Most food cans are made of steel coated with a thin layer of tin, though some are made of aluminum. Both types also have an invisible polymer lining on the inside that keeps the metal from reacting with the food. That three-part combination of structural metal, protective tin, and interior coating is what allows canned food to stay safe on a shelf for years.
Steel vs. Aluminum
Steel is the workhorse of the canned food world. The vast majority of cans you see in the grocery store, from beans and corn to soups and tomato sauce, use steel as their base material. This steel is coated on both sides with an extremely thin layer of tin, typically 0.0003 to 0.0008 mm thick. That tin layer prevents the steel from rusting and gives the can a smooth, food-safe surface. The industry has been pushing toward the thinner end of that range in recent years to reduce costs and material use, but even a microscopic layer of tin is enough to block corrosion.
Aluminum cans are more common in beverages (think soda and beer) but also show up in some food products, particularly pet food and certain meat products. Aluminum is lighter, easier to shape, and doesn’t rust the way bare steel would. It’s also softer, which makes it ideal for pull-tab lids and easy-open designs. Some cans are “bimetal,” using steel for the body and aluminum for the ends.
Two-Piece and Three-Piece Construction
Food cans come in two basic designs. A three-piece can has a cylindrical body formed from a flat sheet of metal, with a separate bottom and lid attached by seams. This is the traditional design, and it works especially well with steel because the material is rigid enough to hold its shape in various sizes. Three-piece cans are easy to scale up or down, which is why you see them in everything from small tomato paste cans to large institutional sizes.
A two-piece can starts as a single disc of metal that gets stamped and drawn into a cup shape, forming the body and bottom as one seamless unit. Only the lid is added separately. Fewer seams mean fewer potential weak points, which is one reason two-piece cans dominate the beverage industry. They’re particularly well suited to lightweight aluminum and its alloys. In food packaging, you’ll find two-piece cans used for products like tuna and shallow containers, though three-piece steel cans remain the standard for most shelf-stable foods.
The Coating Inside the Can
Every food can has a thin polymer coating sprayed or applied to its interior surface. This lining is arguably more important than the metal itself when it comes to food safety. Without it, acids in foods like tomatoes, citrus fruits, and pickles would slowly dissolve metal into the product. Even low-acid foods like green beans benefit from the barrier, since direct metal contact can cause off-flavors and discoloration.
The most common interior coatings include epoxy resins, polyester, acrylic, vinyl, and phenolic resins. Different foods get different coatings. White epoxy resins pigmented with aluminum work well for fruits and vegetables. Fish and meat products, which release sulfur compounds during heat processing, typically get phenolic or epoxy-phenolic blends with aluminum pigment to prevent dark staining on the can wall. Vinyl-based coatings often line soft drink cans, while a related formulation called vinyl organosol is used for fish because it offers better adhesion and corrosion resistance.
Each coating type has trade-offs. Polyester coatings are very flexible and stick well to metal, but their corrosion resistance is relatively poor, so they’re generally reserved for non-acidic foods. Vinyl coatings are flexible too, but plain vinyl has weak adhesion to metal surfaces. Epoxy resins remain popular because they combine strong adhesion, chemical resistance, and durability under the extreme heat of the canning process.
BPA and Newer Alternatives
The most widely discussed concern about can linings involves BPA (bisphenol A), a chemical building block used in traditional epoxy coatings. BPA can migrate from the lining into food in trace amounts, and its potential health effects have been debated for over a decade. The FDA’s position, based on its most recent safety assessment, is that BPA is safe at the levels currently found in canned foods. However, BPA-based materials have been removed from baby bottles, sippy cups, and infant formula packaging after manufacturers voluntarily abandoned those uses.
Regardless of the FDA’s stance, consumer pressure has pushed the industry toward alternatives. Manufacturers now use the term “BPA non-intent” (BPA-NI) for coatings designed without BPA as a starting ingredient. First-generation replacements include polyester and acrylic coatings. Oleoresins, a plant-derived option, have been rediscovered as a BPA-free choice. More advanced options are entering the market too: PET-based coatings laminated directly onto the can surface (developed in Japan), polyolefin-based coatings, and reformulated epoxy resins that don’t use BPA at all. The transition is ongoing, and many major brands now label their products as BPA-free, though the specific replacement coating varies by manufacturer and food type.
How Acidic Foods Affect the Can
Acidity is the single biggest challenge in canned food packaging. When you open a can of tomatoes, pineapple, or sauerkraut, the product inside has been sitting in contact with the can wall for months or even years. Acids in these foods can attack both the metal and the protective lining. Research on aluminum cans shows that acetic acid (the main acid in vinegar) causes a negative shift in the metal’s corrosion potential, meaning it becomes more vulnerable to dissolving. This is true even for coated cans, though the coating dramatically slows the process.
This is why coating selection matters so much. Highly acidic foods require coatings with strong chemical resistance, which is one reason epoxy-based linings have been so hard to replace. The tin layer on steel cans also plays a role here: tin is less reactive than steel in acidic environments, so it acts as a sacrificial buffer. For the most aggressive products, manufacturers may use heavier tin coatings or more chemically resistant lining formulations.
Recycling Steel and Aluminum Cans
Both steel and aluminum cans are infinitely recyclable, meaning the metal can be melted down and reformed into new products without losing quality. Steel cans have a practical advantage at recycling facilities: they’re magnetic, so they can be easily separated from other materials using magnets on the sorting line. Aluminum requires eddy current separators, which are standard at modern facilities but add a step.
The recycling rate for aluminum containers and packaging in the United States was about 35% as of 2018, according to the EPA. That figure includes beverage cans, food containers, and foil. Steel cans generally have comparable or higher recycling rates, partly because of how easily they’re captured by magnets during waste processing. The coatings and tin layer burn off or separate during the melting process, so they don’t interfere with recycling. If you’re wondering whether to rinse your cans before recycling, a quick rinse helps prevent contamination at the facility but doesn’t need to be spotless.