Choosing the Right Tin Containers for Canning

Tin containers are the backbone of the food canning industry. Whether it’s canned peaches sitting on a supermarket shelf or bulk tomato sauce in a commercial kitchen, the container holding that food is doing a lot more than just being a metal box. It’s engineered to protect the food from spoilage, corrosion, and chemical reactions – sometimes for years at a time. Understanding the types of tin containers, their internal coatings, and their standard sizes is essential knowledge for anyone working in food processing.

What are tin containers made of? 🔗

Despite the name, tin containers are not made entirely of tin. The base material is low carbon steel, selected for its strength, durability, and ability to be formed into different shapes. This steel base gives the container the structural integrity needed to handle the high temperatures and pressures of commercial canning processes – including sterilisation, pasteurisation, and vacuum sealing.

The steel is then coated with a thin layer of tin metal through a process called electroplating, producing what the industry calls tinplate. This tin coating serves as a protective barrier between the steel and the food inside. Without it, the steel would rapidly corrode when exposed to the moisture, acids, and other compounds found in most foods. According to research published in Food and Chemical Toxicology, roughly one-third of the world’s total tin production goes into manufacturing tinplate, with food packaging being its largest application.

Tin is non-toxic, chemically stable, and resistant to rust – even in humid environments. It also helps create a hermetic (airtight) seal, which is fundamental to the entire principle of canning. The combination of a strong steel core and a corrosion-resistant tin surface is what makes these containers suitable for storing food safely over extended periods.

Why are tin containers lacquered? 🔗

While the tin coating provides a solid first line of defence, it is not always sufficient. Many foods contain compounds that can still react with tin or the underlying steel, leading to problems like off-flavours, discolouration, or even container failure. This is why manufacturers apply lacquers – specialised protective coatings – to the interior and sometimes the exterior of tin containers.

Lacquers act as an additional chemical barrier between the metal and the food. They are applied as thin, uniform layers and then cured at high temperatures (typically around 200-210°C) to form a durable film. As noted by ILSI Europe’s report on metal packaging, internal coatings protect the food from picking up metallic tastes and protect the metal from being corroded by the food contents.

Without proper lacquering, storing acidic foods like citrus juice or tomato-based products directly against the metal could cause the tin layer to dissolve. Similarly, protein-rich foods containing sulfur compounds could react with the metal and create unsightly black stains inside the can. Lacquering addresses both problems.

External lacquering 🔗

It’s worth noting that lacquering isn’t limited to the inside. External lacquers protect the can from atmospheric corrosion during storage, transport, and display. They also provide a smooth surface for labelling, printing, and decoration.

Types of lacquers used in tin containers 🔗

Not all lacquers are the same. The type of lacquer used depends entirely on the nature of the food being packed. The Comprehensive Reviews in Food Science and Food Safety journal identifies several lacquer types based on their chemical composition and intended use. For the canning of fruits and vegetables, two types of lacquers are most important.

Acid-resistant lacquers 🔗

Acid-resistant lacquers are designed for foods with high acidity – typically those with a pH between 2.5 and 4.5. This category includes most fruits (like peaches, pineapples, and citrus), tomato products, pickled vegetables, and fruit juices.

When acidic food comes into prolonged contact with tin, it can dissolve the tin coating, potentially causing metallic flavours and increasing the tin content in the food. Acid-resistant lacquers – most commonly based on epoxy-phenolic formulations – create a chemically inert barrier that withstands these low-pH conditions throughout the product’s shelf life.

An interesting exception exists for some clear-juiced fruits like pears and peaches. According to the ILSI Europe report, these are sometimes packed in cans with unlacquered bodies but lacquered ends, because a small amount of tin dissolution actually helps preserve the colour and flavour of these particular products. Fully lacquered containers for such fruits can sometimes cause the covering liquid to become cloudy.

Sulfur-resistant lacquers 🔗

Sulfur-resistant lacquers are used for foods that contain sulfur-bearing amino acids or other sulfur compounds. Common examples include corn, peas, beans, lima beans, meat, fish, shellfish, and certain other protein-rich vegetables.

