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'''Mold''' (US) or '''mould''' (UK) are multicellular fungi that grow in the form of filaments called ''hyphae'' that appear like long branch-like structures under a [[microscope]]. Although not a taxonomic designation, there are an estimated 10,000 - 300,000 of species of molds that live in a wide variety of environments <ref name="usda">[http://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/safe-food-handling/molds-on-food-are-they-dangerous_/ct_index "Molds On Food: Are They Dangerous?" United States Department of Agriculture. Retrieved 07/15/2016.]</ref>. In general , they cause biodegredation biodegradation of foods and other natural materials (such as wood in buildings), which has a wide role of effects depending on the species of mold. For example, some species of mold can be the cause of food spoilage, and other species play an important role in food production such as in cheese and soy sauce production <ref name="wikipedia_mold"></ref>. Certain species of mold are thought to contribute precursors that effect affect flavor production in the toasting of oak barrels <ref>[http://www.demptos.fr/en_v2/images/J_SCI_TECH_TONNELLERIE_064_A.PDF The duration effect of natural seasoning of Quercus petraea Liebl. and Quercus robur L. on the diversity of existing fungi flora and some aspects of its ecology. N. Vivas. 1996.]</ref> Molds have also been used in the pharmaceutical industry to produce antibiotics and other medicines. Certain molds can cause allergic reactions as well as diseases from mold growth within the body or from mycotoxin production in exposed foods or from breathing spores from mold growth in buildings <ref name="wikipedia_mold">[https://en.wikipedia.org/wiki/Mold Mold. Wikipedia. Retrieved 07/12/2016.]</ref>.  There are many discussions about identifying mold and what to do about mold if it grows in beer in the [https://www.facebook.com/groups/MilkTheFunk/search/?query=mold Milk The Funk Facebook group]. Please read this wiki page and search the MTF Facebook group for previous posts about mold before posting a question about it so that we can limit the number of repetitive posts about mold ([https://www.facebook.com/groups/MilkTheFunk/search/?query=mold click here] to do a search; must be a member of the MTF Facebook group).

Although little studying has been done on mold growth in beer, it has been known to occur in barrel aged beers are fruited sour beers. Oxygen generally needs to be present in order for mold to grow. Mold growth on fruit that is in sour beer can occur if the fruit is floating above the surface of the beer, and enough oxygen is present (either from vacuum suck-back, the oxygen permeability of the vessel, or sampling). For this reason, many commercial sour brewers will "punch down" the fruit frequently with a dish-like tool. ===Mold Growth in Wild Mead===It has been demonstrated that while honey is antimicrobial due to its high sugar concentration and low water concentration, which inhibits the growth of microbes, honey is not inherently pasteurized or sanitary. Low levels of molds, yeasts, and spore-forming bacteria can survive in honey and can begin to grow once the honey is diluted with water as it is in mead-making. Honey can start to ferment when it contains as little as 17% water, and at 19% water honey is very likely to ferment. It is thought that most of the microbes found in finished honey originate from the handling of the honey, and do not originate from the hive, although some microbes may be introduced from the bees <ref>[https://www.sciencedirect.com/science/article/pii/0168160596009701 Microorganisms in honey. Jill A Snowdon, Dean O Cliver. International Journal of Food Microbiology. Volume 31, Issues 1–3, August 1996, Pages 1-261996.]</ref><ref>[http://journals.tubitak.gov.tr/veterinary/issues/vet-13-37-5/vet-37-5-20-1301-46.pdf Microbiological and parasitological quality of honey produced in İstanbul. Emek DÜMEN, Hayrettin AKKAYA, Gülay Merve ÖZ, Funda Hatice SEZGİN. 2013.]</ref>, including botulism spores that can cause death to infants under 12 months old <ref>[http://jfoodprotection.org/doi/pdf/10.4315/0362-028X-44.11.812?code=FOPR-site Incidence and Origin of Clostridium botulinum Spores in Honey C. N. HUBTANEN, D. KNOX, and B. SBIMANUK. 1981.]</ref><ref>[https://www.mayoclinic.org/healthy-lifestyle/infant-and-toddler-health/expert-answers/infant-botulism/faq-20058477 "Infant and toddler health". Jay L. Hoecker, M.D. Mayo Clinic website. May 15, 2018. Retrieved 09/20/2018.]</ref>. While normal mead making procedures limit the potential of mold growth due to pitching healthy yeast and a fast start to fermentation, it is possible that mold growth can occur when attempting to ferment mead spontaneously by not adding any laboratory yeast because of the lag time for fermentation to begin <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/2140692022625667/ Adam Johnson. Milk The Funk Facebook group post on preventing mold growth. 06/21/2018.]</ref>. To prevent mold growth during spontaneous fermentation of mead (also known as "wild fermentation" or "native fermentation"; see [[Mead#Alternative_Fermentation_Techniques|Mead]]), purging the vessel with CO² until the mead begins actively fermenting should help reduce the chances of mold growth. Lowering the pH to 4.5 will also help prevent mold growth, as well as a starting gravity at or below 1.070 because higher gravity must takes longer to start fermentation, which gives more opportunity for mold to grow before fermentation begins <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/2140692022625667/?comment_id=2142696379091898&reply_comment_id=2144309682263901&comment_tracking=%7B%22tn%22%3A%22R8%22%7D Justin Amaral. Milk The Funk group thread on mold in spontaneously fermented mead. 06/23/2018.]</ref>. See also:* [[Mead#Spontaneous|Microbes found in honey.]]

