Can Kombucha Mold Cause Cancer?

Someone asked about the potential risks of kombucha tea on Microbial Nutrition recently, citing an anecdotal report of a woman who developed pancreatic cancer after a year of drinking kombucha tea. It would be difficult to prove any causal relationship, but Bruce Stordock did post a warning about a source of carcinogens from a web page:

High acidity of the broth aside, I have seen several of my vessels spontaneously contaminate with molds. Of most concern are the species of Aspergillus I have found floating around with Kombucha. I fear that amateurs could think that by merely pulling out the Aspergillus colonies with a fork, that the culture would be de-contaminated, a dangerous, even deadly presupposition.

The water-soluble toxins of Aspergillus can be highly carcinogenic. Several species are known killers. Since the public can not be expected to distinguish a clean fermented culture from one which is not, I fear that the unreserved use of this tea will result, has resulted in illness, if not death. (See Newsweek, April 25th, 1995, pg. 6.)

(source: http://www.fungi.com/info/articles/blob.html)

At first glance, this is alarming because it implies that a culture that is supposed to be healthy could be causing great harm. However, a further look at Aspergillus does not seem to bear out these concerns.

Aspergillus is a genus representing about 200 different species of mold. Of these species, Aspergillus flavus and Aspergillus fumigatus are known to cause invasive infections in humans. Aspergillus fumigatus and clavatus are also commonly sources of allergic reactions in humans. And a type of mycotoxin called aflatoxin produced by some strains of Aspergillus flavus and Aspergillus parasiticus have been linked to cancer. (See also The Aspergillus Website which has information on Aspergillus-caused illnesses and case histories. Note that the organization is funded by pharmaceutical companies.)

In kombucha cultures, Aspergillus niger and Penicillum notatum were the most common molds found in a survey of cultures:

According to Michael Roussin, Director of the Kombucha Consumer Research Group in Salt Lake City, the two most often found molds on Kombucha are: Penicillum notatum and Aspergillus niger. Mr. Roussin's group of researchers tested many hundreds of Kombucha colonies during 1996, and during this time found that these two molds were the two they isolated from the tested colonies. According to them, Penicillum notatum is the green mold and Aspergillus niger is commonly white, black or gray.

Unfortunately, the full report containing the comprehensive list of moulds is not available for free.

Aspergillus niger is "generally regarded as safe" by the FDA, however it is dangerous to immuno-compromised people, and you should avoid breathing the spores:

A niger is the third most common Aspergillus species to cause pulmonary disease, after Aspergillus fumigatus and Aspergillus flavus. It is also a rare cause of chronic necrotizing pulmonary aspergillosis. A fermentation by-product of Aspergillus fungi, especially A niger, is oxalic acid, which complexes with calcium from the host to form calcium oxalate crystals. These crystals cause severe tissue necrosis, including damage to blood vessels.

However, I could not find any confirmed reports of other pathological species of Aspergillus in kombucha. An FDA "Talk Paper" mentions Aspergillus, but not any specific species:

The unconventional nature of the process used to make Kombucha tea has led to questions as to whether the product could become contaminated with potentially harmful microorganisms, such as the mold Aspergillus. Such contamination could produce serious adverse effects in immune-compromised individuals.

On the other hand, some species of Aspergillus are necessary for certain fermented products. For example Aspergillus sojae and Aspergillus oryzae are used to make koji and its derivatives which include miso and amazake (a sweet type of sake). Dom mentions that A. oryzae is one of the molds in sourdough starter as well.

Finally, going back to the originally posed question, kombucha just doesn't agree with some people, as Heidi notes:

People tend to react to kombucha either positively or not. On another list, several people got candida-like reactions after imbibing it. Others felt wonderful. I got some almost-migraine like symptoms once after a big glass. A fair number of people get a "niacin flush" after drinking it. There have been issues about it not getting along with certain medications (which is also true of grapefruit, BTW!).

Being exposed to carcinogenic molds does not look like one of the risks involved with making kombucha, especially if hygienic practices are followed.