Fooling Around on Friday
French Country Lamb Stew to the Rescue

The Science Behind Why It's Important to Undercook Fish

The other day, I was buying frozen salmon and I ran into my sister-in-law, who saw my purchase and asked me how I kept the fish from drying out when I cooked it. I didn’t have an answer, as I always undercook fish to keep it moist. I spent many years working in a retail fish market, and I learned that it’s best to turn off the heat when the fillet is still a little raw. Recently, I learned a bit more about why this is the case.

A colleague of mine who is about to give birth was recently cleaning out her desk, and she gave me an old copy of Cook’s Illustrated. I have mixed feelings about the magazine. I think it’s beautifully illustrated and written, but I sometimes stumble when I come face to face with their thoroughness. When they check something out, they go all out, testing things this way and that way and everyway in between. I’m more of a seat-of-the-pants guy, and I don’t necessarily need to know the best way to do something, just the way that works for me. And that is one of the things I love most about home cooking—do it your way, and enjoy it.

On the way home from work that evening, I read through my copy of the magazine. They spent about a thousand words on how to make the best salmon cakes, something I will never ever do, but a sidebar to that article intrigued me.  They examined why salmon sometimes tastes fishy, even when it’s fresh:

First it helps to know that there are two different kinds of ‘fishy’: one is a sign of spoilage; the other is an indication of the presence of healthy fats. The flesh of all fish contains an odorless, nonvolatile chemical called trimethylamine oxide (or TMAO). During storage, bacteria on the surface of the raw fish convert TMAO into a volatile compound called trimethylamine (TMA), which produces the unmistakable smell of rotten fish.

The fishy smell of cooked salmon (and other fatty fish such as mackerel and tuna) comes from a different source. Salmon fat is highly unsaturated, which makes it susceptible to oxidation when cooked. Oxidation causes the breakdown of the fatty acids into strong-smelling aldehydes, which are the source of salmon’s characteristic flavor.

Apparently, the more you cook the fish, the higher the level of aldehydes, and the stronger the odor. That night, I came into the house, and it was fragrant, well actually, pungent, with the smell of salmon. I had left some for the babysitter to cook for Nina and Pinta. I guess she doesn’t know to undercook the fillet. I’ll have to try and show her how to do so. If you want to try salmon cakes the Cook’s Illustrated way, here’s a link to their article and recipe.

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