During the heat sterilisation process, these foods release hydrogen sulfide and other sulfur compounds. If these compounds come into contact with the tin or iron in the container, they form tin sulfide or iron sulfide – dark-coloured deposits that create an unpleasant blackened appearance inside the can. While this discolouration (known as sulfide staining) is generally harmless to health, it negatively affects the product’s visual appeal.

Sulfur-resistant lacquers often use phenolic-based formulations, which have low permeability to sulfide ions. Another common approach is to incorporate aluminium pigment into epoxy-phenolic lacquers. The aluminium pigment masks any sulfur staining that may still occur on the tinplate surface, keeping the interior of the can looking clean when opened. Indian food safety regulations specifically require that cans for certain meat products be internally lacquered with sulfur-resistant coatings that are not soluble in fat or brine.

Other lacquer types 🔗

Beyond acid-resistant and sulfur-resistant formulations, the industry also uses general-purpose lacquers for foods that are neither strongly acidic nor sulfur-rich. Additionally, modern lacquer technology has evolved significantly in response to health concerns about bisphenol A (BPA), a compound traditionally found in epoxy-based coatings. Leading coating manufacturers like PPG and AkzoNobel now offer BPA-free (or BPA-NI, meaning non-intentional) alternatives using polyester, acrylic, and modified epoxy formulations.

Two-piece and three-piece tin containers 🔗

From a construction standpoint, tin containers are manufactured in two main configurations, and understanding the difference matters for both food processors and packaging engineers.

Two-piece cans 🔗

A two-piece can consists of just two components: a seamless body-with-bottom (formed from a single piece of metal) and a separate lid. The body is created through a process called metal drawing, where a flat disc of tinplate is pressed and stretched into a cylindrical shape. Two-piece cans have fewer seams, which reduces the risk of leaks and contamination. They are commonly used for beverages, tuna, sardines, and ready-meal products.

Three-piece cans 🔗

A three-piece can is the more traditional design, made up of a cylindrical body, a bottom lid, and a top lid. The body is formed from a rectangular sheet of metal rolled into a cylinder and closed with a welded or soldered side seam. The bottom is attached during manufacturing, and the top is seamed on after the can is filled. Three-piece cans are widely used for vegetables, fruits, soups, and other processed foods because they can be made in a greater variety of sizes relatively easily.

Standard commercial can sizes 🔗

The food canning industry uses a standardised system for designating can sizes, which ensures consistency across manufacturers, filling operations, and retail distribution. Knowing these sizes is essential for food processors to select the right container for their product and production line.

How can sizes are coded 🔗

In the American system, cylindrical can dimensions are expressed using two three-digit numbers – the first for diameter and the second for height. Within each number, the first digit represents whole inches, and the remaining two digits represent sixteenths of an inch. So a can labelled 303 × 406 has a diameter of 3 and 3/16 inches and a height of 4 and 6/16 inches. This coding system has been in use since at least the 1870s.

Common can sizes and their capacities 🔗

Here are the most widely used commercial can sizes in the food industry:

No. 1 can (Picnic can): This smaller container has a diameter of approximately 2.75 inches and a height of 4 inches. It holds about 10-12 ounces (roughly 1⅓ cups) and is ideal for single servings, tomato paste, fish products, or specialty items.

No. 2 can: One of the most common retail sizes, measuring about 3.25 inches in diameter and 4.5 inches in height. It holds approximately 20 ounces (2½ cups) and is the standard for canned vegetables, beans, fruits, and soups found in grocery stores.

No. 2½ can: A larger family-sized option, roughly 4 inches in diameter and 4.75 inches tall. It holds about 28-29 ounces (3½ cups) and is frequently used for sliced fruits, whole tomatoes, and pie fillings.

No. 3 Cylinder: This tall, narrow can holds approximately 46 ounces (about 4 cups). It is often used for large-format fruit juices – apple, tomato, and pineapple juice – in both retail and commercial settings.

No. 5 can: With a diameter of about 5⅛ inches and height of 5⅞ inches, this can holds 56 ounces (7 cups). It’s used in commercial kitchens for soups, chili, and bulk sauces consumed in a single service period.

