Fish to eat raw should always freeze. This is because fish contain parasites and the only way to kill them is to freeze the fish.
A small side jump. You should also fresh beef to tartar cows get parasites in the body like fish. Unfortunately, I do not know if beef to tartar is frozen. But I do not think so.
Now back to the fish. It is not the same type of parasite found in e.g. in tuna as in the salmon. This is because there are 2 very different fish species that primarily eat very differently.
In addition, the fish structure of the salmon and the tuna is very different and also affects the parasites found in the two different fish.
How long the fish should freeze is not the same and it depend again whether there is a whitefish, salmon or tuna.
At Sushi course for beginners I will talk more about the Japanese rules for freezing fish. The Japanese rules are more strict then the Danish rules. I choose to follow the Japanese rules as they know more about fish for sushi. In addition, I would also like to be on the safe side.
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Zoë has held sushi courses and cooking classes for A. P. Moller – Maersk, Hugo Boss Nordic, Novo Nordisk, Novartis, Velux, Gorrissen Federspiel, Beierholm revision, Elbek & Vejrup and many more.