Raw fish and parasites

What it is

Freezing at a specified temperature for a specified time kills parasites; most published guidance gives −20 °C for seven days, or −35 °C for about fifteen hours, measured throughout the fish. A domestic freezer often cannot reach or hold those temperatures.

Why it works

Freezing addresses parasites, not bacteria. Bacterial safety in raw fish comes from how it was caught, chilled and handled, which is why freshness, cold chain and a supplier you trust matter as much as the freezing step.

When to use it

Sushi, sashimi, ceviche, crudo, gravlax, tartare, kinilaw, poke.

What goes wrong

Assuming "sushi grade" is a regulated term, which in many places it is not; freezing in a domestic freezer and treating that as equivalent; assuming acid in a ceviche cooks the fish — it firms the protein and does not make it safe.

More on this shelf

Cassava and cyanogenic glycosides Why cassava must be processed before it is eaten, and why traditional methods are the safety step.
Cooked rice and Bacillus cereus Why leftover rice needs handling more carefully than most cooked food.
Cooling cooked food safely Getting hot food out of the danger zone quickly, which is harder than getting it in.
Cross-contamination How raw food makes cooked food unsafe, and the small habits that prevent it.
Home canning and botulism Why low-acid food in sealed jars needs a tested process, not a household one.
Reheating leftovers How hot, how often, and what will not be fixed by reheating.
Safe internal temperatures The internal temperatures published guidance gives for cooked food, and how to measure them.
Thawing safely The three safe ways to thaw frozen food, and the one everybody uses that is not.
The temperature danger zone The temperature range in which bacteria multiply fastest, and how long food may spend there.

Raw fish and parasites

What it is

Why it works

When to use it

What goes wrong

More on this shelf

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