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Many home canners would love to can a homemade bread, cake or pie, like zucchini bread, apple pie, banana nut bread, etc. Typically, the breads are baked in canning jars. Then, the canning lids are attached and as the bread or cake cools, a vacuum is formed which sucks the lid fown and seals the jar. The baker/canner figures, "it was hot and the jar sealed, it is sterile and safe!"
Unfortunately it is neither sterile nor safe. Botulism needs 4 things to grow: a food source, a non-acidic environment sucficient moisture and temperatures between 40 F - 130 F. All of these are present in the jar!
And for those who say, "but it's sterile, no botulism in there!". Not
true at all. It takes a lot to kill botulism spores. And since
they are airborne, they're everywhere. As your jar cooled down, it
sucked a little bit of air back in, before it sealed. Air with botulism
spores. In addition to the spores that were already present in the
food that weren't killed during baking. So, the process does not destroy the organism that
causes botulism. And the spores can be introduced into the batter by
being in honey, on grated zucchini, or dust in the mixing bowl, etc.
And, the process of creating a vacuum in jars favors the growth of the botulism microorganism especially in a non-acidic environment. .
Utah State University points out:
A widely distributed recipe for canning zucchini bread has a 45 minute baking time at 325°F. The baking of the bread does not kill the C. botulinum. It is a spore forming organism and spores are resistant to destruction by heat or other environmental factors.
Studies at a number of iuniversities, including at Kansas State University and Utah State University were not able to make a safe canned bread recipe for consumers (See references).
Q: I see canned breads in stores or on the internet! Aren't the proof it is safe to do?
A: These products are made to use very large amounts of sugar and to minimize moisture. Commercial recipes must be lab tested and approved by state or federal food safety authorities and guarantee that it cannot support the growth of the botulism organism. Consumer recipes are not safe and consumers do not have access to the equipment needed to perform tests that would ensure the botulism organism cannot grow.
Commercially produced breads and cakes in jars or cans are available. This product cannot be safely duplicated at home. In making breads and cakes in jars for commercial sale, reputable companies use additives, preservatives and processing controls not available for home recipes. Safety tests are conducted for each specific recipe for commercial products. Avoid purchasing canned breads or cakes in glass jars unless they contain additives to prevent microbial growth and meet all labeling requirements for commercial foods.
Q. Are there any similar but safe alternatives?
An acceptable alternative is to make a dry mix in a jar. Place all of the dry bread ingredients in a jar. Add a commercial oxygen absorber (See here) to prolong shelf life. Attach complete directions to the jar that includes wet ingredients to add (e.g. eggs, oil, etc.) and baking instructions. Be clear that baking should be done in a cake pan or bread pan and not the mason jar."
Q. Can't we modify a bread recipe to make it safe for home canning?
Utah State University says "We have conducted research at Utah State University to see if it was possible to either raise or lower the acid level enough to control C. botulinum or add enough sugar to control water
activity (the amount of moisture available to the microorganism) while still having a palatable zucchini bread. We were unable to formulate a safe product. "
Authorities like Utah State University, the CDC, etc, tell us:
The organism C. botulinum itself is harmless; however, when conditions are right, it can form an extremely potent toxin. Three factors determine if C. botulinum will grow or not:
High concentrations of salt and/or sugar tend to inhibit the growth of the spores.
- a low or nonacid pH,
- adequate moisture and
- an airless or low oxygen environment.
Canned breads meet all the requirements for the growth of Botulinium.
Normally these products are not being held under vacuum and therefore botulism is not a concern.
However, sealing the bread in a jar provides the necessary airless condition. The alternative of putting the lids on after the product has cooled would solve the problem of growth of C.botulinum but the presence of air would allow mold to grow.
One research group looked at the effect of oven
temperatures and cooking times on the safety of banana nut bread with
spores intentionally added to the batter. Half of the samples were
inoculated with a nonpathogenic spore (C. sporogenes) which has a similar
heat resistance to that of C. botulinum. The other half of the samples
were not inoculated. Samples were baked at three different temperatures
(350, 375 and 400 degrees F) from 30 to 55 minutes. Immediately after
baking, the active form of the bacteria could not be detected in either the
inoculated or noninoculated samples. The microbial testing methods were
such that black colonies represented Clostridium organisms, either the C.
sporogenes inoculated into part of the samples or naturally
present C. botulinum or C. perfringens (both are pathogens). Black colonies were not detected in any of the non-inoculated samples immediately after baking; however, they were found at a reduced level in the inoculated samples.
Or in other words, many of the spores survived the baking of the bread. These could become active over time.
A second part of the study was to see what effect storage times would have on the canned bread samples. The banana nut bread baked at 350 degrees F for 30 minutes was considered to be the best quality product, therefore this variable was used for a further storage study. The samples were stored for 90 days at room temperature and at 95 degrees F. Non-inoculated samples held at room temperature did not have detectable Clostridium-like organisms; however, those stored at 95 degrees F did show microbial growth. The higher temperature was more favorable to repair and growth of organisms.
These products would not be
Home made breads, like wheat bread, banana nut bread, zucchini bread, cupcakes, or similar products should be either fresh or frozen.
If some one gives you one "canned" or sealed in a jar, DON'T EAT IT!
Do NOT try to can these; they are almost word for word what the Universities above say you should NOT do!
[ Easy Home Canning Directions] [FAQs - Answers to common questions and problems] [Recommended books about home canning, jam making, drying and preserving!] [Free canning publications to download and print]
Above is the
2020 version of
the Ball Blue Book