1. Nicolas Appert, the French Confectioner Who Invented Canning Without Knowing Why It Worked
Nicolas Appert was a confectioner in France. He was the person who came up with a method of putting food in containers, sealing them, and heating them to make them last, in 1804 [1]. It is said that around the same time, he opened a factory in the town of Massy, near Paris, to make bottled foods [2]. The method was like this: cooked food was put in bottles, loosely corked, and boiled in hot water for 30 to 60 minutes. After that, the corks were pushed in tight to seal them [2].
However, Appert did not have a formal scientific education. He did not understand why this laborious method worked [3]. The reason was unknown, but the method itself was successful. In France at that time, the country had announced in 1795 that it would offer a prize for a food preservation method. The prize was 12,000 francs. Appert received it, and as a condition, he made his method public [3]. In 1810, a book he wrote, "The Art of Preserving All Kinds of Animal and Vegetable Substances for Several Years," was published [4].
Safety Note: The method was released to the world before anyone understood the reason why it worked.
2. How Food Containers Changed from Glass Bottles to Tin Cans Before the Can Opener
Appert’s containers were glass bottles. These bottles changed into metal cans. In 1810, Peter Durand of England patented a method for preserving food in tin cans [4]. After that, Bryan Donkin of the same country built the world’s first canning factory [1]. It is explained that the good thing about cans is that they are less likely to break than glass when handled roughly during transport [5].
However, there was no tool to open those cans. The first patent for a can opener was taken out in 1855 by Robert Yates of England. A more usable one was patented in 1858 by Ezra Warner of the United States. Until then, instructions said to cut open the cans along the rim using a chisel and a hammer [6]. It was about 45 years from the patent for the can to the patent for the can opener. Even so, canned food was used because the contents lasted a long time. So, what was the reason?
3. How Louis Pasteur Showed That Tiny Particles in the Air Cause Food to Rot
Appert is said to have believed that removing air was the reason for preservation [7]. The true reason was understood about 50 years later. In the 1860s, Louis Pasteur of France showed with experiments using swan-neck flasks that spoiling liquids was not caused by air itself, but by particles (microbes) in the air [8].
With this, we can explain why canned food lasts. Canned food is made by putting food in a can, removing the air, sealing it, heating it to kill germs, and then cooling it. Sealing prevents air, water, and bacteria from entering the can. Heating kills the microbes inside [9]. First, you kill the microbes inside, and then you stop them from getting in from the outside. These two things make the food last. To give an analogy, it is like killing the mosquitoes in a room first, and then closing the windows and doors tightly. However, in reality, invisible microbes are killed by heat. The Japan Canners Association (JCA) explains that no sterilizing agents or preservatives are used in canned food [10].
The "removing air" step that Appert valued remains today as a process called deaeration. The purposes listed are to prevent the can from deforming when the air expands during heating, and to prevent corrosion inside the can and changes in color, aroma, taste, and vitamins [9].
Safety Note: The Japan Canners Association (JCA) explains that no sterilizing agents or preservatives are used in canned, bottled, or retort foods. Safety relies on heat sterilization and sealing [10].
4. Why Some Germs Survive at 100°C and How Pressure Heating Solves the Problem
However, heating alone is sometimes not enough. Clostridium botulinum can form very heat-resistant spores. It prefers an environment without oxygen and can cause illness in canned and bottled foods that contain little or no oxygen. Properly sterilized canned food is safe, but if heating is insufficient, the danger increases [11].
Therefore, the manufacturing standards of Japan’s Food Sanitation Act require that for foods where botulinum bacteria grow easily (those with a pH higher than 4.6 and high moisture content), the center temperature must reach 120°C for 4 minutes, or an equivalent heating level [11][12]. It is said that in food heated to this level, all types of botulinum bacteria are dead [12].
The water in a pot does not exceed 100°C, so this temperature cannot be reached directly. A device that heats at high temperatures by applying pressure, like a pressure cooker (pressure retort), was patented by Raymond Chevallier-Appert in 1851. The relationship with botulinum bacteria was understood in the 1920s [7].
On the other hand, it is known that botulinum bacteria do not grow in acidic foods with a pH of 4.6 or lower, even without air. Fruits and tomatoes can be processed with weaker heating [12]. According to the JCA, fruits and jams are treated for a short time at 100°C or less, while vegetables, fish, and meat require pressurized heating at 100°C or more. The conditions differ depending on the food [9].
Safety Note: Properly sterilized canned food is safe, but if heating is insufficient, the danger increases [11].
5. What a 109-Year-Old Steamboat Cargo Shows About Canned Food and the 3-Year Expiration Date
How long does it actually last? It is reported that the National Food Processors Association examined canned food from the cargo of the steamboat Bertrand, which sank in 1865, 109 years later in 1974. The appearance, smell, and vitamins had deteriorated, but there were no signs of microbial growth, and it was judged safe to eat [13]. However, this is a report from a single investigation.
Currently, the shelf life of most canned food is set to 3 years from manufacture. The JCA explains that the expiration date is a date set in advance, before the taste and quality begin to decline. The advance period is called the "safety margin." On top of that, they explain that if unopened and stored properly, it can be eaten almost indefinitely [14]. In other words, 3 years is not a date after which it is dangerous, but a date placed as a guideline for when it is delicious.
However, do not use cans that are bulging. They can bulge due to chemical causes as well as microbes, and not all bulging cans are dangerous, but the JCA advises not to use them as a precaution [10].
Safety Note: Appearance, smell, and vitamins had deteriorated, but no microbial growth was seen, and it was judged safe to eat. The expiration date is set in advance before quality declines, and this advance period is called the "safety margin" [14]. Three years can be read as a date placed as a guideline for deliciousness, not a danger date. Bulging can also be caused by chemical reasons, not just microbes, so it is a precaution [10].
6. How to Read the Expiration Date Printed on Canned Food at Home
If you have canned food at home, look for the date printed on the bottom or lid without opening it. The expiration date is written there. Since most canned food is set to 3 years from manufacture, if a can has a 3-year shelf life, you can estimate when it was made by subtracting about 3 years from the printed date [14]. If you do not have any at home, you can look for dates on cans while they are on the store shelves.
Try guessing one more thing. Which is heated more strongly: canned fruit or canned fish? The reason lies in the story of pH 4.6 in Section 4. The answer is on the JCA’s "How to Make" page, which lists guidelines for sterilization conditions by food type [9]. If you are more interested in the investigation of the Bertrand steamboat cans, try looking up the original article. It may say what kind of cans were tested and how.