What is the definition of home canning?

While people associate the word “canning” with “cans”, as in “tin cans”, it actually comes from the word “canister” (from which the word “can” is also derived.) Canning refers to a defined heat process of preserving food in canisters of various materials.

Definition of the word “canning”

Encyclopaedia Britannica says,

Canning, method of preserving food from spoilage by storing it in containers that are hermetically sealed and then sterilized by heat. The process was invented after prolonged research by Nicolas Appert of France in 1809… Appert’s method consisted of tightly sealing food inside a bottle or jar, heating it to a certain temperature, and maintaining the heat for a certain period, after which the container was kept sealed until use… In 1810 Peter Durand of England patented the use of tin-coated iron cans instead of bottles…. In the late 19th century, Samuel C. Prescott and William Underwood of the United States set canning on a scientific basis by describing specific time-temperature heating requirements for sterilizing canned foods.” ^[1]”Canning”. Encyclopædia Britannica. Encyclopædia Britannica Online. Encyclopædia Britannica Inc., 2015. Web. 14 Dec. 2015. <https://www.britannica.com/topic/canning-food-processing>.

The Hazel-Atlas jar company gave this definition

Canning is a method of using heat and air-tight containers to preserve food as nearly as possible in the condition in which it would be served when freshly cooked.” ^[2]Canning Helps By Hazel-Atlas. Page 2. C. 1940s. The Alan and Shirley Brocker Sliker Collection, MSS 314, Special Collections, Michigan State University Libraries. Available at https://www.lib.msu.edu/exhibits/sliker/detail.jsp?id=6195.

To be clear, canning refers to a heat treatment process, not to the type of container that a food item happens to be canned in.

In the photo immediately below, the Kraft Miracle Whip, and the Marks and Spencer’s pickled beet (beetroot), have both been canned in plastic bottles. The Tiptree jam has been canned in a single-use glass jar, the relish in an infinitely re-usable Mason jar, and, the bamboo shoots in a single-use metal tin.

The origins of the word “canning”

The canning process was first called “Appertization”, named after Nicholas Appert, who came up with a process at the dawn of the 1800s for preserving food in bottles sealed with a cork, then boiled.

The modern term “canning” comes from the word “can”, which is short for “canister.” Canisters can be made of metal or glass (or even plastic or cardboard these days.)

When you “can” something, you are putting it in a canister, sealing it in that canister, and processing that canister to make the food in it shelf-stable and safe for later consumption even in the absence of refrigeration or freezing.

The term refers to the process of “canistering” something, rather than the actual material of the canister used.

Canning can happen commercially, and at home.

Commercial canning uses both jars and metal tins. Home canning used to use metal tins, and canning guides routinely included directions for using tin cans, but jars won out because they were re-usable, and, especially during World War Two, didn’t require the amounts of metal that were needed for the war effort.

The National Center for Home Food Preservation (NCHFP) says,

Canning is a method of food preservation where food is placed in a jar or can and is heated to a temperature that destroys microorganisms in the food. The heat also inactivates enzymes in the food that can cause spoilage. As a jar is heated, air is driven from the product and the jar. When the jar cools, a vacuum seal is formed. The vacuum seal holds the lid on the jar, prevents the food from drying out and prevents recontamination of the food. The canning process in glass jars is different from canning in metal cans. Air is not driven from cans after they are sealed as with glass jars. Products are heated in order to kill microorganisms. The product is said to be “commercially sterile” when all disease causing organisms have been killed. The organisms that survive can cause the food to spoil if it is stored at temperatures above 95°F (35 C). These may produce gases or cause bad odors. However, they will not cause illness.”  ^[3] National Center for Home Food Preservation Self Study Course. Module 2. General Canning:  How Canning Preserves Food. Accessed March 2015.

How do the experts define home canning?

Bernardin says,

Home canning is just one step beyond cooking… Proper, safe home canning procedures interrupt normal food spoilage and decay.”  ^[4] Bernardin Guide to Home Preserving. Toronto, Canada: Bernardin Ltd. 2013, page 4

Public Health Ontario (Canada) points out that the term “home canning” is now also used for small, artisanal commercial canners:

Canning is the method of food preservation where food is treated by the application of heat alone, or in combination with pH and water activity, then stored in hermetically sealed containers. Home canning is the process of preserving foods such as fruits, vegetables, and meats, by packing them into glass jars and heating the jars to eliminate organisms that would create spoilage… Traditionally, home canning was a term used for canning at home; however, it is now also commonly used for small scale canning operations who sell to the public at food establishments and farmers’ markets. There are two different processing methods for home canning: boiling water bath canning and pressure canning. Boiling water bath canning is used for high-acid or acidified foods, while pressure canning is applied to low-acid foods.”  ^[5]Parto, Naghmeh. Ontario Agency for Health Protection and Promotion (Public Health Ontario). Home canning: literature review. Toronto, ON: Queen’s Printer for Ontario; 2014. ISBN 978-1-4606-4166-8 [PDF] page 9.

