Appert invented canning in glass containers in 1809. Britain, Napoleon’s chief political adversary, rapidly responded. In 1810 the Englishman Peter Durand received a patent for food preservation. He used containers made of tin-coated sheets of iron hoping to produce a less breakable and more easily transported product. Durand was thus the inventor of the tin can, so called-although tin was only a coating intended to protect the underlying metal from the acids in foods. Canning expanded rapidly.

Can making commenced in the United States in 1812, brought from Europe by Thomas Kensett, an immigrant from England. The Civil War greatly accelerated use of canned foods. Just before the war began in 1861 production was around 5 million cans per year; after the war production had reached 30 million cans. In 1900, less than one hundred years after the basic technology had been invented, the so-called sanitary can made its debut. This was a can made with double-folded seams, the seams covering up the solder and thus preventing its migration into the food. By the early 1920s automated can making had been developed and cans were churned out at the rate of 250 cans per minute as compared to roughly 10 cans per day per laborer before. After that, technological improvements came in stages. Cans began to emerge in the beverage market in the 1950s and aluminum cans appeared in the 1960s. Lead solder gave way to other ways of seaming cans.

Ever more sophisticated coatings were introduced to protect the can from the food and the food from the can. Dual-metal (steel-aluminum) closures were introduced for easy-to-open cans. Cans became lighter, their production more automated, and can making and canning operations more tightly integrated. The purpose of canning is food preservation. From this perspective canning-whether the container is metal or glass-provides the same protection. Both types of containers are vacuum-sealed when holding perishable foods, accomplished by applying seals as the contents are submerged in boiling water. The phrase home canning refers to preserving fruits and vegetables in glass containers. Over time, however, canned food has come to mean food packaged in metal cans. The Census Bureau’s reporting follows this convention. Until 1997 foods and beverages were a single industry category (“Food and Kindred Products”) under the Standard Industrial Classification (SIC) system. After that date, with the introduction of the North American Industry Classification System (NAICS), Food Manufacturing was separated from Beverage & Tobacco Products. In this essay we follow the earlier convention and will discuss both canned food and beverage products under the general term Canned Foods.

Food preservation continues to be the principal reason for using metal cans as packaging. Canning, however, has expanded beyond its original purpose so that some foods are packaged in metal cans even when other packaging would do as well. An example is distribution of cookies, salted nuts, and roasted coffee in attractive metal cans. The great majority of foods and beverages delivered in cans, however, are in metal containers in order to protect them.

Although canned foods as a category is in common use both in popular and in commercial speech, no precise measurement of the total category is available from the Census Bureau. Put more precisely, the Bureau provides census data on a range of major industry subcategories in which the packaging mode is specified. Examples are some of the biggest categories like fruits and vegetables, soft drinks and beer, pet food, dairy products, and salted nuts. In other food categories, however, the mode of packaging is not provided and requires estimates based on such data as, for instance, the industry’s consumption of different kinds of packaging materials. An alternative source of information is provided by the U.S. Department of Agriculture (USDA) which, in reporting on food consumption by the public, identifies quantities consumed in fresh or canned forms.

Data from the USDA dealing with food availability per person per year provide one view of canned food. Thus in 2005 just under 1,650 pounds of food were available for consumption per person, up from 1,634 pounds in 1995. Availability should not be confused with actual consumption because substantial quantities of food are lost in processing. These data also exclude beverages. Of this total, however, around 8.6 percent reached consumers in canned packaging in 2005, down slightly from the 1995 level of 8.7 percent. In that these data inevitably miss some of the food that ends up in cans-because no basis is provided for a good estimate-it may be reasonable to assume that approximately 10 to 12 percent of all food may come to us in cans of some sort. Major categories include:

• Fruits: 17% of all food, 6.1% canned
• Vegetables: 25% of all food, 25.3% canned
• Dairy: 17% of all food, 0.6% canned
• Meat and Poultry: 11% of all food, 2.5% canned
• Fish: 1% of all food, 15% canned
• Fats and Oils: 5% of all food, 12% canned
• Tree Nuts: 0.2% of all good, 15% canned
• Coffee: 0.6% of all food, 53% canned
• All Other: 23% of all food, the canned proportion unknown The All Other category includes grains, dried legumes, sweeteners, eggs, and peanuts. It is possible to produce a rank order of canned foods from this listing by weighting the canned portion by the quantitative magnitude of the food category. Using that method, the top five categories of canned foods are vegetables, fruit, fats and oils (primarily vegetable shortenings), coffee, and fish (primarily seafood). Another way of looking at the category is from an industrial perspective. A look from that viewpoint will be carried out under the Market subheading below in which, alongside the look at food, beverage packaging in cans will be included as well.

The Canning Process

The principal object of all food preservation is to prevent bacterial activity in the food from causing it to spoil. The major approaches to this end have been drying, pickling, salting, smoking, and freezing. Bacterial activity requires water which, removed in drying, inhibits bacterial action. Pickling preserves food by creating an acidic environment intolerable to most microorganisms. Cheeses, for instance, are stabilized by the presence of lactic acids produced by certain bacteria feeding on milk-sugar, making it difficult for other pathogens to live. Salting causes cell dehydration and kills off bacteria; salting is a type of pickling. Smoking causes antioxidants to be present in food and these suffocate bacterial life. Freezing immobilizes the water that bacteria need to live. The innovation introduced by canning depended on two factors. One was hermetically sealing of containers and the other was heat sterilization. Bacterial organisms are killed off by the application of high heat applied to a sealed container. The seal is tight enough that bacteria cannot reach the food again until the can is opened. Using fruit and vegetable canning as examples, the process of canning itself may be envisioned as four major operations, the two central steps are unique to the canning process itself.

Food Preparation and Filling

Fruit canning begins with washing the fruit, a sorting and grading step, peeling and coring of products that require it, chopping and slicing if desired, and optionally cooking of the fruit before it is placed in a can. Vegetable processing is similar but with some of the steps arranged in a different order. Most vegetables are subjected to blanching after being washed, sorted, and cut. Blanching is intended to kill off bacteria by immersing the vegetable briefly in boiling water. Vegetables are peeled, if required, after blanching and/or cooking. Another wash cycle follows peeling.

Container Sealing

Filled containers are vacuum sealed. This means that air is drawn out of the container immediately before it is sealed, accomplished either by sealing the cans while their contents are hot or sealing them in a vacuum chamber. The object is to create a pressure inside the can lower than atmospheric pressure to keep seals tight, to remove as much free oxygen from the can as possible, and to keep cans from bulging later if used at high altitudes. When hot water vapor condenses into steam in a closed chamber, a vacuum is created. If some of the air is also evacuated from the chamber, vapor condensation is even more effective. Steam tunnels or locally applied steam condensation is used in creating a vacuum during can sealing.

Heat Sterilization

This crucial process in canning follows sealing. It is produced by heating the containers briefly to a boiling temperature. In many modern processes, sterilization of the product and of the container itself are separated. At the point of filling, a sterile product is placed in a pre-sterilized container.

Cooling, labeling, and storage. The hot product is next cooled and dried. After that labels are affixed, cans are placed in packing boxes, and the boxes aggregated onto pallets for transport to the warehouse. Variations on this general scheme characterize all canning operations. Differences arise from the kind of product canned, its levels of natural acidity, and whether or not the process is continuous or handled in batches.