Scope. This page provides a controlled reader-run protocol and does not claim site-run measurements. For cooking, cooling, storage and reheating, follow the current official guidance linked on the page.
Read this first: a cure is not a cook
The single sentence that matters on this page is that curing fish in salt and sugar does not cook it. It is not a mild cook, not a partial cook, not a chemical equivalent of cooking. The fish comes out of the cure raw.
This is worth stating flatly because the misconception is the mechanism by which people get hurt. Gravlax looks different from raw fish. It is firmer, darker at the edges, opaque rather than translucent, and it slices like something that has been through a process. All of that is protein denatured by salt and by the removal of water, and none of it is heat. The visual cues a cook uses to judge doneness in the doneness windows by species do not carry across. A cured fillet that looks cooked has told you about its salt content and nothing else.
Two consequences follow, and both are structural rather than fussy.
The safety of a cold cure is decided before the cure, not during it. Whatever risk the fish carries when it goes into the salt is broadly the risk it carries when it comes out. The controls that matter are the sourcing and the freezing treatment, and those happen upstream. No amount of extra salt, extra time or extra care in the curing stage substitutes for them.
Sensory checks are not a safety test here. A cured fillet that smells clean and tastes good may still be something you should not eat. Where spoilage or hazard is not detectable by smell, taste or appearance, and in this category it frequently is not, your senses are giving you a comfortable answer to a question they cannot address.
There is no room-temperature stage anywhere in this method. Not for curing, not for equalising, not for bringing it to serving temperature. If a recipe you are reading has one, that is where to stop reading it.
Sourcing and freezing: what the named authorities require
This section is the entire safety case for the dish, and it is the section this site will not write in its own words.
The relevant issue is that some fish carry parasites, and that eating fish raw or cold-cured means the treatment that addresses them has to have happened before it reaches you. Several national food-safety authorities publish specific requirements: a freezing temperature, a duration at that temperature, and a set of conditions and exemptions around species and farming method. Those requirements are precise, they differ between jurisdictions, and they are exactly the kind of figure a drafting process is tempted to round.
The governing source is linked rather than condensed into a household shortcut:
- FDA's commercial/retail parasite-destruction time-and-temperature options: Food Code §3-402.11, checked 21 August 2026.
- Species, aquaculture and processing exceptions: read the same section; do not assume every fish is covered identically.
- Domestic freezer capability: not established by that rule. A thermostat setting does not prove the product met the schedule throughout.
- Other jurisdictions: consult the current rule for the place where the food will be served; this page does not merge different legal regimes.
That last point deserves emphasis. Do not reconcile different jurisdictions into a single schedule or pick the easiest option: use the rule that applies where the food will be served.
What we can say without a citation, because it is a purchasing practice rather than a threshold:
Ask the seller a specific question, not a general one. "Is this sushi grade" is not a specific question; the phrase has no consistent regulatory meaning in most markets and a seller can answer it honestly while telling you nothing. The specific question is whether this fish has been through a parasite-destruction freezing treatment, at what temperature, and for how long. A good fishmonger can answer that or find out. If the answer is vague, treat it as a no.
Buy from somewhere that can trace what it sells. The relevant information travels with the fish through the supply chain or it does not exist. A counter that knows its supplier can retrieve it.
Do not assume that a fillet you froze at home satisfies the requirement. Whether a domestic freezer reaches and holds the necessary temperature is a matter for the cited guidance and for a thermometer, not an assumption. Many do not.
Do not treat any fish as safe to cure without meeting the cited sourcing conditions. Not because it came from a good shop, not because it is farmed, not because it looks perfect, and not because a recipe you like does not mention the issue. Most gravlax recipes in circulation say nothing about any of this, which is the reason this post exists.
The cure: ratio, weight, time, temperature
The mechanics. Where a number matters, it comes from the validated recipe you follow or from a named authority; this page supplies none of its own.
The ratio is by weight. Salt to sugar, and both against the weight of the fish, on a scale, in grams. Volume measures are unusable for salt because crystal shape varies enormously between types, so a spoonful of one salt and a spoonful of another differ in mass by a wide margin. A recipe that says "half a cup of salt" is not specifying a cure, it is describing one loosely, and the difference shows up in the finished fish as much as anywhere.
This page gives no ratio. Take it from the validated gravlax recipe you follow, weigh it rather than measuring by volume, and record the ratio, the fish weight and its thickness every time, as brines and cures describes for seasoning brines.
The temperature is refrigerated throughout. The cure runs in a refrigerator at 40°F (4°C) or below, consistent with FDA consumer seafood-storage guidance. There is no counter, garage or “cold kitchen” version on this site.
Cure duration is a recipe variable, not a parasite control. A thick centre-cut piece and a thin tail piece will season differently in the same time. This page supplies no universal cure duration, and curing does not replace the separate parasite control or safe storage.