Can you reproduce at home all commercially-canned products?

You are just not going to be able to replicate everything you see at the store in jars and cans. There is just not the technology yet available to safely and consistently can the wide extent of foods that industrial packers are able to.

The National Center for Home Food Preservation says, “It is not always possible to home can foods like those that are commercially available/store-bought, or your own recipes.  ^[6] Canning your own salsa recipe. National Center for Home Food Preservation. July 2008. Accessed January 2015.

But home canners may console themselves with this knowledge: the products that they are able to can at home will be of much higher quality than commercial.

How does canning work?

A journalist named Jonathan Ewald seems to have done a decent job of summing up how canning works:

The canning process is quite simple. First, a tin can or glass jar is filled with food and liquid (usually water). After the container has been sealed, it is heated and often put under pressure. This process kills any microorganisms that could cause illness or spoil food. When the can or jar is removed from the water, the air inside compresses and seals the contents off from the outside world. The seal then protects the food from new microorganisms entering and from oxidization from the air. After this, the food can be conveniently stored and enjoyed at a later date.”  ^[7] Ewald, Jonathan. What is canning and what are the benefits? 7 August 2014. Accessed March 2015.

Putting Food By says,

For its effectiveness, canning relies on applied heat and the exclusion of air….How much heat depends on the acidity of each particular food we intend to can…”  ^[8] Hertzberg, Ruth; Greene, Janet; Vaughan, Beatrice (2010-05-25). Putting Food By: Fifth Edition (p. 45). Penguin Publishing Group. Kindle Edition.

Elizabeth Andress of the NCHFP says that canning is preservation by heat and vacuum.  ^[9] Andress, Elizabeth. “History, Science and Current Practice in Home Food Preservation.” Webinar. 27 February 2013. [48:00] Accessed January 2015 at https://nchfp.uga.edu/multimedia/video/nchfp.wmv Food is placed in a jar or can, and and then heated to a temperature inside the canister which destroys micro organisms that can cause food poisoning and destroys naturally-occurring enzymes that would cause spoilage. At the same time, the processing drives air from the jar, and thus creating a vacuum seal.

What canning methods are there?

As of 2014, the USDA recognized two methods of canning  ^[10] Andress, Elizabeth. “History, Science and Current Practice in Home Food Preservation.” Webinar. 27 February 2013. [42:00] Accessed January 2015. :

• immersed boiling water bath, and
• pressure canning

In French, the two processes are referred to as « eau et autoclave » : with “eau” meaning “water”, and “autoclave” meaning “pressure canner.” To pressure can in French is: « stériliser à l’autoclave. »

• Boiling water processing is for foods that are acidic (with a pH below 4.6);
• Pressure canning is for foods that are low-acid (with a pH 4.6 and above).

Boiling water bath canning involves:

• Removal of oxygen
• Sealed jar or can (so nothing can re-enter)
• Heat (boiling water temperatures)
• Acidity (natural and / or added that inhibit microorganisms from being able to function)

Pressure Canning involves:

• Removal of oxygen
• Sealed jar or can (so nothing can re-enter)
• Heat (pressure temperatures)

Water bath canning will let you do tomatoes, fruits, jams, jellies and pickles. But that’s it. When you want to move beyond that, you have to bite the bullet and tackle the scary topic of a pressure canner.

As of 2015, a third method is on the brink of being recognized, that of steam canning, as an equivalent, it seems, of water bath canning.

Canning times

These are referred to as processing times: how long you “cook” a jar in the canner.

There are scientifically determined methods and processing times for canning each type of food. You don’t just guess.