No. 10 can: The standard institutional and food-service can, measuring approximately 6 3/16 inches in diameter and 7 inches in height. It holds 96-109 ounces (roughly 12-13 cups or 6-7 pounds of food). Restaurants, schools, hospitals, and catering operations rely on this size for bulk vegetables, sauces, beans, and fruits. It offers the best cost-per-ounce ratio among all standard sizes.

In addition to these numbered designations, cans are also referred to by their three-digit dimension codes. For example, the #300 can (approximately 3 inches in diameter) holds 14-16 ounces, and the #303 can (3 3/16 inches in diameter) holds 16-17 ounces. These sizes are standard for condensed soups, diced tomatoes, and single-recipe-sized beans.

Choosing the right container for different foods 🔗

Selecting the appropriate tin container isn’t just about picking a size – it requires matching the container’s coating to the food’s chemistry. Here’s a quick guide:

High-acid fruits (citrus, berries, pineapple, tomatoes): Use acid-resistant lacquered containers to prevent tin dissolution and metallic off-flavours.

White fruits with clear juice (pears, peaches, mushrooms): These may sometimes be packed in plain (unlacquered) tinplate bodies with lacquered ends, as slight tin dissolution can help maintain colour and flavour.

Sulfur-containing vegetables (corn, peas, beans, asparagus): Require sulfur-resistant lacquered containers to prevent dark sulfide staining during sterilisation.

Meat, fish, and shellfish: These protein-rich foods also release sulfur compounds during processing and need sulfur-resistant or phenolic-based lacquered cans.

Neutral or mildly acidic products (soups, gravies, sauces): General-purpose lacquered containers are usually sufficient.

Getting this match wrong can lead to visual defects, flavour changes, accelerated corrosion, or reduced shelf life – all of which translate to product losses and consumer complaints.

Quality and safety standards 🔗

Tin containers used for food must meet strict safety standards. Internationally, organisations like Codex Alimentarius set permissible limits for tin content in canned foods – typically 250 mg/kg for solid foods and 150 mg/kg for beverages. In the UK, the regulatory limit is 200 mg/kg. The use of fully lacquered cans for acidic foods has been largely credited with keeping tin levels well within these safety limits across the vast majority of commercially available canned products.

Lacquers themselves must be chemically inert, resistant to thermal and mechanical stress, and must adhere completely to the tinplate surface. Any defect in the lacquer coating – a scratch, a bubble, or an uncovered spot – can become a point of corrosion, potentially compromising food safety.

The environmental advantage 🔗

Tin containers are 100% recyclable, and unlike many plastics, steel and tin retain their material properties through multiple recycling cycles. This makes them one of the more sustainable choices in food packaging. The global canning industry produces approximately 80 billion food cans per year, and the recycling rate for steel cans continues to climb in most markets.

What do you think? Given the different lacquer requirements for acidic fruits versus sulfur-rich vegetables, how important is it for small-scale food processors to understand container chemistry before starting a canning operation? And could emerging BPA-free coatings change the way we think about the safety of canned food in the future?

References

1. https://en.wikipedia.org/wiki/Canning
2. https://www.sciencedirect.com/science/article/abs/pii/S0278691503002175
3. https://www.pac.gr/bcm/uploads/7-metal-packaging-for-foodstuffs.pdf
4. https://ift.onlinelibrary.wiley.com/doi/full/10.1111/1541-4337.12976
5. https://gcwgandhinagar.com/econtent/document/1586852244Metal%20Packaging.pdf
6. https://foodsafetystandard.in/packaging-requirement-for-food-products/
7. https://www.ppg.com/en-US/packagingcoatings/markets/food-packaging
8. https://packagingcoatings.akzonobel.com/en/food-cans-coatings
9. https://www.webstaurantstore.com/guide/675/types-of-food-cans-and-food-can-sizes-guide.html
10. https://www.sizes.com/home/cans.htm
11. https://www.levapack.com/standard-can-sizes/
12. https://en.wikipedia.org/wiki/Steel_and_tin_cans