The mechanical parts, which carry no safety figure and can be described plainly: the fish sits skin-side down in a non-reactive dish, covered in the cure mixture and any aromatics, wrapped, and weighted. Liquid draws out and pools, and most methods drain it or turn the fillet so that both faces spend comparable time in contact with the liquid. The flesh firms progressively and the colour deepens from the outside in. Rinsing at the end removes surface cure; drying before slicing makes slicing considerably easier.
Slicing. Thin, on a shallow angle, with the sharpest long knife you own, away from the skin. This is the one part of the process where practice visibly beats equipment.
What is actually happening to the fish
Salt does three things at once, and separating them explains most of what people find confusing about cures.
It draws water out of the flesh by osmosis, which concentrates flavour and firms the texture. It penetrates the flesh, and salt inside muscle tissue changes how the proteins interact, which is the same mechanism that makes a brined piece of meat behave differently under heat. And it changes the environment inside the fillet in ways that matter for what can grow there, which is the part that connects to the safety section rather than the flavour section.
Sugar and the traditional dill, pepper, juniper, spirits or citrus are treated here only as flavouring. This page assigns none of them a pathogen or parasite control function.
The visible result is a fillet that has lost mass, gained firmness, and turned opaque. It is worth repeating that this appearance is produced by salt and dehydration. The fish is raw. That is the whole reason the sourcing section sits above this one.
Cold-smoked fish, which pairs a cure with smoke below the temperature at which fish cooks, carries its own additional considerations and is not covered here.
Storage and serving
Storage figures are cited or absent:
- Refrigerated storage: 40°F (4°C) or below, from FDA consumer seafood guidance.
- Gravlax-specific storage duration: no FDA consumer figure located in the reviewed guidance, so this page gives none and does not borrow the raw-fish purchase window as a cured-product claim.
- Freezing after curing: not presented here as a way to restart or extend a storage clock.
- Once opened and sliced: keep refrigerated and minimise handling; no product-specific duration is invented.
Handling points that carry no figure:
Keep it wrapped and cold, and take out only what you are about to slice. A fillet that spends twenty minutes on a board each time somebody wants two slices has had a different history from one that does not.
Label it with the date it went into the cure and the date it came out. The discard decision depends on the timeline, and a timeline reconstructed from memory is how people end up relying on a smell check.
Use a clean board and a clean knife, and do not use the board that raw fish sat on for anything else without washing it. Cross-contamination is a bigger contributor to domestic illness than most of the exotic hazards people worry about, and it is the easiest thing on this page to control.
Serve it cold. There is no reheating step and nothing about serving it warm improves it.
Who is commonly advised to avoid this, per cited guidance
Several national authorities publish advice on raw and cold-cured fish for specific groups, typically including people who are pregnant, young children, older adults, and people who are immunocompromised or have certain medical conditions.
FDA identifies pregnant people, children, older adults and people with weakened immune systems as higher-risk groups and advises them to avoid raw or undercooked fish and shellfish. Read the current wording on the FDA consumer seafood-safety page; this article does not soften or reinterpret it.
If you are in any of those groups, or cooking for someone who is, the correct source is the authority in your jurisdiction, not a food publication and not a recipe.
A lower-risk alternative. Hot-smoked or gently poached salmon gives you a cold, sliceable, dill-and-mustard-friendly dish that has actually been cooked, with a target internal temperature you can probe. The texture is different and, in a good version, not worse. For anyone advised against raw fish, or anyone who cannot verify the sourcing conditions above, that is the dish to make instead. How to record the windows for those species is in the doneness windows by species.
In Plain English
What it means. Gravlax is raw fish that has been firmed and flavoured by salt. It looks cooked and it is not. Because of that, the safety of the finished dish is decided by where the fish came from and whether it has had a specified freezing treatment, both of which happen before you touch it.
Who it helps. Anyone about to follow one of the many cure recipes that mention neither sourcing nor freezing, and anyone who has assumed that a long cure makes fish safe.
When to use it. Only when you can verify the fish's parasite-control history, follow a validated gravlax recipe that supplies its own cure duration, keep the process refrigerated, and confirm that nobody eating it is in a group advised against raw fish.
What to do next. Ask the specific sourcing question before you buy anything. Get a scale, because the cure is a weight ratio and nothing else will do. Keep the whole process refrigerated. Read the current FDA Food Code parasite controls and FDA consumer seafood guidance directly. If the fish, equipment or applicable rule cannot be verified, cook the fish instead; it is a good dish either way.
Next step
Read the FDA pages linked above before you buy fish for this; they, not this page, are where the freezing parameters, the parasite guidance, the storage figures and the vulnerable-group advice live. The salt mechanism is explained in brines and cures, the cooked alternatives are in the doneness windows by species, and the rest of the work on this ingredient is collected under everything in this section.