Metal Packaging for Fish Products: Benefits and Risks

Metal packaging has been a cornerstone of the fish processing industry for over two centuries. From the earliest tinplate cans of the 1800s to today’s advanced aluminum containers, metal remains one of the most trusted materials for preserving seafood. But while metal cans offer exceptional protection and shelf life, they also carry certain risks – particularly related to the migration of metals like tin and lead into the food. Understanding both the benefits and hazards of metal packaging is essential for anyone working in fish processing, food safety, or product development.

A brief history of metal packaging in the fish industry 🔗

The concept of metal canning dates back to the early 19th century, when the need to preserve food for military use drove innovation in packaging. By the mid-1800s, commercial canning had become widespread, and tinplate steel – steel coated with a thin layer of tin – emerged as the dominant packaging material . Over time, aluminum entered the picture as a lighter, corrosion-resistant alternative. Today, the fish canning industry relies primarily on tinplate cans and aluminum cans, with tin-free steel (TFS) also gaining traction as a cost-effective option.

Various fish products such as mackerel, mussels, fish curry, tuna, and prawns have been successfully canned in polymer-coated tin-free steel containers, achieving shelf lives exceeding 24 months at ambient temperatures . This demonstrates just how effective metal packaging has become at preserving seafood quality over extended periods.

Types of metal packaging used for fish products 🔗

Tinplate cans 🔗

Tinplate is steel that has been coated with a thin layer of tin, typically applied through electroplating . The steel provides structural strength, while the tin layer protects against corrosion and prevents rust from reaching the food inside. Tinplate cans are especially popular for fish packed in oil or brine because they hold up well during high-temperature retort sterilisation. Modern tinplate cans often include an additional internal polymer coating (lacquer) that further reduces metal-food contact.

Tin coating thickness typically ranges from 2.8 to 11.2 grams per square metre, depending on the product’s requirements. These specifications directly impact how well the can protects against oxidation and preserves the nutritional quality of fish – particularly the omega-3 fatty acids that are highly sensitive to air and light exposure.

Aluminum cans 🔗

Aluminum cans are made from high-purity aluminum alloys and are valued for their lightweight nature, excellent malleability, and natural corrosion resistance. Unlike steel, aluminum is lighter and generally offers better corrosion resistance, which also makes it less expensive to transport . Aluminum is widely used for premium canned fish products and easy-open container formats. Its recyclability is another major advantage – aluminum cans can be recycled indefinitely without losing their material properties.

Tin-free steel (TFS) 🔗

TFS cans use a chromium plating instead of tin. This involves electroplating steel sheets with a thin layer of metallic chromium, followed by a chromium oxide layer . TFS is a more affordable alternative to tinplate and works well for products that don’t require the premium corrosion resistance of tin-coated steel. It’s commonly paired with internal lacquers to ensure adequate food protection.

Key benefits of metal packaging for fish products 🔗

Superior barrier properties 🔗

Steel and aluminium packaging offer complete protection against light, water, and air, and metal cans without resealable closures are among the most tamper-evident packaging materials available . For fish products, this is critical. Omega-3 fatty acids in fish are highly susceptible to oxidation when exposed to air and light, and metal packaging effectively blocks these degradation factors.

Extended shelf life 🔗

Properly processed canned fish can remain safe and retain quality for two to five years under appropriate storage conditions. Food and drink packed in steel cans maintains vitamin content comparable to freshly prepared food, without the need for preserving agents . This long shelf life also makes it feasible to distribute nutritious seafood to landlocked regions far from coastal areas.

Durability and convenience 🔗

Metal cans withstand significant physical stress during transportation and handling. As an ambient packaging medium, steel cans do not require cooling in the supply chain, which simplifies logistics and storage while saving energy and cost . Additionally, modern innovations like easy-open ends and peel-off lids add consumer convenience without compromising the integrity of the seal.

Sustainability and recyclability 🔗

Steel cans are considered strong ecological performers because they can always be recycled, and the steel industry actively uses recycled cans in the production of new steel products . Aluminum, similarly, is infinitely recyclable. The global average recycling rate for metal packaging is around 60-70%, making it one of the more sustainable packaging options available.

Risks associated with metal packaging 🔗

Despite its many advantages, metal packaging does carry risks – primarily related to the migration of metals and other chemicals from the can into the food product. Understanding these risks is vital for ensuring consumer safety.

Tin migration 🔗

When the internal coating of a tinplate can is damaged or insufficient, tin can dissolve into the food over time. This process is known as tin migration, and it is accelerated by factors like high acidity, elevated storage temperatures, and prolonged storage duration. Inorganic tin is commonly present in food-grade can coatings and can leach into acidic foods during prolonged storage .

Acute tin ingestion at high levels can cause gastrointestinal disturbances including nausea, vomiting, diarrhoea, and abdominal cramps. Chronic low-level exposure may also interfere with the absorption of essential minerals like zinc and copper. Elevated exposure to tin and its compounds has been linked to neurological and gastrointestinal problems . However, studies have found that tin levels in modern canned products are typically far below the maximum regulatory limits, suggesting minimal transfer from the packaging .

Lead contamination 🔗

Lead is a far more dangerous contaminant. Historically, lead solder was used to seal cans, which introduced significant amounts of lead into canned food. Early cans were often soldered with high-lead solders , though modern manufacturing has largely eliminated this practice. Today, lead may still enter canned fish at trace levels through raw material impurities or environmental contamination of the fish itself.