* If aging sour beer on whole fruit, use a punch-down tool frequently so that the alcohol and low pH kills any mold that might be present before it begins to grow. CO² may be helping the fruit to float, and punching-down the fruit will help to release that CO². Homebrewers can gently swirl their carboys to accomplish the same thing. Purging the headspace with CO² will also help prevent mold growth.

A small number of molds can produce mycotoxins, which are poisonous substancescalled mycotoxins, or aflatoxins, which are cancer-causing poisonscalled aflatoxins. Some molds that do not produce toxins can still cause allergic reactions or respiratory problems <ref name="usda"></ref>. Their effects can be accumulativeare cumulative, rather than immediately toxic as in the case of pathogenic bacteria. A small amount of ingested mycotoxin won't be harmful right away, but it will increase the risk of gastric, intestinal, and colon cancer, as well as other health issues <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/2137444642950405/?comment_id=2137519622942907&reply_comment_id=2137542839607252&comment_tracking=%7B%22tn%22%3A%22R2%22%7D Dr. Bryan Heit Heit. Milk The Funk Facebook group thread on the health risks of mold. 06/19/2018.]</ref>. As a general rule of thumb, pigmented molds (non-white/grey) are more likely to produce poisonous substances (especially black mold which could be ''Aspergillus''), however , there are exceptions to this rule guideline <ref name="Dr. BryanHeit">[http://suigenerisbrewing.blogspot.com/2016/08/fact-or-fiction-can-pathogens-survive.html "Fact or Fiction? Can Pathogens Survive in Beer - Mould Edition." Dr. Bryan Heit of Sui Generis Blog. 08/11/2016. Retrieved 08/11/2016.]</ref>. Some mycotoxins can survive boiling temperatures in wort to varying degrees, so if mold develops during processes such as kettle souring, it is possible for some percentage of mycotoxins to survive the wort boiling process and fermentation (one study showed that 20-30% of two mycotoxins were removed during boiling and fermentation) <ref>[http://www.sciencedirect.com/science/article/pii/S0168160507003984 Stability of mycotoxins during food processing. Lloyd B. Bullerman, Andreia Bianchini. 2007.]</ref>. Only mold that is growing in contact with the beer itself is considered potentially dangerous; mold growing in airlocks or outside of vessels should not be a cause for concern as long as they do not come into contact with the beer itself. If only a small amount of mold has grown on the beer, then removing it quickly and purging the vessel with CO² to prevent more mold growth will limit the potential for exposure to toxins. However, if a large amount of mold has grown and if it happens to be a mycotoxin-producing species, then there is a higher chance that more toxin could be in the beer <ref name="Dr. Bryan Heit" />. Identifying mold based on what it looks like is not a reliable way to determine if a mold is a cause of concern for health <ref name="Dr. Bryan Heit"></ref>. There are [https://www.google.com/search?client=firefox-b-1&ei=Ww08W-fWOabX0gK73K6YBg&q=mold+testing+lab&oq=mold+testing+lab&gs_l=psy-ab.3..0l2j0i20i263k1l2j0l6.127585.128971.0.129112.16.14.0.0.0.0.181.1496.0j12.12.0....0...1c.1.64.psy-ab..4.12.1491...0i67k1j0i131k1j35i39k1j0i131i20i264k1j0i20i264k1.0.5QReSMbR0GU mold testing labs] that are available that might be able to identify whether the mold is toxic or not. If mold is present in beer, commercial breweries should remove the mold and send it to a lab to check if it is a toxic mold before allowing the beer to be consumed. Some homebrewers may decide to risk taking a chance that the mold will not cause illness, however, we recommend discarding beer that has come into contact with the mold, especially if serving to others. Soft fruits and vegetables with high moisture that grow mold on the surface can also be contaminated with mycotoxins or aflotoxins below the surface, therefore beer or wort that has mold growing on its surface could also be contaminated below the surface <ref name="usda"></ref>.

