Frozen fish: pollock, cod, herring

Frozen fish is one of the most widely available and affordable sources of animal protein in the diet of many populations. Pollock, cod and herring occupy leading positions in the global catch and consumption structure due to their nutritional value, wide habitat and relative ease of industrial processing. Freezing is the main method of fish preservation, allowing its properties to be maintained over a long period and ensuring stable supplies regardless of the fishing season.

Chemical Composition and Nutritional Value

The flesh of pollock, cod and herring is characterised by a high content of complete protein, including all essential amino acids. Protein content ranges from 15 to 19% depending on the species and fishing season. Fat content varies significantly: cod and pollock are lean fish (fat content in the flesh usually does not exceed 1–2%), while herring, especially in the autumn-winter period, accumulates a significant amount of fat (up to 15–20% and more), rich in omega-3 polyunsaturated fatty acids. The flesh also contains B vitamins, vitamins A and D (especially in cod liver), phosphorus, iodine, selenium and other trace elements. It is this combination of affordable price, high protein content and beneficial fats that makes this group of fish a staple of mass nutrition.

Classification, Standards and Grades

In Russia and the EAEU countries, requirements for frozen fish are regulated by a system of state standards. The main document for a long time was GOST 32366-2013 "Frozen fish. Specifications", which applies to frozen fish of all families and species. The standard establishes requirements for quality, cutting, glazing, packaging, labelling, acceptance and storage. From mid-2026, an updated GOST 35273-2025 comes into force, consolidating previous standards and tightening quality requirements, including criteria for raw materials, cutting and shelf life.

In addition to the general standard, specialised documents apply to certain species. Requirements for frozen herring and some other fish species are established by separate standards that were previously distinguished from the general GOST. For products supplied for export, the requirements of the importing country are additionally taken into account.

By quality, frozen fish is divided into first and second grades (in some standards — categories). The grade is determined by a combination of organoleptic and physicochemical indicators:

• First grade: fish surface clean, of natural colour, without damage; after thawing, the flesh consistency is dense and elastic; the odour is characteristic of fresh fish of the given species, without foreign notes.

• Second grade: minor damage to the skin is allowed, a dull surface, a softer consistency after thawing, a weakened but not putrid odour; minor bruises and subcutaneous yellowing not associated with fat oxidation are allowed.

Grading also depends on the type of cutting: whole (ungutted), gutted with head, gutted headless, fillet, piece, carcass, back and other types. Signs of repeated freezing, as well as foreign odours and tastes, are not allowed.

Freezing and Glazing Technology

The quality of frozen fish directly depends on the freezing rate and storage conditions. Rapid freezing forms small ice crystals in the flesh that do not damage cellular structures, preserving juiciness and texture after thawing. The temperature in the fish body upon discharge from freezing units must be no higher than minus 18 °C for artificial freezing. Slow freezing leads to the formation of large crystals that injure muscle fibres and cause quality loss.

To protect against drying, fat oxidation and the penetration of foreign odours, fish is coated with glaze — a thin ice crust formed by repeated immersion in water or spraying. The glaze must evenly cover the surface of the fish or block and must not detach upon light tapping.

Glaze content standards are differentiated. Upon release from fish processing vessels or production cold stores, the glaze mass must be at least 4% relative to the mass of glazed fish or block. At the same time, for frozen fish products in consumer packaging, the glaze mass must not exceed 5%, so as not to mislead the consumer about the actual product weight. Herring is produced only in glazed form, with a glaze mass fraction of at least 4% of the fish weight. Instead of glazing, protective coatings based on polyvinyl alcohol or vacuum packaging are permitted.

Characteristics of Individual Species

Pollock (Theragra chalcogramma) is the most abundant fishery object in the North Pacific. Pollock flesh is lean, white, with a neutral taste, making it a versatile raw material for the production of fillets, minced fish, imitation products and culinary items. Frozen pollock is supplied as whole fish, gutted headless carcass, fillet and back. Blocks of headless pollock and back-cut pollock must be glazed or wrapped in anti-adhesive paper.

Cod (Gadus) is a valuable commercial species inhabiting the North Atlantic and the North Pacific. Cod flesh is distinguished by low fat content, high protein content and an easily digestible consistency. Frozen cod is supplied as carcass, fillet with and without skin, and pieces. Due to its dense flesh structure, cod tolerates freezing well and is widely used in dietary and baby food.

Herring (Clupea) is a mass commercial fish of the North Atlantic and Pacific Ocean, characterised by high fat content in certain seasons. Frozen herring is used for subsequent processing (salting, smoking, preserves) and is sold whole or as a carcass. Herring is produced only glazed, which is due to its high fat content and tendency to oxidise upon contact with air.

Safety and Storage

Frozen fish is a perishable product, so maintaining the temperature regime at all stages — from freezing to sale — is critically important. Storage is carried out at a temperature not higher than minus 18 °C. Recommended shelf lives depend on the fish species, cutting method and storage temperature: on average they range from 3 to 10 months at minus 18 °C and can be extended at lower temperatures. Specific periods are set by the manufacturer with an indication of storage conditions.

Re-freezing of fish is not allowed, as it leads to loss of cellular juice, deterioration of texture and accumulation of fat oxidation products. Signs of re-freezing include a dull surface, dry consistency, a large amount of released water after thawing and a foreign odour. To prevent spoilage, product proximity must be observed and fish must not be stored next to strong-smelling products.

Market and Trends

The global frozen fish market demonstrates steady dynamics, supported by demand for affordable protein and the development of logistics chains. Russia is one of the largest suppliers of frozen fish to the world market, primarily to China. The export structure is dominated by frozen pollock, cod and herring. There is steady growth in supplies: exports of frozen pollock to China increase by 15–25% per year, cod — by 21–25%, ungutted herring — by 30–45% depending on the period.

Key industry trends include: tightening requirements for product quality and safety (including within the new GOST), development of deep processing (fillet, minced fish, semi-finished products), and growing demand for value-added products. China remains the largest buyer of Russian fish products, making it a strategic partner for exporters. Producers with access to quality raw materials, modern freezing capacities and logistics occupy stable competitive positions.

Conclusion

Frozen fish (pollock, cod, herring) remains a fundamental product of mass nutrition and an important item of international trade. Understanding quality standards (GOST 32366-2013 and the incoming GOST 35273-2025), requirements for glaze and grading, as well as storage conditions, is the basis for competent product selection and the organisation of stable supplies. Selecting the type and grade of fish for specific purposes — from retail sale to industrial processing — requires an individual approach.