Lead primarily affects the brain and nervous system, especially in children, and long-term exposure can damage the kidneys, digestive system, and reproductive organs . Lead and cadmium toxicity can result in renal, cardiovascular, and reproductive issues , making strict control of lead levels in packaging materials essential.

Bisphenol A (BPA) from internal coatings 🔗

Many metal cans use internal epoxy coatings derived from bisphenol A (BPA) to prevent direct metal-food contact. However, BPA is an industrial chemical used in the production of epoxy resins that serve as protective can coatings for food applications . BPA is classified as an endocrine disruptor, meaning it can interfere with the body’s hormonal system. Researchers have found that the transfer of substances from can linings into food increases significantly with heat, and that their bioaccessibility is higher when ingested with fatty foods .

This is particularly relevant for canned fish, which is often packed in oil – a medium that can facilitate greater chemical migration from coatings into the product.

Strategies to mitigate metal packaging risks 🔗

Internal lacquers and coatings 🔗

The most effective strategy for preventing metal migration is the application of internal lacquers on the can surface. These coatings create a physical barrier between the metal and the food. Health and product safety concerns of metal packaging include migration of BPA, lead, cadmium, mercury, aluminium, iron, nickel, and tin dissolution – metals are not inert to food products and are therefore coated with protective lacquers to prevent metal-food interaction . Modern lacquers include epoxy-phenolic, polyester, and organosol coatings, each suited to different food types and processing conditions.

Advanced internal lacquers enhance corrosion resistance and prevent metallic taste migration, which is crucial given the sensitivity of seafood products . Quality control during manufacturing includes porosity checks and coating thickness testing to ensure no weak spots exist where metal could leach through.

Proper canning methods 🔗

Good manufacturing practices (GMP) play a key role in minimising risks. Correct retort processing temperatures and times must be maintained to ensure commercial sterility without overheating, which could damage internal coatings. Double-seam integrity must be verified to maintain the hermetic seal, and proper cooling procedures after retorting help prevent coating degradation.

Controlled storage conditions 🔗

Storing canned fish products at moderate temperatures (below 25°C) and away from direct heat helps slow down the rate of metal migration. Proper inventory rotation – using a first-in, first-out (FIFO) system – ensures that older stock is consumed within its recommended shelf life. This is important because migration rates increase over time, even in well-coated cans.

Use of BPA-free coatings 🔗

In response to health concerns, the industry is increasingly shifting towards BPA-free alternatives such as polyester-based and acrylic coatings. These newer formulations aim to provide the same level of food protection without the endocrine-disrupting risks associated with BPA. The European Commission has set a specific migration limit for BPA at 0.05 mg/kg of food , and many manufacturers now pursue BPA-free certification as a market differentiator.

Regulatory standards for metal packaging safety 🔗

Governments and international bodies have established stringent regulatory frameworks to control metal levels in canned food and ensure consumer safety.

International standards 🔗

The Codex Alimentarius, published jointly by the FAO and WHO, sets international maximum levels for contaminants in food, including tin in canned products (generally 250 mg/kg for most canned foods). To safeguard human health, regulatory agencies worldwide have established limits for toxic element contamination in seafood . The European Food Safety Authority (EFSA) has established a tolerable weekly intake of 14 mg/kg body weight for tin.

National regulations 🔗

The US FDA regulates tin levels in canned food and sets maximum allowable limits for lead in packaging materials. The European Union enforces strict BPA migration limits and requires that all food-contact materials undergo rigorous safety testing before approval. In India, the Food Safety and Standards Authority of India (FSSAI) aligns its standards with Codex recommendations and mandates testing of metal levels in canned food products.

Overall, concentrations of aluminium, cadmium, mercury, and tin in canned fish across various studies have been found below the maximum permissible limits – which is reassuring, but ongoing monitoring remains critical as production scales up globally.

Testing and compliance 🔗

Manufacturers are required to conduct regular testing of their packaging materials. Assessment methods include inductively coupled plasma-optical emission spectroscopy (ICP-OES) and other analytical techniques that allow accurate detection of metal contaminants in canned foods . These tests evaluate both the coating integrity and the actual levels of metals that migrate into food under simulated storage conditions.

The future of metal packaging in the fish industry 🔗

The fish canning industry is evolving rapidly. Lighter-gauge metals, improved coating technologies, and smarter manufacturing processes are making metal packaging safer and more sustainable than ever. Advanced manufacturing techniques now allow for lighter-weight cans without compromising structural strength, reducing material use and shipping costs .

Research into nano-coatings and bio-based lacquers promises even better barrier properties with lower environmental and health impacts. Meanwhile, the push for circular economies has reinforced metal’s position as a highly recyclable and environmentally responsible packaging choice. As consumer awareness about food safety grows, the industry will need to continue investing in innovation while maintaining rigorous adherence to regulatory standards.

What do you think? Given the health risks associated with metal migration, should the fish industry accelerate its shift towards BPA-free and advanced coating technologies – or are current regulatory limits sufficient to protect consumers? How might the growing demand for sustainable packaging influence the future of metal cans in fish processing?

References

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC7270472/
2. https://www.triviumpackaging.com/products/industry/food/sea-food
3. https://pmc.ncbi.nlm.nih.gov/articles/PMC7511825/
4. https://www.fao.org/fao-who-codexalimentarius/codex-texts/all-standards/en/