What Exactly Is Canned Tuna, and How Is It Shelf-Stable?
If the thought of eating unrefrigerated fish that’s been sitting on a grocery store shelf for days (or even weeks) sounds, frankly, horrible, you’re not alone.
But that’s exactly what canned tuna is—fish stuffed in a small steel or aluminum container, sold in dry goods aisles. It’s also edible, according to the expiration date, for several years after its packing date. How is this possible? And how is this possibly good for you?
Here, several experts break down the process, sharing where canned tuna comes from, what makes it shelf stable and safe to eat, and how it compares, nutrition-wise, to fresh tuna.
The Fishing Process
Canned tuna originates from the same source as fresh tuna—with real tuna.
Much of the canned tuna that you’ll find in your grocery store shelves comes from the Pacific Ocean. The tuna in StarKist cans, for example, originates primarily from the western tropical Pacific Ocean, says Laura Ali, registered dietitian and senior manager of nutrition and regulatory affairs at StarKist. Wild Planet, another canned tuna brand, sources tuna from sustainable fisheries in the North Pacific, Central Pacific and coastal New Zealand, says Sue Jacobs, director of Marketing at Wild Planet.
StarKist tuna is caught and then frozen on the fishing boats as quickly as possible—either with blast freezing (i.e. being placed in a large freezer), or with brine freezing (i.e. being placed in a chilled salt water brine). Tuna in Wild Planet cans is frozen on the boats as well.
The Production Process
After being caught and frozen, the fish is taken back to port and transported to the plant, where it’s stored in freezers until ready for production, which is “usually a pretty quick turnaround,” says Ali. Then, it’s thawed, inspected and cleaned and any tuna that doesn’t meet quality specifications is removed. At StarKist, the fish that pass the test are then cooked in large steamer baskets and loined. The loins are then cleaned, the skin and bones are removed, and the meat is chunked or sliced (depending on the variety being produced) and placed in a can or pouch.
Wild Planet, on the other hand, skins and hand cuts the still-frozen tuna and places it into cans. The fact that frozen tuna is placed in the cans (versus already cooked tuna, as is the standard with many canned tuna brands), means the tuna is only cooked once, and not twice. This minimal cooking helps the tuna retain more of its natural flavor and nutrients, says Jacobs, since the cooking process in general—whether with fish, meat or produce—causes some leakage of nutrients and flavor.
The final step at StarKist: liquid is added (either water, vegetable broth, or oil) to the can. “There is nothing extra placed in with the tuna that would preserve it,” says Ali, using chemical preservatives as an example. “What preserves it is the processing method.”
At Wild Planet, the tuna is either salted, or put in the can just by itself.
From there, the cans are placed in a special cooker that heats the cans to a high temperature very quickly under pressure. Through this process, the tuna is vacuum sealed and sterilized in the cans so that it’s shelf stable and safe to eat. “It’s the same process as if you were processing fruits and veggies,” says Ali. “No preservatives are added—it’s just the processing.”
Once the sterilization process is complete, the cans are good to go. StarKist cans have a shelf life of 4 years, and Wild Planet cans are good for 3 years.
The Nutrition Profile of Canned Tuna
Tuna, in general, is a great source of many nutrients, including protein, selenium, and Vitamin D, says Lauren Manaker, a South Carolina-based registered dietitian. You’ll get these nutrients whether you eat your tuna fresh, or from a can, although fresh tuna will have slightly higher concentrations of these nutrients since its typically less processed (just like fresh fruits and vegetables are more nutritious than their canned counterparts).
Tuna is also especially great for new moms and moms-to-be. “Tuna canned in oil typically contains 17 mcg of iodine, which is a key nutrient when pregnant and lactating,” says Manaker.
That’s not all. Canned tuna is “an easy way to eat omega-3s, especially EPA and DHA, which are important for heart, brain, and eye health,” says Tori Schmitt, registered dietitian nutritionist and founder of YES! Nutrition.
That said, a common fear with fish consumption, says Schmitt, is high mercury content. Before you freak, know this: “Mercury ‘biomagnifies’ as we go up the food chain,” explains Schmitt, “which means that bigger fish (compared to the smaller fish) often contain higher levels of mercury.”
To keep your mercury intake in check, opt for smaller tuna fish—like light or skipjack tuna—over arger fish, like albacore, yellowfin/ahi, and bigeye tuna.
How Much Canned Tuna Should I Eat a Week?
FDA guidelines recommend 2 to 3 four-ounce servings of seafood a week, from “a variety of cooked fish.” Because of the mercury concerns noted above, the FDA recommends limiting albacore tuna to one four-ounce serving a week, says Manaker.
As for light or skipjack tuna, “I recommend keeping consumption to no more than two servings per week,” Schmitt. “That means that other fish full of omega-3s, like salmon or sardines, can fit into the eating pattern as well.”
What to Look for in a Can
It pays to pay attention to the overall quality of the can that tuna is stored in, says Manaker. One watch-out: cans that may contain BPA, an industrial chemical used as protective lining in some food and beverage cans that in recent years, has been linked to negative health effects. Look for cans that say “BPA-free” on the label.
Another tip: avoiding cans with dents, discoloration, cracking or bulging. “It is rare, but if the can is compromised in any way, it is best to avoid,” says New York-based registered dietitian Jackie Arnett Elnahar. “Overall, you want to also store the can in a cool, dry place to avoid affecting the integrity of the can.
The Bottom Line
Thanks to the specialized production process, canned tuna is totally safe to eat—in moderation, that is. “Canned tuna is a great protein source that is great to keep on-hand,” says Manaker, “and I am always a fan of people incorporating seafood into their diet safely for a number of health reasons.”