In order to establish safe home-canning methods, it is necessary to verify that processes deliver sufficient thermal lethality. Thermal processing operations in the canning industry aim to ensure adequate destruction of expected spoilage organisms and pathogens in the product based on reliable microbial thermal-death-time information. The primary public health concern associated with low-acid canned food is the formation of botulinal toxin in the container (Weddig 2007); with acid or acidified canned foods the threat to public health is from Escherichia coli O157:H7 (Breidt et al. 2010) or Listeria monocytogenes (Breidt et al. 2014).  ^[11] Etzel, M. R., Willmore, P. and Ingham, B. H. (2014), Heat penetration and thermocouple location in home canning. Food Science & Nutrition. doi: 10.1002/fsn3.185 https://onlinelibrary.wiley.com/doi/10.1002/fsn3.185/full

Labs determine the cold spot in a certain sized jar with a certain food in it, then innoculate that jar with nasties, put “thermometers” in the jar and determine how much time and heat is required to kill the nasties off even in the coldest spot of the jar.

Canning versus preserving and pickling

Some food writers distinguish between preserving, pickling and canning.

• Canning: Plain vegetables, meat, savoury foods, whole fruits
• Pickling: Stuff that is pickled with acid, usually vinegar
• Preserving: jams, jellies, relishes, chutneys, compotes, etc.

Note that not all pickled items are canned, they may just be stored in a fridge, or a crock. And not all jams and jellies are canned: they may be fridge jam or freezer jam. (Most people wouldn’t call freezer jam canning.)

But to make either pickles or preserves safe for shelf storage, their jars have to be processed by water bath canning, which makes them also canned goods as far as the world of food science is concerned, because they have now been through the canning process.

Canning is just one aspect / technique of the broader category of food preservation. Food preservation takes in canning, drying, fermenting, freezing, putrefying (sic), salting, etc.

Canning versus bottling

In the UK, Australia and New Zealand, people tend to presume that their term “bottling” is interchangeable with the North American term of “canning.”

It is not.

Canning is a definite science-based process with procedures, guidelines and rules set down by recognized authorities in the field. Bottling is more guesswork, hearsay and experience of others. It may or may not involve processing of the filled jar (often it doesn’t), and if it does, the processing times aren’t based on the kind of lab-based evidence discussed above to ensure quality and safety of the product.

The National Center for Home Food Preservation says,

[Many recipes in circulation on the Internet] are not really canning, as they do not have Boiling Water or Pressure Canning processes applied to the filled jar. True home canning is when the food is heated enough to destroy or sufficiently acid enough to prevent growth of all spores of Clostridium botulinum (that causes botulism) and other pathogens during room temperature storage on the shelf.”  ^[12] National Center for Home Food Preservation. Frequently Asked Canning Questions. Accessed March 2015.

Is canning safe?

There is safe canning, debatable canning, and unsafe canning.

Roxie Dinstel from the University of Alaska says, “Canning is a perfectly safe method of preserving food, if directions are followed.”  ^[13] Dinstel, Roxie Rodgers. Food Preservation. Back to Basics, Lesson 1. University of Alaska Fairbanks Cooperative Extension Service. FNH-00562A. Revised March 2013.

Author Skip Plemmons says, “Canning is a safe, economical way to preserve food, as long as you carefully follow directions to the letter, especially regarding processing temperatures and times.”  ^[14] Plemmons, Skip (2014-09-14). Next Generation Home Canning: Contemporary and Fun Recipes for Beginners . . Kindle Edition.

USDA canning procedures have massive safety margins built in.

The history of canning

The canning process was originally an answer to a military question of how to ensure army food that was easy to transport and non-perishable while at the same time safe to eat, protected from spoilage, pests, infection by foodborne illness, etc.

Some people add to the original purpose of canning: take food that is fresh now, and store it in a safe fashion for future use.

The commercial canning foods for ordinary consumers first took off in London, packaging the food in metal “canisters.” The word soon got shortened to “cans”, and then soon, the process was described as canning.

So even though the name of the process is based on “canisters”, the process term took on a life of its own to describe heating food in sealed containers for safe storage.

When jars came along, they enabled canning to happen in canisters that were reusable, with cheaper equipment.

After 1900, home canning of all types of food, mainly in glass jars, became popular as a means of utilizing home garden products, providing better diets, and reducing the cost of living.

