Why Is Fish Intended to Be Eaten Raw Frozen First?

Many fish from the sea may contain parasites, and this is not a defect related to the fish’s quality or freshness; it is a natural occurrence. Cooking removes this risk because heat inactivates parasites. If fish will be eaten raw, heat is not used, so freezing takes its place. Freezing does the same job when maintained at a sufficiently low temperature for a sufficiently long time; if either of the 2 conditions is missing, the process is not considered complete.

The 2 established schedules are alternatives: 7 days at −20°C / −4°F or 15 hours at −35°C / −31°F. These temperatures refer to the center of the fish that must reach the target; the freezer air being at that temperature is not enough on its own—the entire product must reach it. The holding time starts after that point is reached. Commercial facilities can apply these schedules reliably with their equipment. These 2 schedules take the place of cooking, not freshness; being frozen does not mean the fish was not fresh.

Home freezers generally operate around −18°C / 0°F, and this temperature meets neither of the 2 schedules above. In addition, the temperature in a home freezer is not constant: it rises each time the door is opened, newly added food warms the interior, and the appliance’s own cycle causes fluctuations. The actual temperature reached at the center of the product cannot be measured either. For these reasons, a home freezer does not guarantee this process, and it is important to understand that it cannot guarantee it. Even if you place a thermometer inside the freezer, it measures the air temperature, not the temperature at the center of the fish.

If fish will be eaten raw, the approach is clear: buy it from a seller who states that the product was prepared for this purpose. This information should appear on the label or in the seller’s statement, and you should ask directly. Once the product is brought home, maintain the cold chain; thaw it in the refrigerator in a covered container on the lowest shelf, and consume it the same day. Do not eat fish raw if its source is uncertain; cook it instead, and nothing is lost by doing so.

Cooking is always the simplest and most certain method. Fish is considered safe when it reaches 63°C / 145°F, a temperature that a thin fillet reaches within minutes. Marinating fish in lemon juice is not a substitute for cooking; the acid changes the color and texture of the flesh but does not do what heat does. Salting and smoking alone do not provide the same assurance either. In short, the decision to eat fish raw depends on knowing where it came from.