Freezing Fish for Parasite Control Before Raw Service

Freezing is the main control for parasites in fish served raw or lightly cured, such as sushi, sashimi and ceviche. Freezing to a low enough temperature for long enough kills parasites like Anisakis and fish tapeworm that would otherwise survive because the fish is never cooked. Commonly recognised parameters are minus 20C for seven days, or minus 35C for about 15 hours. Confirm the parameters that apply and keep records. Key takeaways: Cooking to 75C in the centre kills parasites, but raw and lightly cured fish is never cooked, so freezing is the control that does the same job.. Two widely recognised freezing parameters are minus 20C or colder for seven days, or minus 35C or colder for about 15 hours, measured at the coldest point of the fish.. Anisakis and fish tapeworm are the parasites of concern in many wild-caught species destined for raw service.. Domestic and display fridges and most home-style freezers cannot reliably reach or hold these temperatures, so the control usually needs commercial blast freezing or a validated supplier.. Freezing controls parasites only; it does not remove bacteria, viruses, histamine or allergens, and it must sit inside your wider food safety program with records to prove it happened.. Why freezing is the key control for raw fish Most parasite risk in fish is destroyed by thorough cooking. Heating fish so the centre reaches at least 75C kills parasites along with most bacteria and viruses. The problem with sushi, sashimi, ceviche, cold-smoked and lightly cured fish is that this step never happens, so the usual kill step is missing. Freezing to a sufficiently low temperature, held for long enough, is the recognised alternative. It physically destroys parasites in the flesh so the fish can be served raw. Curing in citrus, salt or acid, as in ceviche, changes the texture and flavour but does not reliably kill parasites, which is why freezing is still needed for those dishes. Because the fish is eaten uncooked, this is a genuine high-risk process. Freezing for parasite control should be treated as a critical step in your food safety program, planned deliberately rather than assumed to happen because product 'looks frozen'. Which parasites and which fish are the concern The parasites most often discussed for raw fish are roundworms such as Anisakis and, in some species and regions, fish tapeworm. They can be present in the flesh of a range of wild-caught marine and some freshwater fish. Eating them alive in undercooked or raw fish can cause illness, so removing them is the point of the freezing step. Risk varies by species, water of origin and how the fish was handled. Some wild-caught species carry a higher likelihood of parasites; certain farmed fish raised on managed feed in controlled conditions are generally considered lower risk, but this depends on the specific farming system and should be confirmed rather than assumed. The safest position for a food business is to treat any fish destined for raw or lightly cured service as needing parasite control unless you have clear, documented evidence that a recognised exemption applies to that species and product. Recognised freezing times and temperatures Two freezing parameters are widely cited internationally and in Australian guidance for destroying parasites in fish intended for raw consumption. The temperature must be reached at the coldest point of the fish, not just the freezer air, and held for the full time. Minus 20C or colder, held for at least seven days (a longer, gentler freeze suited to standard commercial freezers that can hold the temperature).. Minus 35C or colder, held for about 15 hours (a fast, deep freeze typically achieved with a blast freezer).. Some guidance also recognises freezing at minus 35C until solid, then storing at minus 20C or colder for a set further period.. Equipment: why a normal fridge-freezer is not enough The parameters above are demanding. A domestic or under-counter freezer often runs warmer than minus 20C, cycles through defrost, and is opened frequently, so it may never hold the coldest point of a thick fish fillet at the required temperature for the full period. Relying on it is a common and serious mistake. Meeting the control usually means one of two things: a commercial blast freezer that can drive the core temperature down quickly and be verified, or buying fish that a supplier has already frozen to a recognised parasite-control specification and can certify. If you rely on a supplier, get written confirmation of the freezing parameters used, keep it on file, and treat that documentation as part of your evidence. Storing already-treated fish is fine at normal frozen temperatures; the parasite-killing freeze is the step that must meet the specification. Records and evidence to keep Because raw fish is high risk and freezing is a critical control, you need to be able to show it was done correctly. Records turn a good intention into evidence an auditor or environmental health officer can verify, and they help you catch a freezer that is drifting warm before it becomes a problem. Where you do the freezing in-house, log the product, batch or delivery, the start and finish times, and the temperature achieved at the coldest point. Where a supplier does it, keep their specification or certificate for each batch. Link the record to the fish so you can trace which product was treated. Keep these records with your other food safety documentation, alongside receiving temperatures, cold-storage checks and cleaning logs, so the raw-fish process sits inside your overall system rather than off to one side. What freezing does not fix Freezing for parasite control is narrow: it destroys parasites, and that is all. It does not make unsafe fish safe in every other respect, so it must sit alongside your normal controls rather than replace them. Freezing does not reliably kill bacteria or viruses, and it does not reverse spoilage or reduce histamine (scombrotoxin) that can build up in fish such as tuna and mackerel if they are temperature-abused before freezing. Once thawed, treated fish is still a potentially hazardous, ready-to-eat food: keep it cold at or below 5C, handle it hygienically, prevent cross-contamination, and apply the 2-hour/4-hour rule to any time in the 5C to 60C danger zone. Allergen duties also continue. Fish and, separately, crustaceans and molluscs are declared allergens, so labelling and cross-contact controls under the allergen labelling rules apply regardless of freezing. Checklist: Every raw or lightly cured fish dish has been identified as needing parasite control unless a documented exemption applies.. Fish is frozen to a recognised parameter (for example minus 20C for seven days, or minus 35C for about 15 hours) at the coldest point.. The freezer used can actually reach and hold the required temperature (blast freezer or certified supplier, not a domestic unit).. Freezing records or supplier certificates are kept and linked to each batch.. Thawing is done under refrigeration at or below 5C.. Cross-contamination between raw fish and ready-to-eat food is controlled with dedicated equipment.. The 2-hour/4-hour rule is applied to any time the fish spends between 5C and 60C.. Fish, crustacean and mollusc allergens are labelled and communicated accurately.. Common mistakes: Assuming curing in citrus or salt (as in ceviche) kills parasites; it changes texture but does not reliably destroy them.. Relying on a domestic or display freezer that never reaches or holds the required core temperature for the full time.. Measuring only the freezer air temperature instead of the coldest point of the fish.. Keeping no freezing records or supplier certificates, so the control cannot be verified.. Treating freezing as a cure-all and neglecting bacteria, histamine, cold storage and cross-contamination after thawing.. Serving farmed fish raw as 'low risk' without documented evidence for that specific species and farming system..