Anisakis and freezing: a practical guide to eating fish safely

This parasite has changed the way we consume fish in recent decades, but that shouldn't be a reason to stop enjoying it. The solution is simple and effective: coldIn this guide we explain everything you need to know to eat fish with complete peace of mind, taking advantage of the safety of frozen products.

quick summary

To make it clear at a glance, these are the basic guidelines recommended by health authorities:

1. If eaten raw or semi-raw: Mandatory freezing (sushi, marinated anchovies, carpaccio).
2. If cooked properly (>60ºC): No need to freeze (fried, stewed, well-cooked oven).
3. Always maintain hygiene: Always defrost in the refrigerator to avoid bacteria, as the cold inactivates the parasite but does not sanitize the product.

What is anisakis and where is it found?

Anisakis is a parasite (a small white worm) that can be found in the digestive tract and muscles of many fish and cephalopods marine life. If we eat raw or undercooked fish containing live larvae, we can suffer an infection called anisakiasis or allergic reactions.

It is important to note that anisakis It is not a sign of spoiled fishIt is a naturally occurring organism in the marine ecosystem. It can appear both in the hake from the Cantabrian Sea, as with wild salmon. That's why prevention is key.

Freezing: The most effective method

The regulations are clear: cold inactivates the parasite. However, not all cold acts the same way or with the same speed. This is where we must differentiate between freezing at home and buying industrially frozen fish.

1. Industrial ultra-freezing (Very safe) The products deep-frozen and frozen Industrially, they undergo controlled technological processes that guarantee the effective inactivation of the larvae. Companies apply heat treatments equivalent to or exceeding the minimum requirements established by law to ensure the product is safe for consumption, even in raw preparations. Furthermore, because the process is so rapid, the texture and nutrients remain intact.
2. Home freezing (Requires time) If you buy fresh fish to freeze yourself, you'll need patience. Home freezers are less powerful than commercial ones, and it takes time for the cold to reach the center of the fish.

• The rule: According to AESAN, you must use a freezer of 3 stars () or more*. If your refrigerator doesn't have stars, it doesn't guarantee the necessary temperature.
• Time: To ensure safety, it is recommended to keep the product at a temperature of -20ºC or lower. For practical purposes, keep the fish frozen for at least 5 daysThis ensures that the interior has frozen properly and eliminates the risk.

When is freezing MANDATORY?

The risk of anisakis varies depending on the species and, above all, on however you're going to cook itYou must take extreme precautions and freeze beforehand if you are going to prepare:

• Raw fish: Sushi, sashimi, carpaccios or tartares.
• Marinated or vinegared fish: The classics anchovies in vinegar or the anchovy In salting. The acid and salt do not kill the parasite on their own; they require prior freezing.
• Undercooked preparations: Grilled fish that is undercooked or cold-smoked.
• Cephalopods: El octopus, the squid and sepia They can also be carriers and require the same precautions if not cooked thoroughly.

When is freezing NOT necessary?

Freezing isn't always necessary. If you buy fresh fish, the anisakis parasite will die from the heat. If you cook the fish in a traditional way, making sure that the center of the product reaches 60ºC for at least one minute, it is completely safe.

This applies to methods such as:

• Fry fish (Andalusian or Roman style).
• Stews and soups (where the broth boils).
• Baked fish cooked well (where the flesh separates easily from the bone).

Bivalves and aquaculture: What's happening with them?

There are exceptions where the risk is different:

• Bivalve mollusks: The oysters, clamsmussels or clams They do not suffer from anisakisBecause their filter-feeding system prevents the parasite from attaching to them, you can eat them raw or steamed without worrying about this parasite (although they should always be fresh and cleaned).
• Farmed fish: Fish raised in controlled environments and fed with parasite-free feed have a very low risk It is more likely to contain anisakis compared to wild fish. However, if it is going to be consumed completely raw, the general recommendation to freeze it remains a good preventative practice.

Step by step: From freezer to plate

Just as important as freezing is knowing How to properly defrost fish and seafood.

• Important Note: Freezing is very effective against anisakis, but It does not eliminate bacteriaIt only stops their growth. That's why, when thawed, they can reproduce again.
• How to do it: Always store it in the bottom part of the refrigerator (never at room temperature) and on a rack so the fish doesn't come into contact with the water it releases. This ensures complete safety: no parasites and no bacteria.

Frequently Asked Questions about Anisakis (FAQs)

Does vinegar or lemon kill anisakis? 

No. This is a dangerous myth. Neither the vinegar in anchovies nor the lemon in ceviche eliminates the larvae. Only freezing or heat (cooking above 60ºC) are effective.

If I'm allergic to anisakis, can I eat frozen fish? 

You must consult your doctor. Freezing kills the parasite and prevents gastric infection, but some highly sensitive individuals may react to the parasite's allergens even if it is dead.

Is anisakis visible to the naked eye? 

Sometimes, yes. They are small, thin, whitish worms, about 2 or 3 centimeters long. They are usually found in the viscera or coiled in the flesh near the abdomen. Cleaning the fish thoroughly (removing the guts) reduces the parasite load, but it doesn't guarantee complete safety if it isn't cooked or frozen.