United States
Hong KongFreezing fish for parasite destruction: the two options
Fish served raw or undercooked must be frozen at -20°C (-4°F) or below for 168 hours, or at -35°C (-31°F) until solid and then held at -35°C (-31°F) for 15 hours. Records of the treatment must be retained.
Two numbers, and both are unusual enough that they are worth learning as a pair rather than trying to reason from anything.
| Method | Temperature | Time |
|---|---|---|
| Conventional freezing | -20°C (-4°F) or below | 168 hours, which is 7 days |
| Blast freezing | -35°C (-31°F) until solid | Then held at -35°C (-31°F) for 15 hours |
| Blast freeze then conventional storage | -35°C (-31°F) until solid | Then held at -20°C (-4°F) for 24 hours |
Most domestic and many commercial freezers do not reach -4°F reliably, which is the practical reason this treatment is usually done by the supplier rather than in the restaurant. Check the spec.
What it is for
Parasites. Anisakis and related nematodes in marine fish, and tapeworms in some species.
Cooking to 145°F destroys them. Where the fish will not be cooked - sushi, sashimi, ceviche, cold-smoked, marinated but not cooked - freezing is the substitute kill step.
It is a marketing term with no regulatory definition. The Food Code asks about parasite destruction treatment and the records proving it, not about a label on a box.
Which fish are exempt
- Molluscan shellfish
- Certain aquacultured fish raised in open water on a formulated feed free of live parasites, most commonly farmed salmon
- Certain species of tuna, listed by the Code
- Eggs of fish that have been removed from the skein and rinsed
Tuna is the one worth remembering, because it explains why a sushi restaurant can serve some fish untreated and not others. It is a listed exemption.
Records
Where the establishment freezes the fish itself, records of the treatment are retained for 90 days beyond the sale or service of the fish. Where a supplier does it, written agreement or documentation from the supplier is retained instead.
A restaurant serving raw fish with no documentation of parasite destruction has a finding, however good its supplier is.
What freezing does not do
It does not destroy bacteria, and it does not destroy toxins.
Scombrotoxin in tuna and mahi-mahi forms when the fish is not kept cold enough after catch, and freezing later does nothing about it. Which is why receiving temperature still matters for fish that will be frozen anyway.
Common questions
How long must fish be frozen for parasite destruction?
168 hours - seven days - at -20°C (-4°F) or below. Blast freezing at -35°C (-31°F) until solid, then held at that temperature for 15 hours, is the faster alternative.
Does "sushi grade" mean anything?
No. It is a marketing term with no regulatory definition. The Code asks about documented parasite destruction treatment, not about a label.
Which fish are exempt from freezing?
Molluscan shellfish, certain aquacultured fish raised on formulated feed free of live parasites such as farmed salmon, certain listed tuna species, and rinsed fish eggs removed from the skein.
What records are required?
Where the establishment freezes the fish, records of the treatment kept 90 days beyond sale or service. Where a supplier does it, written documentation from the supplier.
Does freezing kill bacteria?
No. Freezing addresses parasites only. Bacteria survive and resume growing on thawing, and toxins such as scombrotoxin are unaffected entirely.