Sous vide is a great technique for cooking, but the setup can get expensive for something you might use rarely. Fortunately, you can replicate an expensive sous vide setup with equipment you already have in your kitchen. This is not a very versatile setup, but it's GREAT for cooking fish or other things that cook fairly quickly.
Big pot with lid, freezer bag, thermometer (that's it!)
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Step 1: Preparation
Season your fillet with salt and any other seasonings you desire. Let it sit for at least 30 minutes and up to an hour. This lets the salt penetrate into the fish to season it throughout.
Step 2: Setup
Take your biggest pot. Fill it near the top with your hottest tap water. Ours comes out of the tap right at 130 degrees, which is perfect. If yours is a bit hotter, let it cool down for a few minutes or add a couple of ice cubes. If it's a little cold, just turn on the burner for 30 seconds and stir to warm it up and even out the heating.
Once it's at the right temperature, it should stay there for 10-20 minutes easily. Put the lid on top to retain the heat. This should be plenty of time to finish your fish. If you notice it is cooling down significantly, you can turn on the burner for 30-60 seconds to heat it back up. But don't be aggressive; as long as you're above your finish temperature you should be fine.
Step 3: Sealing the Fish
You are going to use the "water-displacement" technique. Put the fish in a freezer bag with at least an inch of space at the top. Take out most of the air and close the seal about 90% of the way. Then slowly lower into the pot. The water will force out all of the air. Then seal the top.
If your fish is fatty, you shouldn't need to add any fat (oil/butter) to the bag. But if it's a little lean (like halibut) you can add oil or butter to increase the richness as it cooks.
Step 4: Cooking
Now just let it sit in the water with the lid on for about 15 minutes. This is the only tricky part, because the amount of time it takes will depend on the thickness of the filet and the type of fish. Fortunately, it's only kind of tricky, because the beauty of sous vide is that it's difficult to overcook with it. 1) The water temp is close to the final temperature (for salmon somewhere around 120). 2) Everything is sealed together in the bag so it won't lose any moisture and dry out.
If you have a fairly large pot, and you keep the lid on, you won't lose much heat. As you can see in the picture, ours went down 4 degrees in 10 minutes which still leaves it at a good temp if you needed to cook for a bit longer.
Step 5: Enjoy!
You'll know when it's done when the proteins just start to render out. You'll see it as a little white material along the surface of the fish. You can also check the internal temperature. As you can see in the header photo, ours was 119 degrees after ten minutes. For my taste, this is perfect. The other photo shows that the fish is just barely done through. Just on the edge of translucent.
Take it out of the bag and put it on a plate. You can add a little lemon or whatever, but if you've used good fish, it won't need anything special. Once you've had fish this way, you may not want it any other.
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