Why Must You Always Freeze Fish If You Wanna Serve It Raw?

Raw fish is a culinary specialty that has attracted increasing interest over the years: the arrival of sushi and sashimi, in fact, has not only increased its consumption at restaurants, but also the curiosity to make carpaccio and crudités in general at home, moving from the more traditional plateaus, including crustaceans and molluscs, to recipes inspired by the Land of the Rising Sun. Hence, the need to be well informed on how to make raw seafood that is not only of excellent quality in terms of the final result of the recipe, but also not dangerous for health, thus avoiding potentially dangerous food poisoning such as that caused by anisakis, a parasite that is killed only by killing the fish. Let's see what it consists of, if it can be replicated home made and how to do it.

Why is Raw Fish Frozen?

The freezing of fresh fish is a practice required by American law to ensure the food safety of fish products to be eaten raw, in particular to eliminate anisakis, a parasite that can cause serious damage to human health: it is a very rapid cooling process that neutralizes the larvae. The indications are found in the FDA's Food Code which establish specific hygiene standards for foods of animal origin, including the obligation to freeze fish when served raw or semi-raw, even in marinated and smoked versions.

This means that the fish product is brought to a temperature of between -4°F (-20°C) and -31°F (-35°C) in a very short time: the operation can be carried out on board ships, preferably within 4 hours of fishing, in fishmongers, or inside restaurants, by transferring the fresh fish into the appropriate blast chiller. Catering businesses, therefore, must buy it already treated, or equip themselves with the appropriate tool, in order to offer raw fish.

What Happens if You Eat Unfrozen Fish?

Eating raw, unfrozen fish can lead to food poisoning with potentially very dangerous consequences. This procedure, in fact, is mainly applied to prevent the risk of anisakidosis, an infection caused by anisakis, a round, whitish worm (nematode) of the Anisakidae family that nests in the gastrointestinal tract of cetaceans and various fish species, from cod to salmon, with particular relevance in blue fish , including anchovies, sardines and mackerel, but also in cephalopods such as squid and calamari. We are talking about a small parasite, responsible for zoonoses, or diseases that are transmitted from animals to humans: how? Its larvae (measuring 15 to 30 mm) pass from the stomach into the fish meat, especially in the lower part and, once ingested, can affect the human intestine, causing disorders such as nausea, vomiting, diarrhea up to allergic reactions and perforation of the intestinal wall. Anisakis resists marinades and cold smoking, as well as refrigeration: it is destroyed by subjecting it to temperatures above 60 °C for 10 minutes or, indeed, by freezing.

How to Freeze Fish: The Grades and Procedure to Follow

In restaurants and fishmongers, chilling is performed with professional equipment called blast chillers: they are capable of reaching very low temperatures quickly, respecting the regulations that require bringing the fish product to -4°F/-20°C for at least 24 hours. For the preparation of raw fish at home, however, the term chilling is considered improper, as the freezer is not an appliance capable of chilling, but of freezing food: it may not reach such low temperatures and the cooling operation is slower. For this reason, the law adapts, and the Food Code in its guidelines recommends freezing fresh fish for at least 7 days at a temperature of -4°F/-18°C. However, care must be taken not to allow the product to undergo thermal variations, given that the freezer can often be opened and closed to use other foods stored inside. Below, here is the procedure to follow if you want to make home-made raw fish, recommending it to those who are already experienced in the kitchen and can count on a trusted retailer:

• Choose fresh, quality fish: these are the two fundamental characteristics for obtaining a good, guaranteed dish. In fact, freezing/chilling does not improve the product in terms of its organoleptic properties or sanitization: apart from anisakis, if other pathogens such as listeria, salmonella, escherichia coli or vibrio vulnificus are present, their proliferation is slowed down, but they remain (they are eliminated by pasteurization or sterilization, therefore only by cooking). Starting from excellent raw materials is a must. Make sure when purchasing that the fish has not been defrosted, because a food cannot be frozen/chilled twice.
• Thorough cleaning: the fish must first be gutted, so it must be free of entrails, blood residues, cut into slices or filleted. At this stage you can notice if there is the presence of anisakis larvae.
• Immediate freezing: transfer the fish to airtight containers or freezer bags to avoid contamination with other foods.
• Freezer storage: Set your freezer to the lowest temperature possible. It should be at least -4°F/-18°C and leave it for at least 7 days.
• Thawing: respect the cold chain, and transfer from the freezer to the refrigerator on the lower shelf, where temperatures do not exceed 5 °C. Consume within 24 hours.