Skins and Botulism #360924 - Ask Extension


Skins and Botulism #360924

Asked September 08, 2016, 5:30 PM EDT

Most recipes that are tested safe state to peel things like potatoes and carrots to can, potatoes in particular state its not safe to leave the skins on due to possible botulism. Is it honestly considered safe to make broth from scraps, including carrot, potato, and other root vegetable peels and then can that? Its still putting the same microbes in the broth as canning potatoes but we're straining the solids so I'm trying to understand where the difference is here?

Washington County Oregon

Expert Response

I am assuming you are asking about canning vegetables and broths rather than cooking them to consume right away.  Instructions for canning chunks or whole,  vegetables, call for the removal of skins and peels to ensure there is efficient heat transfer through the product.  Peels and skins are very effective in preventing heat from penetrating the food and can result in cold spots that would allow pathogens to survive. Their presence does add some bacteria load, but appropriate pressure canning should destroy all bacteria, including clostridium botulinum. 
When making broth using the peels/skims for flavor and then straining the solids out, creates a very thin liquid that boils easily and allows heat to penetrate fully, destroying any remaining bacteria. 
Botulism only occurs in the absence of oxygen, such as in a sealed jar.  If the product is being cooked and then consumed, rather than canned, that particular pathogen is not a concern.  Any products that are low acid, which includes vegetables, should be pressure canned, which reaches far above a boiling temperature. That is so the botulism spores are destroyed and cannot grow while in storage in the sealed jar.  
I hope this is clear and helpful.  If you would like to talk about this, remember our Toll-free Food Safety and Preservation Hotline is open Monday - Friday, 9 am - 4 pm at 1-800-354-7319
Jeanne Brandt Replied September 09, 2016, 6:36 PM EDT
I was sharing this with someone and they came back telling me the North Carolina Cooperative Extension has online

"Potatoes must be peeled before canning. Potato skins contain a high bacteria count increasing the chance of Botulium toxon formation." The concern is also those little nooks and crannies might protect any botulism spores that might be present from the heat of processing.

Where is the line here?  Is it heat penetration or the crannies in the food? Is it because the crannies create areas heat can't penetrate. 

The Question Asker Replied October 17, 2016, 11:56 AM EDT
They have a very good point, we want to keep the count of pathogens down as much as possible so that the processing is sure to destroy them.
The crannies would indeed create pockets that would be difficult to heat, sheltering the spores from adequate heat penetration and destruction. 
 I understood you were straining out all the solids before cooking then canning the broth, so the potato skins with their nooks and crannies would not be present to protect the spores during heating.  Scrubbing potatoes well and removing eyes or toughened spots before using the skins in a broth would help reduce the pathogen load.  
Hope this helps clarify more.  If not,  call, or email back. 
Jeanne Brandt Replied October 17, 2016, 1:10 PM EDT
You understood my first question correctly, I'm trying to understand where the lines are.  I'm now contemplating canning potatoes for the winter and I'm not a perfect peeler. I'm being told by naysayers that I must get every last bit of skin off the potato for it to be safe yet other evidence says the issue is heat penetration to the food not the presence or lack of skin on it. If I literally have to scrub them to perfect clean then I'm best to consider another option
The Question Asker Replied October 17, 2016, 1:28 PM EDT
A clear line of what is safe in terms of peels and soil is difficult  to identify.  I am certain that in lab tests, they were very precise in removing every bit of skin and soil before they tested to determine heat penetration during processing, so we don't have a good indication of what the results are when someone is not a perfect peeler.  
Here is a good explanation of storing fresh potatoes, as an alternative to canning them. Potatoes can be blanched and frozen, but try a few first to make certain you like the outcome before freezing too many.  
Jeanne Brandt Replied October 17, 2016, 1:44 PM EDT

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