Source
r/askscience•
Proeliata

Botulism, how does it work?

My friend and I had a conversation the other day that surfaced a longstanding confusion of mine. We had roasted some potatoes wrapped in aluminum foil in a campfire, and a few were left over. The next day as we were packing up, she said that we probably shouldn't eat those as she had heard that someone died of botulism poisoning after eating a baked potato. I said that sounded a bit like an urban myth, but some Googling unearthed that this does seem to have happened at least once. My questions are mostly about the "anaerobic environment" part of the required conditions:

  1. I had always understood this to mean that the food item needs to be cut off from the air completely. Will foil-wrapping really achieve this? Do other people foil wrap their potatoes that well?

The answer to this, apparently, is that trace amounts of oxygen are tolerated by C. botulinum. Thanks, thiskittensgotclaws!

  1. As my friend mentions, would the inside of the potato be in an anaerobic environment since it's obviously not in contact with the air even if the potato isn't foil wrapped? Why aren't all potatoes dangerous then? Would a boiled potato be likely to harbor botulism?

  2. I've heard of the dangers of botulism in sous vide chicken--is that because it's cooked vacuum sealed? But chicken isn't grown in the earth, so I'm not sure I understand how this works.

Finally, I had heard the advice that raw garlic should not be stored in olive oil, but never heard that about cooked garlic. If cooked garlic is fine, then why aren't the potatoes?

Posted Jul 17, 2012, 1:07 AM UTC · edited

18
thiskittensgotclaws•

Checked wiki to confirm that C. botulinum is in fact an obligate anaerobe and it says that C. botulinum "tolerates traces of oxygen due to the enzyme superoxide dismutase (SOD)." So that could explain why just foil wrap is sufficient for growth.

2
pete_and_repeat•

anerobic environments created artificially (through packaging i.e. aluminum foil, vacuum packaging) or naturally (like the inside of your baked potato) would facilitate the growth of Clostridium botulinum, granted the spores were present in the first place. These spores can be avoided by good farming principles and asceptic handling during food processing. The soil where your potato is grown is also a great anaerobic environment. So yes, your potato could have at one point harbored C. botulinum spores/toxin.

However, there exists a value called the D-value, which is the amount of time at a specific temperature necessary to cause a one log reduction in the number of microbes present. For C. botulinum at 121C, this is 0.2min. So I imagine your campfire is hotter than this, and you roasted them for idk...half an hr? Should be plenty sufficient of a time-temperature combination in order to kill the microbes (same thing with cooked garlic) (you can look up charts of these time/temperature combinations). Also, there's a certain concentration of toxin that needs to be present in order to illicit a toxic response. An adult can ingest some amount of botulinum toxin and be ok due to the microflora in the gut that can metabolize it. However, this is not true for infants who don't have these microflora. That's why you shouldn't give honey (anaerobic environment) to infants.

2
ProeliataOP•

Why the prescription to avoid foil-wrapped baked potatoes vs. unwrapped baked potatoes then, if the inside of the potato is also a great anaerobic environment? Wouldn't all potatoes be equally dangerous to eat then?

1
pete_and_repeat•

Sorry about that... I should've included this relevant info in my original post: C. botulinum can only get to the inside of the potato if there are cuts or bruises on the surface of the potato (sorta like C. tetani and it getting into the human body). so...what I imagine your source is getting at is if you did wrap your potato in aluminum foil and you failed to reach a sufficient time-temperature combination to kill C. botulinum, your spores would live on due to the favorable environment. but if you had an unwrapped baked potato and were exposing the skin of the potato directly to your heat source + the combination of an aerobic environment...you'd kill your spores/toxin.

1
GrandmaGos•

Botulism and the foil-wrapped baked potato. Not an urban myth.

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ProeliataOP•

Yeah, like I mentioned in my post, I already realize that it's not a myth.

1
GrandmaGos•

The link explains how it works and answers the first two of your questions.

1
ProeliataOP•

Not really. I still don't understand how foil wrapping a potato can cut it off from oxygen that well. It doesn't address the question about whether the inside of a potato is an anaerobic environment at all.

1