite expensive.