Identifying See these resources on mold based and mycotoxin:* [https://www.who.int/news-room/fact-sheets/detail/mycotoxins Mycotoxins key facts from the World Health Organization.]* [http://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/safe-food-handling/molds-on what it looks like is not a reliable way to determine if a mold is a cause -food-are-they-dangerous_/ct_index USDA website.]* [https://www.intechopen.com/online-first/80725 "Implications of concern for health <ref name=Mycotoxins in Food Safety,"Bryanby Dr.Ing. Romina Alina Marc in "Mycotoxins and Food Safety - Recent Advances" (sepcifically section "></ref>3. If mold is present 10 Mycotoxins in beer, it might be possible for commercial breweries to remove the mold and send it to a lab to check if it is a toxic mold before allowing the beer to be consumed").]* [http://ucfoodsafety.ucdavis.edu/files/26438.pdf UC Davis Food safety sheet.]* [http://suigenerisbrewing.blogspot. Some homebrewers may decide to risk taking a chance that the mold will not cause illness, however we recommend discarding beer that has come into contact with mold, especially if serving to others (mold growing on SOFT fruits and vegetables with high moisture content com/2016/08/fact-or-fiction-can be contaminated below the surface <ref name=-pathogens-survive.html "usdaFact or Fiction? Can Pathogens Survive in Beer - Mould Edition.,"></ref>)by Dr. Bryan Heit of Sui Generis Blog. ]

See the MTF threads:* [httphttps://www.fsisfacebook.usda.gov/wps/portalcom/fsisgroups/topicsMilkTheFunk/food-safety-educationpermalink/get-answers2861420423886153/food-safety-fact-sheets/safe-food-handling/molds-Discussion on-food-are-they-dangerous_/ct_index USDA website], [http://ucfoodsafety.ucdavis.edu/files/26438.pdf this UC Davis Food safety sheet], and [http://suigenerisbrewing.blogspot.com/2016/08/fact-whether or-fiction-not mold can-pathogens-survive.html "Fact penetrate wood barrels or Fiction? Can Pathogens Survive cracks/leaks in Beer - Mould Editionbarrels from the outside.," by Bryan of Sui Generis Blog] for more information on the health concerns of mold that grows on food.

