First let's get an overview of what botulism is. Botulism is an illness that causes varying degrees of paralysis in the body from a toxin produced by the bacteria Clostridium botulinum. C. botulinum is practically everywhere - just about anything that's touched soil will contain spores. So why don't we get sick from it all the time? Most of the time this bacteria is dormant, and it's only when conditions are right that it grows and makes this toxin. C. botulinum prefers an anaerobic (oxygen-free) environment that's not too acidic, not too salty, not too crowded with other bacteria, and it does especially well at warm temperatures. A unique characteristic of C. botulinum is it's ability to survive high temperatures for relatively long periods of time.
Fermenting foods creates an environment that is antagonistic to botulism. It's what scientists call "competitive exclusion." Beneficial bacteria begin to acidify the food, a condition C. botulinum doesn't like. Adding salt to a ferment also reduces C. botulinum's ability to grow, and encourages beneficial bacteria to take over. There are also other "competitive factors" that beneficial bacteria and fungi create in smaller quantities to exclude pathogenic varieties.
So how often does botulism really occur in fermented foods? According to the CDC reports the leading causes of botulism are (in order of significance):
1) Home-canned foods using improper canning technique (by far #1)
2) Commercially prepared/distributed foods (pasteurized and/or preserved)
3) Improperly stored/handled cooked food (at home and in restaurants)
4) Fermented meats and fish (almost all reports from Alaska)
5) Unkown (very low incidence of undetermined sources)
I did not find a single incident of fermented vegetables, sauerkraut, kimchi, lacto-fermented pickles, kombucha, lacto-sodas, kvass, kefir, yogurt, cheese, etc. The only anomaly was a single case of "fermented" tofu, whereupon reading the detailed report it's clear that the tofu didn't actually ferment - it only marinated in chicken broth, coated in vegetable oil at room temperature for several days after having been cooked.
Fred Breidt, USDA specialist, on fermented vegetables: "There has never been a documented case of foodborne illness from fermented vegetables. Risky is not a word I would use to describe vegetable fermentation."*
So will your sauerkraut give you botulism? NO.
MEATS AND FISH: Practically all the CDC reports of fermented meats and fish were from Alaska, things like buried salmon, beaver tail, seal fat. Fermented meats and fish are a special case. Animal flesh is high in proteins and fats, and very very low in carbohydrates and sugars. The beneficial bacteria need these carbohydrates to thrive. If you plan to ferment meats, it's wise to learn from credible sources. Sandor's book The Art of Fermentation has a whole chapter dedicated to this. If his book doesn't answer any immediate questions, it's well annotated with resources. But meats can be safely fermented.
READ THE FINE PRINT: There's been chatter going around about botulism and carrot juice. Once the dreaded word "botulism" gets linked to some food, people seem to assume there's significant and inherent risk in this food. But nobody bothers to read the fine print. First read the instructions on the upper right, then look carefully at the lower right corner of the label below:
This year (2012) and in 2006 the CDC reported incidents of botulism connected with commercial bottled carrot juice. Products from both incidents were pasteurized. So here's what we've really got: a highly nutritious substrate for microbes, no salt added to encourage salt-loving bacteria or discourage pathogens, low acidity (none added, no fermentation), and it gets heated (pasteurized) just to a point that many (if not most) the good bacteria are killed, but not hot enough to kill C. botulinum.
So carrot juice by itself doesn't give you botulism. Unfermented carrot juice that has been pasteurized, bottled, and sat in a warm truck for an undetermined period of time might.
There's chatter that hot peppers will give you botulism. Chili peppers alone don't give you botulism. Canned peppers using improper canning procedures might.
There's chatter that potatoes will give you botulism. Potatoes alone don't give you botulism. Cooked, unfermented root vegetables incubated in an anaerobic environment (tightly wrapped in tin foil) might.
A FINAL NOTE: Approximately two-thirds of botulism cases reported to the CDC are cases found in infants. These are not considered food-related cases because infants' gut flora has not yet developed to compete with the pathogens we unwittingly ingest everyday. So eat your sauerkraut!
* Quoted from The Art of Fermentation, Sandor Ellix Katz, Chelsea Green Publishing, 2012
Sandor on botulism, video: http://www.youtube.com/watch?v=9QdhSFfaoz0
CDC General Info about Botulism: http://www.cdc.gov/nczved/divisions/dfb ... /botulism/
CDC Annual Botulism Surveillance Reports: http://www.cdc.gov/nationalsurveillance ... lance.html
Detailed case report, Tofu: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5605a2.htm
Detailed case report, Carrot Juice: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm55d106a1.htm
CDC Botulism Manual: http://www.cdc.gov/ncidod/dbmd/diseasei ... tulism.PDF