I’ve been thinking about writing this article for a while, since I’ve explained all of this numerous times over the years, both here and elsewhere; but, when a recent comment on this forum mentioned canning Kale and the response was asking if it could be water bath canned, I knew that folks did not understand some very basic things about canning and botulism. This article will attempt to explain the why of water bath vs. pressure canning; all based on the life cycle of the bacterium Clostridium Botulinum (Cl .Botulinum).
Let’s start with something that everyone probably understands: the common yeast. Yeast is a living organism and like all organisms, it requires food that it digests after which it then excretes waste. In the case of the yeast, the food is sugar and the excrement is alcohol. It’s a simple process that we use to make beer, wine, and distilled spirits.
The bacteria Clostridium Botulinum has a similar life cycle; but, the excrement is one of the most potent and deadly neurotoxins known to exist. To grow, the bacteria requires an anaerobic (low or no oxygen) and a low acid to alkaline (pH greater than 4.6) environment. Since the bacteria covers itself in a spore for protection, it can only be killed by subjecting it to a temperature of 121°C/270°F for 3 minutes.
This leaves us with two options to keep from fatally poisoning ourselves or others.
Kill the Cl .Botulinum, even in its spore form.
This requires the high-temperature pasteurization treatment (121°C/270°F), and since water boils at 100°C / 212°F, a boiling water bath cannot achieve the high temperature required; therefore, pressure canning is required.
Create an environment in which Cl.Botulinum cannot reproduce.
That environment is an acidic environment with a pH of 4.6 or less. This is pretty easy to do when canning most fruits since they have a natural pH that is that low or lower.
Vegetables like corn, beans, and kale, as well as meats, do not naturally have a pH that low, so water bath canning these food items creates a perfect environment for Cl .Botulinum to grow.
This is done by water bath canning fruits with a naturally low pH or by adding acidifiers to the recipe. It’s the reason you may water bath can pickled beets, cabbage, or even meat. While it can be a bit odd to those who haven’t tried it, the German Sauerbraten can be canned this way.
The botulinum toxin itself is inactivated (denatured) rapidly at temperatures greater than 80°C/180°F , so vigorously cooking/boiling may denature/deactivate the toxin in food; but, except in an absolute starvation situation, I would simply discard any suspect food items.
We have probably all heard that we should not give raw honey to infants under 1 year old, and once you understand the life cycle as described above, it becomes obvious. Infants under 1-year-old are generally being fed either mother’s milk or formula and generally have not started eating solid food. The solid food is fed to the child as it develops the Gastrointestinal ability to digest that food, which required stomach acid with a low enough pH to dissolve that food. Prior to this stage of development Cl .Botulinum spores that may be found in raw honey, along with pollen and other things, would find a perfect environment in the GI tract of the young child and would propagate, grow and excrete it’s toxic waste, into that GI tract.
Finally, we have all probably heard of people who talk about water bath canning beans for years with no ill effects, and there are surely people like that who have just been very lucky. Botulism outbreaks still occur with the most recent one I know of being right here in Ohio in April 2015. Here’s the CDC report:
Notes from the Field: Large Outbreak of Botulism Associated with a Church Potluck Meal — Ohio, 2015
Note the table at the bottom of this report that shows numerous outbreaks over the years 1977-2015 all over the country, and perhaps I only knew about this one because it was relatively local here in Ohio.
Here’s an excerpt from that CDC report:
“The attendee who prepared the potato salad with home-canned potatoes reported using a boiling water canner, which does not kill C. botulinum spores, rather than a pressure canner, which does eliminate spores. In addition, the potatoes were not heated after removal from the can, a step that can inactivate botulinum toxin. The combined evidence implicated potato salad prepared with improperly home-canned potatoes, a known vehicle for botulism.”
The underlined word above is my emphasis since this step is not guaranteed to make the food safe.
Following good practices found in places like documentation from your local county extension agency or the Ball Blue Book should always be done; but, for water bath canning of anything questionable, I suggest a kitchen food pH meter that can be purchased from places like Amazon for around $20.00.
So the basic rules are:
Food with a pH less than 4.6 can be safely water bath canned; but, you should still use proven methods for packing and time from the Ball Blue Book or another reliable source.
Food with a pH greater than 4.6 must be pressure canned to kill the Cl.Botulinum, again using the Ball Blue Book or another reliable source
Any questions, ask away because we all want to be safe.
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