As mentioned above, identifying the species of mold based on what it looks like with the naked eye is not a reliable way to identify it at the species level, and thus not a reliable way to know if the mold growth is safe. It isAvoiding the potential risk of mold growth can be somewhat eliminated by visually inspecting the growth and determining if it might be mold growth and pellicle or yeast growth. Visual inspection, however, usually easy may not be enough to tell the difference between general identify whether or not mold growth and is completely absent or not on a pellicle or otherwise, especially for vessels such as barrels which may have more exposure to oxygen at the surface and headspace. Molds can have a similar appearance to yeast/bacteria pellicles to the naked eye. Microscopy is the most accurate way to determine if growths are mold vs yeast growthor bacteria (see [https://suigenerisbrewing.com/index.php/2023/10/20/beer-and-mould "Beer and Moulds – More There Than You Think" by Dr. Bryan Heit] for more information). Mold tends Many molds tend to look "fuzzy" or "hairy" and often has green, red, black, white, or grey colors, where as whereas yeast activity or pellicles tend to have evidence of CO2 production (bubbles), and looks look "creamy", "powdery", or "chalky" and is never green, red, or black in color(unless there is material in the beer that is discoloring the pellicle, such as fruit). Mold tends to grow in isolated spots on the surface, while yeast pellicles tend to grow throughout the surface. Sometimes the pellicle is not a solid pellicle, but instead just scattered across the surface in a spotty yet more widely distributed manner compared to mold which would grow in a more isolated area. Protein/carbohydrate coagulation can also be misidentified as mold, however , this also never appears "hairy" or "fuzzy" like mold. We recommend taking a picture through a hand lens when posting an image of what might be mold as this will make it easier to identify. Be sure that the color of the mold/pellicle in the photo is accurate to what it looks like with the naked eye (sometimes cameras make white substances appear more pigmented, which can throw off attempts to identify the organism online). Please make an attempt to identify whether the growth is mold or not on your own before posting in the group (these types of posts clog the stream!). See the images below for examples that should help. Mold can be removed and sent to a [https://www.google.com/search?client=firefox-b-1&ei=Ww08W-fWOabX0gK73K6YBg&q=mold+testing+lab&oq=mold+testing+lab&gs_l=psy-ab.3..0l2j0i20i263k1l2j0l6.127585.128971.0.129112.16.14.0.0.0.0.181.1496.0j12.12.0....0...1c.1.64.psy-ab..4.12.1491...0i67k1j0i131k1j35i39k1j0i131i20i264k1j0i20i264k1.0.5QReSMbR0GU mold testing lab] to possibly be identified as toxic or benign.   

The following table shows examples of mold or pellicles from the Milk The Funk Facebook group, and the consensus on whether mold is likely present or not based on the image.Note that it is likely that barrel aged beer with pellicles can also contain at least some mold. It is not possible to determine whether mold is present or not based only on visual inspection; lab analysis is required to determine for sure if mold is present or not <ref>[https://www.mdpi.com/2311-5637/7/3/174 Piraine REA, Leite FPL, Bochman ML. Mixed-Culture Metagenomics of the Microbes Making Sour Beer. Fermentation. 2021; 7(3):174. https://doi.org/10.3390/fermentation7030174.] See also [https://www.facebook.com/groups/MilkTheFunk/posts/7494013197293496/?comment_id=7495644597130356&reply_comment_id=7495757290452420 this MTF post by Dr. Bryan Heit]</ref>.  Also, search the [https://www.facebook.com/groups/MilkTheFunk/search/?query=mold Milk The Funk Facebook group] for examples of identifying mold versus yeast activity.

* [http://suigenerisbrewing.blogspot.com/2016/08/fact-or-fiction-can-pathogens-survive.html "Fact or Fiction? Can Pathogens Survive in Beer - Mould Edition.," by Dr. Bryan Heit of Sui Generis Blog.]