How to Defrost Fish Quickly and Safely

We love having frozen fish on hand for quick, delicious fish dinners any night of the week. Seriously, frozen fish is one of the great innovations of the culinary world. In the old days, you could never know for sure if the fish you were buying was truly fresh. Today, most fish and seafood is flash frozen right on the boat within minutes after it's caught, preserving its peak freshness and ensuring that it stays fresh all the way to your kitchen. 

It's even packaged in vacuum sealed portions, for extra convenience—you can cook up enough fish for one person or a feed a whole family. All you need to do is defrost the fish and cook it. There are two preferred methods for thawing frozen fish, and which one you'll use mainly depends on how much time you have. 

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If You Have Time, Defrost Fish in the Refrigerator Overnight

One of the safest and best ways to defrost fish is in the refrigerator overnight. All you have to do is remember to move it from the freezer to the fridge before you go to bed and it'll be thawed and ready to cook the next day. If the fish is thin enough, you might be able to get away with putting it in the fridge in the morning if you're planning to cook it that night for dinner. Here's how to do it.

• If your fish is vacuum sealed, before placing it in the fridge, cut at least a small hole in the packaging or remove the packaging altogether—it's important to introduce oxygen to the fish to prevent the possible growth of anaerobic toxins.
• Place the fish on a plate or tray or put it in a sealable bag and then on a plate or tray and put it in the coldest part of your fridge (typically a shelf near the back).
• When you are ready to cook, dry the fish with paper towels, and you're all set to prepare it as you normally would!

If You're Short on Time, Defrost Fish in Cold Water

The next best way, and it's quite a bit quicker, is to defrost your fish in cold running water. This technique should take no more than 30 minutes, and can take even less time for thinner fillets.

Because it completely envelops the fish, cold water will thaw it faster than the cold air of the fridge. And even a tiny stream of water will produce a slight convection effect, which will speed the process significantly. Here's how to fast-track your fish dinner by thawing the fillets in water.

• If the fish is not already sealed in moisture-proof packaging, transfer it to a plastic freezer bag, squeeze out as much air as possible, and close it tightly. Whatever you do, don't submerge fish in water if it isn't sealed in plastic. This will cause it to become waterlogged. (Note that for this shorter method there is not a safety concern about leaving the fish in vacuum-sealed packaging, but the fish should be removed from the vacuum packaging as soon as it's thawed.)
• Place the fish in its packaging in a shallow dish in the sink, fill it with cold water, and leave the faucet running a tiny bit so that a narrow stream of water runs into the dish. Make sure the water is cold, not warm, and definitely not hot.
• Begin checking the package after 10 minutes to see if the fish is thawed—you should be able to tell just by feeling it and seeing if it has some give.
• Once the fish is thawed, remove it from the water and its packaging and dry it with paper towels.
• Cook as you usually would.

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How NOT to Defrost Fish

With these two easy, safe methods available, there's really no reason to try anything else. But in case you're tempted, here are some ways not to defrost fish:

• In warm water: This might seem faster than cool water, but it's a food safety hazard. If that's not reason enough, it can also give the fish a mushy, unpleasant texture.
• At room temperature: Thawing any perishable food, including fish, on the counter at room temperature is a big food safety no-no.
• In the microwave: Although the FDA says you can defrost fish in the microwave as long as you plan to cook it immediately, we don't recommend this method. The microwave heats unevenly, and might end up cooking parts of the fish while leaving the rest raw or frozen. This not only harms the texture of the fish, but if you don't cook it immediately, it can be dangerous from a food-safety standpoint too.

Why It's So Important to Thaw Fish Properly

The main concern when defrosting frozen fish is food safety. By that we mean minimizing the growth of bacteria that can cause food poisoning. And it turns out that the most efficient ways to defrost fish also happen to be the safest.

Both the refrigerator method and the cold water method outlined above are designed to keep fish out of the food safety danger zone of 40 F to 140 F—it's at these temperatures that bacteria grows the fastest. As with all perishable foods, never leave raw or cooked fish at room temperature for more than 2 hours, or more than 1 hour if the temperature is above 90 F.

Also be sure to wash your hands before and after handling the fish, to thoroughly clean any tools or surfaces that touched the fish, and to discard the packaging the fish came in or that you transferred it to.

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Why Does Frozen Fish Sometimes Turn Mushy?

Once thawed, fish can sometimes have a mushy texture. This can happen if you submerge the fish directly in water without tightly sealing it in plastic, so avoid doing this.

But there's another factor that can cause this, though it's pretty rare. Fish, like all living things, is made up of millions of cells, and these cells contain liquid. When fish is frozen, that liquid also freezes. If the freezing process happens too slowly—i.e. if the fish wasn't flash-frozen properly—that liquid can form ice crystals that will rupture the cells of the fish. When that fish is later thawed and cooked, this liquid will leak out, producing a mushy texture. 

Thicker steaks and fillets, because they take marginally longer to freeze, are more likely to have this issue, although if it's been frozen properly, it shouldn't be a problem. But assuming you defrosted it properly, if this does happen, it was most likely caused by something that occurred before you bought the fish, not by the way you thawed it—in other words, it's not your fault!