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I am looking for the criteria that make an acceptable recipe for canning. Most sites say to only use approved canning recipes and not make substitutions, which is totally understandable, but surely there must be some guidelines for what makes those recipes acceptable? What levels of salt, acidity, water activity, etc make a recipe suitable to be canned?

Michael Liebman
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SourDoh
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1 Answers1

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Nearly any recipe can be canned, the only caveats are that lower-acidity foods and recipes require a specialized pressure canner to kill bacteria, and there is also a short list of ingredients which are never a good idea to can, but many people wouldn't think twice about adding/subbing into a recipe - fats, dairy and eggs shouldn't be in a canning recipe because they'll still go rancid, grains and flours are good insulators and will actually protect bacteria from the heat, and thickeners that people will often throw into a recipe like cornstarch or tapioca will chemically break down from the canning heat. You'll find plenty of cases of people canning grainy/floury things anyway with no ill effect, but that simply means there was no bacteria to kill in the first place. Better safe than sorry.

Most people don't even know what pH is, let alone how to test it or how a recipe alteration would change it. They also aren't going to know much about bacterial growth conditions or heat transfer. It's a heck of a lot easier for a recipe site or book to just say "no substitutions" than to try to teach people how to do it safely, especially when there's plenty of idiots who wouldn't pay attention and sue when they get bacterial poisoning.

So there's really only two guidelines you really have to worry about for your recipes:

  1. Avoid the ingredients that shouldn't be canned, or at the very least, understand that you're taking a risk.
  2. Foods with a pH level of 4.6 and below can be canned in boiling water. A pH of above 4.6 requires pressure canning. This pH chart gives some examples of commonly canned items.

Sources:

  • The acidity rule is a fundamental safety rule that any decent guide will have. Ball's guide mentions it first thing in "Getting Started". Most guides will simply refer to high-acid and low-acid foods. This safety guide from the National Center for Home Food Preservation details the pH reading of 4.6 as the dividing line, which is also visible in the pH chart linked in the answer.
  • The dangers of canning cakes and breads have been published by many research departments, including those at Penn State and University of Georgia
  • Thickeners such as cornstarch chemically breaking down due to the heat involved in canning is detailed in the Cook's Thesaurus. This breakdown is the entire reason for a product called Clearjel, which is also mentioned on the same page as a substitute for cornstarch
  • Clemson University states that no safe methods for home canning dairy products exist.
Barkode
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  • Do you have sources for any of this? – Cascabel Apr 28 '16 at 18:58
  • There's also the problem of 'dense foods', in which you have to also worry about how thickly you cut the food so that the acids can properly penetrate them. (pumpkin pickles are when I typically see this mentioned) – Joe Apr 28 '16 at 19:38
  • @Jefromi I added some concurring academic sources to the answer. – Barkode Apr 28 '16 at 20:12
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    Building on what Joe mentioned, pH can change after canning as the acid comes to equilibrium with the food. So home canning recipes based on a pH you measure yourself at canning time can be wildly unsafe. I *think* your second guideline is correct, it's just that in practice it's actually pretty hard to follow. – Cascabel Apr 28 '16 at 20:14
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    Some other odds and ends: how do you know what shouldn't be canned? Does it include anything besides grains/starch? And even if you know, say, that boiling water canning is safe for a given food, how do you know what processing time you need for safety? – Cascabel Apr 28 '16 at 20:16
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    The acid level in pickles (which Joe mentioned) is too low to get anywhere near 4.6. If the pH in something else is too close to call, common sense would dictate to err on the side of caution and use the pressure method. Measuring the level yourself is perfectly fine and how to do so detailed in most canning guides. How else do you think it's determined if not by measuring? I also cited the largest (and 125 year old) manufacturer of home canning supplies as well as the largest national association for it; if they aren't authoritative enough please suggest who would be. – Barkode Apr 28 '16 at 21:57
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    Additionally, yes the list of things that shouldn't be canned contains more than grains and starch. I detailed as much in my answer, and cited publications from the science departments of major research universities. As far as the processing time goes, there are tables based on altitude and jar size in every canning guide. It isn't some mysterious arcane knowledge, anyone who cans at home uses those tables unless it's an item they've done so many times they just remember from experience. This is complete common knowledge for anyone who has ever canned anything or even read a beginner guide – Barkode Apr 28 '16 at 22:08
  • Clarity: "the danger of canning bread in *glass jars*". Let's not put B&M Brown Bread out of business. – Paulb Apr 29 '16 at 18:25
  • @Barkode I'm suggesting things that should be clearly addressed in your answer, not saying they're all impossible to know. Remember, you're answering a question from someone who *doesn't* know all this stuff, and other beginners will read it too. You really don't want any of them to get a dangerously oversimplified impression from your answer. – Cascabel May 04 '16 at 05:24
  • Also, I've seen totally different processing times for different fruits/jams, even for the same jar size and altitude. So it sure seems like you can't actually know what time you need without finding an already existing recipe for the specific thing you want to can. – Cascabel May 04 '16 at 05:28
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    The question specifically asked what makes a recipe suitable for canning. Home canning is nothing more than killing existing bacteria and inhibiting future growth. The entire answer to this question is to simply avoid anything which can rot after being canned or will prevent the heat from killing the bacteria. That isn't an oversimplification. Creating any recipe, canning or otherwise, requires a modicum of common sense. Those who lack it should stick to the recipe no matter what they're doing. – Barkode May 04 '16 at 16:01
  • I think cases have been found where light bacterial activity actually messed with the pH, resulting in other bacterial activity... – rackandboneman Aug 29 '16 at 09:07