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Canned tuna, a staple in millions of kitchens around the world, was first manufactured in 1904 by Albert P. Halfhill in California. It has since become a reliable source of protein and omega-3 fatty acids for people around the world. Canned tuna production process consists of multiple stages including thawing, cutting, steaming, deboning and sterilizing, all of which ensure the product quality and long shelf life.

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The basics of canned tuna production process – which tuna is used for canning?

Although five different tuna species are used for commercial purposes, only three are used for canning- skipjack, yellowfin, and albacore. The canned tuna classified as light meat tuna comes from skipjack and yellowfin, while white meat tuna comes from albacore. The two differ in omega-3 content, color and taste. Light meat tuna is darker, lower in fat and omega-3s and more flavorful, while white meat tuna is lighter, with a firmer texture and high in omega-3 fatty acids.

The canned tuna production process begins with the frozen tuna arriving from the fisheries at the processing plant. There, the tuna is thawed in large water tanks, sized and sorted to minimize the weight loss from overcooking. The sorted tuna is then cut and subsequently steamed in large pressure-cooking chambers. This initial pre-cooking removes excess oils and makes it easier to separate the fillets from the rest of the meat.

Canning and sterilizing tuna: the crucial steps

After the initial steaming, the meat is cooled down and deboned, separating the loins from the bones and the skin. Then, the meat is transferred into cans by a filling machine. Manufacturers can add salt, water, oil, or marinade to the can, then hermetically sealed.

The filled cans are then cooked and sterilized at a temperature of 121°C for 20 minutes to eliminate harmful microorganisms but still retain tuna’s nutrients.

Sterilization is crucial for canned tuna production. Canned tuna is a low acid food, which supports the growth of microorganisms such as Clostridium botulinum. Clostridium botulinum is found in the intestines of fish, animals, birds, insects and the soil.

Being a heat-tolerant microorganism, it can produce a neurotoxin if the canned fish is underprocessed. Spores, if present in unprocessed canned tuna or if they enter the can after processing, can create issues. The processing time depends on the can size.

Mercury in canned tuna - How much of it is allowed?

Another hazard with seafood consumption is mercury poisoning. Mercury is naturally present in seafood, most often in sharks, swordfish, bluefin, and albacore tuna. Of the two tuna species used for canning, albacore contains more mercury than skipjack due to its larger size; however, both species are considered to have low mercury content.

Canned white albacore tuna typically contains about 0.32 parts per million of mercury. Canned light tuna contains about 0.12 parts per million of mercury. The FDA and the EU allow products that contain 1 part of mercury per million, and have recommended intakes of tuna for children and adults.

Environmental impact of tuna production process

With the increasing public outcry for environmentalist policies and practices, the canned tuna production process has adapted well. A study by The Environmental Working Group determined that canned tuna production produces 6.1 kg of CO2 a day, which is lower than any other meat industry. Most of the produced carbon, 68% total, comes from the fuel used for fishing, while the rest is attributed to subsequent transportation, factory processing and storing.

The way tuna is fished also contributes to the industry’s carbon footprint. With purse seine fishing, the fisheries use a cylindrical net that surrounds a school of tuna and closes the bottom. Purse seine fishing has the lowest carbon footprint per kilogram of caught fish. This fishing technique’s efficiency could potentially lower the number of fishing boats and the fuel needed to support larger fleets.

Tuna waste repurposed: byproduct to pet food

To reduce waste, tuna canning industry repurposes the remaining byproduct. The cannery produces 50 to 70% of solid waste after tuna processing, including heads, guts, gills, red tuna meat, and bones that must be discarded or repurposed.

Only white tuna meat, or loins, is used for human consumption and the remaining red meat is separated and used for animal or pet food. Sometimes, even the other discarded parts of tuna, such as the skin, fat, and organs, are added to pet food, which is especially beneficial for cats in moderation as it is a source of protein, omega-3s, and low-carb.

Moreover, the leftover meat, bones and skin from the tuna canning process can be used to produce fish oil, fish meal, gelatin and fertilizer, which significantly minimizes the amount of waste.