Fermentation Food Safety
Like any food, there are certain health risks associated with fermented foods. These risks are vastly overstated in the media.
Foodborne botulism has often been from home-canned foods with low acid content, such as asparagus, green beans, beets and corn and is caused by failure to follow proper canning methods. However, seemingly unlikely or unusual sources are found every decade, with the common problem of improper handling during manufacture, at retail, or by consumers; some examples are chopped garlic in oil, canned cheese sauce, chile peppers, tomatoes, carrot juice, and baked potatoes wrapped in foil. In Alaska, foodborne botulism is caused by fermented fish and other aquatic game foods. Persons who do home canning should follow strict hygienic procedures to reduce contamination of foods, and carefully follow instructions on safe home canning including the use of pressure canners/cookers as recommended through county extension services or from the US Department of Agriculture. Oils infused with garlic or herbs should be refrigerated. Potatoes which have been baked while wrapped in aluminum foil should be kept hot until served or refrigerated. Because the botulinum toxin is destroyed by high temperatures, persons who eat home-canned foods should consider boiling the food for 10 minutes before eating it to ensure safety.
See especially [Preparing and Canning Fermented Foods and Pickled Vegetables http://nchfp.uga.edu/publications/usda/GUIDE%206%20Home%20Can.pdf]
Information on fermented foods is limited to sauerkraut and traditional dill pickles.
Most online sources for information on kombucha culture are of extremely poor quality. Many enthusiast blogs, sites, and message boards warn that the entire culture should be thrown out immediately if any mold is detected on the Acetobacter pellicle, but they do not cite any references as to why. To make matters worse, most of these sites are also looking to sell you supplies to replace what they tell you to throw out.
In the production of sauerkraut, kimchi, and related fermentations, mold is a relatively common occurrence - in these processes, it is universally accepted that it is perfectly safe to skim off the mold and continue with business as usual. While there are fungi that pathogenize humans, the probability of finding one of these organisms growing on your food seems vanishingly slim. If there is a danger to mold in food, it will more likely be related to the presence of mycotoxins (Aflatoxin in peanuts immediately comes to mind) produced by the fungi, instead of the presence of the fungi themselves.
Aspergillus niger is one possible food contaminant: http://en.wikipedia.org/wiki/Aspergillus_niger There is evidence that some strains may be capable of producing mycotoxins such as ochratoxin. Ochratoxin A, in particular, is a suspected carcinogen that can cause neurological damage and renal failure:
"Those foods contain N-nitroso compounds, which are likely carcinogens"
"When Chinese hospitals started systematically tracking cancer incidence 50 years ago, they found that certain regions suffered from startlingly high rates of esophageal squamous cell carcinoma, a cancer of the cells lining the esophagus. Epidemiologists observed that people in these areas relied on fermented vegetables for nutrients for long parts of the year, when fresh veggies weren't available."
"Our results suggest a potential two-fold increased risk of oesophageal cancer associated with the intake of pickled vegetables. However, because the majority of data was from retrospective studies and there was a high heterogeneity in the results, further well-designed prospective studies are warranted."
"Endogenous N-Nitroso Compounds (ENOC) and Gastric Cancer in EPIC-EURGAST Study"
"Nitroso compound (ENNG) synergistically affects H pylori-induced gastric cancer in non-human primates"
"We observed that a high intake of fresh vegetables was significantly associated with a decreased risk of GC (overall summary OR = 0.62, 95% CI = 0.46-0.85) but that a high intake of pickled vegetables was significantly associated with an increased risk of GC (overall summary OR = 1.28, 95% CI = 1.06-1.53)."
"Among the papers not to be found in the vast library of the kimchi museum is one published in June 2005 in the Beijing-based World Journal of Gastroenterology titled "Kimchi and Soybean Pastes Are Risk Factors of Gastric Cancer.""
"Other studies have suggested that the heavy concentration of salt in some kimchi and the fish sauce used for flavoring could be problematic, but they too have received comparatively little attention."
"Historically, gastric cancer has been one of the major cancers in East Asian countries like Korea and Japan. Although the mortality and incidence of gastric cancer has decreased in these regions, gastric cancer is still the fourth most common cancer in the world and the second most common cancer in Asia."
"In a study on the population-attributable fraction of infectious agents in Korean population, H. pylori infection was responsible for 80.3% of non-cardia gastric cancers in men and 78.7% in women."
"Men who smoked for 20~39 years had a 2.09-fold increased risk of gastric cancer compared to non-smokers, and those who smoked for more than 40 years had a 3.13-fold increased risk."
"The average daily salt intake in the Korean population was 13.4 g in 2005, whereas the daily intake recommended by the World Health Organization is less than 5 g."
"Nitrates used as preservatives in processed meats are also produced endogenously in gastric acid. These contribute to N-nitroso compound production, which are suspected carcinogens. In addition, high-temperature cooking of meat generates mutagens such as heterocyclic amines and polycyclic aromatic hydrocarbons. Charcoal grilled beef or broiled meat and fish consumption were associated with an increased risk for gastric cancer, whereas total meat consumption was not associated with gastric cancer risk in case-control studies."