Home canners began being competition to commercial canners. H.J. Heinz, founder of the Heinz company, felt that his biggest competition was not other commercial canners, but home canners:

In fact, while Heinz had the largest share, about 20 percent of the ketchup market, his biggest competitors were homes, making up almost 18 percent of the market. Home canning was driven by the 1868 invention of the ‘Mason’ Jar. The Mason jar had a sealable lid and metal ring. Its use in home canning was limited by the cost of hand-blown jars, which was coming down with automated glass jar and bottle making machines. A glassblower (supported by four to six man crew) could do about 350 jars a day, but the Owens machine made 3,500 jars per machine worker per day. The price of Mason jars plummeted, and home canning was increasing exponentially by 1904. The Ball Brothers in Muncie, Indiana, were making Mason jars available to all. Home canning had significantly hurt sales of Heinz’s traditional line of jellies and fruit preserves. The public concern for manufactured food purity only strengthened the home canning industry. Like many great industrialists of the time, Heinz had a natural sense of the direction of the marketplace. Questions of purity hurt all food processors both home and abroad, but again Heinz took the offensive and moved to the forefront in advancing food purity.”  ^[15] Quentin R Skrabec. H. J. Heinz: A Biography (p. 153). Kindle Edition.

Home canning did indeed involve cans

Home canning used to involve tins, and it still could, if you really wanted to. The USDA says,

Food may be canned in glass jars or metal containers. Metal containers can be used only once. They require special sealing equipment and are much more costly than jars.”  ^[16] United States Department of Agriculture (USDA). 2015. Complete guide to home canning. Agriculture information bulletin No. 539. Page 1-8

While the USDA has stopped giving explicit directions for using tin cans as an alternative to jars, some university extensions such as the University of Alaska Extension still do (as of 2015.)

Up until the 1940s, booklets still included instructions on how to actually can in cans

By the 1930s, home canners certainly preferred glass jars over tins. A researcher at the time at the University of Massachusetts wrote,

Commercial preservation of food materials is done almost entirely in tin containers because of the ease of handling in rapid production methods and the reduction of the breakage factor to a minimum. Home preservers and small scale producers of preserved foods do not have the factor of speed and breakage to contend with and in using glass have the advantages of the reuse value and the appearance of the product itself.” ^[17]Maclinn, Walter Arnold. Some internal physical conditions in glass containers of food during thermal treatment. Master thesis. University of Massachusetts. 1935.

Note the researcher mentions an advantage of glass jars that would certainly still be true today: filled glass jars are ‘prettier’, and allow you to show off your work better, than a boring old tin can.

The definitive swing to home canning being almost entirely done in glass jars happened during World War Two. Government home economists advised at the start of the war,

Glass jars are more economical for home canning than tin cans, as they can be used over and over again and the cost be spread over several years.”  ^[18] McKimmon, Jane S. and Cornelia C. Morris. Simplified Methods for Home and Community Canning. North Carolina Agricultural Extension Service. Pamphlet #39. March 1941. Page 3.

The two world wars brought about the first two big booms in home canning

The US government began encouraging home canning during World War One:

Before 1920, canned foods were primarily reserved for military usage. In fact it was during World War I that the US government encouraged its citizens to start canning food in their homes so that more supplies would be made available for their armed forces overseas.”  ^[19] Heller, Max (2014-10-29). Canning and Preserving: Learn How to Can and Preserve Vegetables, Fruits, Meats and Jams for Beginners (Kindle Locations 67-69). . Kindle Edition.

World War Two turned home canning from something that poorer people did, into a patriotic activity for the middle classes:

In 1943, 20 million households raised Victory Gardens, and all those vegetables weren’t eaten fresh.  Steel was directed to pressure-cooker production instead of munitions, and a massive effort was made to educate people in the skill of canning.  ‘Department stores ran films and displays on canning, society ladies enrolled in classes on it, home economists lectured on it to ladies’ clubs, extension agents demonstrated it to farmers’ wives, and charities taught it in the slums,’ wrote food historian Harvey Levenstein in ‘Paradox of Plenty.’  ^[20] Halloran, Amy. Preserving the Art of Canning Safely at Home. Seattle, Washington: Food Safety News. 26 April 2011. Accessed March 2015. 

The majority of today’s recommendations for processing are still based on research done during the Second World War.”  ^[21] Andress, Elizabeth. “History, Science and Current Practice in Home Food Preservation.” Webinar. 27 February 2013. Accessed January 2015.

Further reading

Penn State Extension. Selecting a Canning or Processing Method.   23 June 2012.

Riggs, Kathleen. Avoiding Common (Major and Minor) Canning Mistakes. Utah State Cooperative Extension. March 2009. FN/Food Preservation/2009-01.