Unsafe home canning practices


The composition of a list of unsafe home canning practices will vary depending on who you ask, and how many people you ask.

There will be some major dangers on the list. No doubt, though, a committee could stretch the list to pages long with many additional minor or rare unsafe practices.

This list is just meant to be the high level, major items that reputable home canning authorities would agree upon.

If you are doing any of these, then chances are most safe home canners would say you are doing risky canning.

With those caveats in mind, Healthycanning.com proposes that the greatest unsafe canning practices are, in alpha order:

 1. Aspirin or other pill canning

“No to Canning Pills: ‘Canning pills’ went out with corset-covers. Old manuals might suggest that salicylic acid (read this ‘aspirin’) be dropped in each canning jar before it was capped. Such things never helped then and would not help now. No preservative added can offset dirty handling or inadequate processing.” 1

2. Compost heap canning

“No to Processing in a Compost Heap. Whoever would have thought it? But there was a query based on the notion of holding containers of food at 140 + F/60 + C for a long time.” [Ed: by the heat generated in a compost heap.] 2

3. Crockpot canning

“No to Canning in a Crockpot: We don’t know who could have advocated this, since we have never seen any such claims in print by the makers of Crockpots. But it has come up several times in letters to PFB, usually from writers who say they hope it’s safe, because they felt that slow-cooking was more likely to preserve nutrients than subjecting the food to heats like 240 F/116 C. All we need to say about a Crockpot is that if it’s on a long low-heat setting, chances are that the nastier micro-organisms will be encouraged to grow and breed like mad, and what else should you expect?” 3

4. Dishwasher canning

Trying to “steam process” jars by the heat generated in a dishwasher during a dishwasher cycle.

Processing canned foods during a dishwasher cycle can be dangerous. The temperature of the water during the cleaning and rinsing cycle is far below that required to kill harmful microorganisms. Thus the product will be under-processed and unsafe to eat.”4

5. Microwave-canning

See separate page on microwave canning.

6. Open-kettle canning

Just putting something in a bottle, slapping a lid on it, and if a seal takes hold, considering it done and putting it on the shelf.

See separate page on open-kettle canning.

7. Oven-canning

Taking a short-cut by trying to process bottles in an oven.

See separate page on oven canning.

8. Pressure canning via guesswork

Not following preparation and processing methods and times exactly, including any altitude adjustments required for your location. Following directions that you or someone else have just made up through guess work and reasoning.

9. Recipes — out of date or untested

Using out-dated recipes or untested recipes.

And from Isabel D. Wolf, of the University of Minnesota, about home-canning recipes: ‘avoid following the home-canning advice of celebrities, old cookbooks, ‘back to nature’ publications, and out-of-date home-canning leaflets. Some potentially dangerous instructions can be found in old official publications, even those of this state!’ ” 5

10. Solar-canning

Using the heat of the sun to heat up a box in which you place the jars for procesing.

11. Water-bath canning instead of pressure canning

Water-bath processing low acid food products instead of pressure canning them


Past those points above, though, once you start to expand the list from there, internecine wars start to break out even amongst the “safe canning police” people about venial versus mortal sins.


The greatest home canning danger of all

Out of the above list, the greatest danger of all perhaps is in not pressure canning something that must be pressure canned:

…because in almost every account of an outbreak of food-borne botulism, the Editorial Note deduces that ‘inadequate processing’ or ‘inadequate heating’ allowed the toxin to form, with the help of a bad seal. Spelling it out, this means that low-acid foods that should have been pressure-processed were merely given a Boiling–Water Bath; and that strong-acid foods—which should have been given a Boiling–Water Bath to sterilize container and heat contents adequately—were canned instead by “open-kettle,” or worse.” 6


Further reading

E. M. D’Sa, E. L. Andress, J. A. Harrison and M. A. Harrison. Survey of Home Canning Practices and Safety Issues in the U.S.. Paper 005-04. Presented at the Institute of Food Technologists Annual Meeting, Chicago, IL, July 29, 2007. (Link valid as of March 2015)

University of Nebraska-Lincoln Extension. Unsafe Canning Practices. (Link valid as of March 2015)


Cowboy canners

Cowboy canners

Cowboy canners are the opposite of the Safe Canning Police ; they will stick anything in a jar, close the lid, stick it on a shelf to fester, then feed it to people. They largely purport to trust in the "good old ways" of canning. They take delight...
Fractional sterilization" or "intermittent processing

Fractional sterilization" or "intermittent processing

The early 1900s was a period of much experimentation with different home canning methods. One of the more now hard-to-believe methods devised was called "fractional sterilization" or "intermittent processing." (Outside the canning world, it was often kn...
Home Canning Cured Meats (Bacon, Brined, Corned, Ham, etc)

Home Canning Cured Meats (Bacon, Brined, Corned, Ham, etc)

The past few years there has been a "rasher" of breathless videos and blog posts purporting to impart to people the tightly-held secrets of home canning bacon, hams, pepperoni sausages, etc. The implication is that the reputable authorities in the...
Home-canned cake

Home-canned cake

You cannot safely home can bread or cake. If someone gives you home canned cake, assume it is unsafe to eat and discard it in a manner that not even animals can consume it. See the USDA's procedure for handling suspect food . What is cake in a...
Inversion Canning

Inversion Canning

Inversion "canning" is open kettle canning with one additional step. For the first part, open kettle canning, the food to be bottled is prepared and heated in a pot, then put the jars, after which the lids are applied. No further processing of...
Microwave Canning

Microwave Canning

  What is microwave canning? Microwave canning can be one of two things: attempting to process filled jars by cooking them in a microwave; or attempting to "pressure-process" the jars by placing them inside a plastic microwave pressure...
Open Kettle Canning

Open Kettle Canning

Open kettle canning describes a process whereby food is heated or cooked in an open pot, then put into an open jar, then a lid placed on, and then when the lid seals from the jar or bottle cooling, the jar is put on a shelf. Penn State Extension...
Oven Canning

Oven Canning

Promoted from time to time as a "new" home canning technique, "oven canning" is actually an old technique. It has been around since at least the 1920s -- and it has been discredited and advised against since the 1940s. It involves "baking" your...
Why do you have to process jars of jam?

Why do you have to process jars of jam?

Some people ask why jars of jam must be processed after bottling, in either a hot water bath or a steam canner. They will say their grandmother never did, or they are English and no one English ever does, that they read someone on the Internet...

  1. Hertzberg, Ruth; Greene, Janet; Vaughan, Beatrice (2010-05-25). Putting Food By: Fifth Edition (p. 61-62). Penguin Publishing Group. Kindle Edition.  

  2. Hertzberg, Ruth; Greene, Janet; Vaughan, Beatrice (2010-05-25). Putting Food By: Fifth Edition (p. 62). Penguin Publishing Group. Kindle Edition.   

  3. Hertzberg, Ruth; Greene, Janet; Vaughan, Beatrice (2010-05-25). Putting Food By: Fifth Edition (p. 62). Penguin Publishing Group. Kindle Edition.   

  4.  PennState Extension. Canners and Canning Methods that are Not Recommended. Accessed March 2016.  

  5. Hertzberg, Ruth; Greene, Janet; Vaughan, Beatrice (2010-05-25). Putting Food By: Fifth Edition (p. 45). Penguin Publishing Group. Kindle Edition. 

  6. Hertzberg, Ruth; Greene, Janet; Vaughan, Beatrice (2010-05-25). Putting Food By: Fifth Edition (p. 60). Penguin Publishing Group. Kindle Edition.   

Leave a Reply

Your email address will not be published. Required fields are marked *