Mistakes to avoid when defrosting fish

When defrosting fish, there are a series of very common errors that lead to waste, which mainly concern food safety and product quality.

Index of topics

Defrost at room temperature

One of the most common mistakes is placing fish directly from the freezer onto the countertop or sink: the surface of the fish can very quickly reach temperatures (between 5 and 60 degrees) that favor bacterial growth (the so-called "danger zone"), while the inside is still frozen and it will become very difficult to cook it properly and ensure good flavor and the right consistency of the dish you intend to prepare.

Use hot water

Hot water rapidly heats the surface of the fish, which can reach temperatures (about 5–60°C) favorable for bacterial growth, while the interior is still frozen. The longer the fish remains in this temperature range, the greater the microbiological risk. With hot water, thawing is uneven, and the heat can begin to partially "cook" the outer layers, degrading the fish's texture and flavor.

Pause and resume defrosting

Each freezing cycle Thawing promotes the formation of ice crystals that damage tissue cells. The result can be drier, softer fish that loses more juice during cooking. Furthermore, interrupting and restarting thawing can encourage both microbial growth and deterioration of the fish's quality. If the fish is left to thaw and then returned to the freezer, the outside may already have reached temperatures where the bacteria present can multiply.

Refreeze

If the fish has been completely thawed and kept out of the refrigerator, it should not be refrozen. The quality will deteriorate and hygiene risks may increase. However, if it has been properly thawed in the refrigerator and not cooked, it can sometimes be refrozen, but with a loss of quality.

Leaving it in the refrigerator too long after thawing

Once thawed, it's best to consume it within 24 hours (or according to the instructions on the package). Once thawed, microorganisms can start multiplying again, albeit slowly in the refrigerator. Also fish is a highly perishable food: Compared to many meats, it tends to spoil more quickly due to its composition and the enzymes naturally present in its tissues. Finally, its odor, flavor, and texture can deteriorate even if the fish is still safe to eat.

Do not collect thawing liquids

When fish thaws, it loses water and cell juices. These fluids may contain microorganisms naturally present on the fish or introduced during processing. If they drip into the refrigerator, they can contaminate other foods, especially those that will be eaten raw (salads, fruit, cheeses, etc.). It's best to place the fish in a container, bowl, or on a plate on the bottom shelf of the refrigerator.

Correct methods

These are the correct methods for defrosting fish.

In the fridgeThe safest method. Move the fish from the freezer to the refrigerator and let it thaw slowly for several hours or overnight. There's also a qualitative benefit: slow, controlled thawing in the refrigerator reduces liquid loss and helps maintain a better texture than thawing at room temperature.
In cold water: if you need it more quickly, leave the fish in a well-closed container immersed in cold water, changing the water every 30 minutes.
In the microwave: use the “defrost” function only if you intend to cook the fish immediately afterwards.

The only exception to these methods concerns some frozen fillets Thinner fish (e.g. cod, hake, or plaice) can be cooked directly from frozen following the manufacturer's instructions, without first defrosting.