Fish is extremely sensitive to heat treatment; far more so than meat. But if you know what to look for, the fish will tell you exactly when it’s done, and it is very easy to get right. Easier than meat actually. Here’s how to cook fish like pro.
I fucking HATED boiled fish when I was a kid. Which was too fucking bad for little me, cause we had it at least two times a week. At least.
There was nothing wrong with the quality of the fish, cause my dad fished it himself, so it was always as fresh as a fish can be. And yet…
As an adult I have understood why I hated it so much, and I am convinced this is one of the main reasons why so many kids hate fish: Their parents simply does not know how to cook it properly, and end up with fish dry AF with a mouthfeel of sticky, grainy glue between your teeth. Which makes you eat it slow. Which makes it cold. Which makes it even worse. Especially when you must eat what’s on your plate.
I hope to remedy this with this tutorial, and help you churn out restaurant quality fish from your own galley or kitchen. Every. Single. Time.
TLDR; It’s all about hitting the right core temperature. The right core temperature depends on the type of fish. Below is a table with the correct core temperatures. Below that again you’ll learn exactly how to get there.
Core temperature table for fish:
|Species||Core temperature||Poaching & sous vide temperature|
|Cod||50-55C / 122-131F||60C / 140F|
|Mackerel||43C / 109F||43C / 109F|
|Skate||50C / 122F||55C / 131F|
|Angler||48C / 118F||60C / 140F|
|Halibut||55C / 131F||60C / 140F|
|Salmon||45-50C / 113-131F||55C / 131F|
Size doesn’t matter…
It’s how thick it is that matters; the thicker it is, the longer heat takes to penetrate. But whereas low heat will penetrate nice and slowly, high heat will penetrate more quickly.
To clarify: thermal physics dictates that a thick slab will need longer time to reach the same core temperature as a thinner piece – to reach thermal equilibrium with the poaching liquid for example.
“Boiling fish”: Poaching & sous vide
The key here is that you are not supposed to boil fish, but rather poach it. The traditional method is you bring a pot of salted water to a boil, then slip your fish into that water for 10-20 minutes or so, depending on the size of the fish.
And of course, this method will end up ruining an otherwise beautiful piece of fish.
Instead, bring a pot of well salted water, 25-30 grams sea salt per liter water, up to the temperature specified in the table above, then let it sit there for 10-15 minutes depending on the thickness of the fish. Once the fish starts to flake, that is the fish telling you “Hey man, I’m done!”
When using such low temperature, it is very hard to ruin the fish and a few minutes extra has relatively little impact on quality. But if you let it sit for too long, the protein will start denaturing, and become more and more “mushy” instead of nice and flaky.
Some will react to the incredible amount of salt in the water, but that is what you need to make the fish tasty. With such short contact time with the water, the fish will not at all taste salty, despite the water being near the salinity of sea water (world avg. 3.5%).
In fact you could use sea water for this if you pre boil it to kill off organisms, then cool it to 60C; all Norwegian shrimp is boiled in sea water, on the trawler, the minute the catch is hoisted onboard, and they taste amazing!
Pan-frying, searing & grilling
Never use a non-stick pan for frying anything, since high heat will destroy its non-stick layer; instead use a stainless steel or a cast iron pan for high heat searing. Instead, reserve your one non-stick pan for low temp egg dishes, like scrambled eggs, omelets etc . The pan will keep for a decade or more instead of just a few years before it’s worn out.
Note that a cast iron has better non-stick properties at lower heat than stainless steel. Some people love their carbon steel pans, and I’m sure they’re nice, but I promise you, they do not work on a boat, cause they rust the minute they’re unwrapped.
Step number one is to give the fish a sprinkle of fine sea salt at least 10 minutes ahead of searing. This will trigger a process called osmosis, and it will both firm up the fish, and make it supremely juicy, since it is able to retain much more of its juices.
So when your guests swoon and begs you to tell them your secret to fish…
When ready to grill or sear, wipe off moisture from the fish. This is a very important step, because if you don’t, you will waste a lot of thermal energy evaporating that moisture once it hits the heat, instead of browning the fish. And browning the fish is the whole point of searing and grilling.
In most cases, unless you have a very thick piece of fish, you cannot use high enough heat, so go as high as you possibly can. When your pan is smoking, add a moderate amount of neutral oil, then place the fish gently into the pan to prevent hot oil splashing all over the place. Do not use butter when frying fish, as it’ll only burn at this high heat.
If grilling, brush the fish with oil after wiping it dry, then place onto your hotter-than-hell grill grate. If the grill grate or pan is not hot enough, it will stick to the pan or grate.
As the heat starts to penetrate the fish meat, it’ll change colour; it’ll go from a translucent white (or pink if it’s salmon) to a opaque of the same colour, and you will clearly see this on the side of the fish fillet.
When the fish is opaque almost up to the center of the fish, it is time to gently flip it over. When the other side is opaque 2/3 towards the middle, turn off the heat. The residual heat in the pan will do the rest.
After just a few more minutes, it will have just become opaque all the way through, and that means it is perfect. If you let it sit a few more minutes, it’ll be overdone.
It is then better to take the fish off the pan and set aside to rest on a cutting board than let it sit longer in the pan if you’re not ready with the rest of your dish. The core temperature you’re after is 50-55C (122-131F) for cod.
With a very thick piece of fish, like in the recipe above, you need to use a lower temperature. In this recipe, I have also used the hazelnut crust, which works as a heat barrier, making it cook much slower on the crusted side, so that is why I use medium heat. With a thinner piece of fish, or without the crust, I would sear it off like a steak at medium-high to high depending on thickness.
With a very thin piece of fish, like mackerel fillet or a small flounder, like witch flounder, sear off only the skin side at very high heat, turn down the heat, add a knob of butter or additional oil, then spoon hot fat from the pan over the un-seared side. This will very gently warm the fish trough, and prevent it going dry on you. Serve immediately.
And that wraps up this tutorial! Check out our amazing fish recipes for something to practice on! If you have any questions, or tips of your own, please leave a comment below!