Mold

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Mold is a type of fungus. It appears on surfaces as fuzzy or hairy patches and may be colored as white, gray, green, red, or black.

Wild mold growth is a health hazard because it can produce allergens and toxins, some of which are carcinogenic. Therefore if there is any mold growth on your batch, all of it should be dumped, carefully (to avoid spreading more spores).

The one exception to this is when a domesticated mold culture is used intentionally, such as with Sake, rice wine, or some cheeses.

Prevention

Mold can generally be prevented in beer by oxygen avoidance and pitching healthy yeast. In wine, pitching healthy yeast, punching down fruit, sulfite usage, and stabilization can all help prevent mold growth.

Reducing open air exposure goes a long way toward lessening mold spores and therefore reducing the risk of mold growth. To prevent mold growth while allowing oxygen exposure (such as needed for kombucha production), loosely covering the vessel with foil is a good option, or using an airlock with a HEPA filter.

See Contamination for more info.

On malt

Alternaria, Cladosporium, and Fusarium tend to invade the grain in the field, whereas Aspergillus, Penicillium, and Rhizopus can develop significantly during grain storage.

Fungi (e.g., Fusarium) can release mycotoxins such as trichothecenes (e.g., deoxynivalenol, DON) and zearalenone. DON is associated with Fusarium infection,21,23 and its presence is linked with “beer gushing.” Aspergillus produces aflatoxins and ochratoxins. Mycotoxins are associated more with maize than barley and can be dangerous to the health and life of animals; aflatoxins from Aspergillus are potentially hazardous. In animals, the mycotoxin zearalenone is an estrogenic and tumor-producing toxin. Although zearalenone (less than 2.0 ppb) has been found in fermenting worts and would have been extracted from mashed cereals, it is changed to α-zearalenol during fermentation. The latter compound is more of a threat to human health than zearalenone. The levels of harmful fungi on malting barley are normally very low and should not be harmful to humans that drink beer. In contrast, spent grains from the mash tun can have concentrated levels of mycotoxins, especially if stored wet. However, spent grains can be detoxified using specified levels of formaldehyde or by ammoniation, before being fed to farm animals. Toxins from Ergot infections are dangerous to human health and can cause nervous diseases.

Myths

Myth: The beverage will be OK if you just scrape off the mold patches.
Truth: Mold is by definition filamentous. It sends out hyphae, or "roots" in laymen's terms, and it can secrete allergens, toxins, and carcinogens that would be impossible to separate from the liquid/culture. Carcinogens wouldn't get you sick immediately, so you wouldn't even necessarily know you're ingesting them.

Myth: Small amounts of mold may be OK.
Truth: We generally recommend avoiding the health risk, as does the USDA: "Microbiologists recommend against scooping out the mold and using the remaining [soft food]."

It's impossible for us to quantify how much mycotoxin or allergens may be present. Some people have life-threatening reactions to penicillin for example, which could trigger with a very small amount.

There are a wide variety of possible mold toxins and they have negative health impacts even in small amounts.

Home brewers have experienced serious illness from brewing with moldy grain.

See also

• http://www.milkthefunk.com/wiki/Mold
• Contamination

Potential sources

• https://repositori.udl.cat/bitstream/handle/10459.1/60356/026053.pdf?sequence=7&isAllowed=y
• https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/molds-fungi
• https://www.sciencedirect.com/topics/engineering/mould-growth
• https://homebrewacademy.com/how-to-fix-mold/