Is it true that most coffee is contaminated with mold?

Answer:

Coffee beans, like many other agricultural crops and foods (oats, corn, peanuts, rice, wheat, cocoa, grapes etc.) are susceptible to contamination with mold. While some molds are harmless, others can produce substances called mycotoxins, which can be harmful. Of most concern in crops such as coffee beans are the mycotoxins ochratoxin A (OTA) and aflatoxin B1. However, as explained below, amounts found in roasted and brewed coffees do not appear to pose a health risk. In fact, you may be exposed to more of these mycotoxins from eating other common foods.

Ochratoxin A (OTA)
OTA may be harmful to the kidneys, and is classified as a possible human carcinogen by the World Health Organization (IARC Monograph 2015 -- accessed from IARC Evaluation of Carcinogenic Risks to Humans). There is no current FDA limit for OTA in foods in the U.S. but the European Food Safety Authority (EFSA) has established a limit of 5 mcg/kg for roasted coffee and 10 mcg/kg for instant coffee (Fapohunda, Basic Res J Agric Sci Rev 2014; EFSA Panel on Contaminants in the Food Chain, EFSA J 2010; International Coffee Organization 2005).

Much of the concern about mold in coffee comes from a frequently cited study that found 91.7% of green coffee bean sampled (Coffea arabica from Brazil) to be contaminated with mold (Martins, Food Addit Contam 2003). However, it is important to note more than half the samples tested did not contain OTA -- only 33% were found to be contaminated with OTA, and of these, half contained levels between 0.2 and 1 mcg/kg (well below the European limit of 5 mcg/kg for OTA in roasted coffee). In addition, these beans were not roasted, which has been shown to reduce the amount of OTA in coffee by between 30% to 90% (Fapohunda, Basic Res J Agric Sci Rev 2014).

Although one very small study found that ground roasted coffee retained between 22 and 66% of its OTA after brewing (Malir, Toxins 2014), amounts in final coffee products have still been found to be well below EU limits. In a study of 633 roasted, ground and instant coffee products commercially available in European markets, the average amount of OTA in roasted and ground coffee was only 0.8 mcg/kg and drinking four cups of coffee per day for a week would contribute less than 2% of the EU's tolerable weekly intake (Stegen, Food Addit Contam 1997). In comparison, it is estimated that people in Europe are exposed to 10 times that amount of OTA from weekly consumption of cereals.

Similarly, a study by the website Mamavation of 12 organic and premium roasted coffees purchased in the U.S. between January and May 2024 found that none contained detectable mycotoxins (including ochratoxin A, aflatoxin B1, and other aflatoxins), mold or yeast. Coffee brands tested included Bulletproof, Danger, Death Wish, Equal Exchange, Isagenix, Lifeboost, Peet's, Purity, Scout & Cellar, Subtle Earth, and The Bean Coffee Company.

Another study that analyzed 295 different coffee samples — 206 of which were green coffee beans and 89 of which were roasted coffee — from supermarkets, shops or bazaars in Saudi Arabia found that only 4 (4.5%) samples of roasted coffee beans had detectable levels of OTA. Among the roasted coffee bean samples that did contain OTA, the average concentration was below the maximum limit of 5 mcg/kg (average: 3.4 mcg/kg), although one sample contained OTA levels above this limit — 5.6 mcg/kg. Although the percentage of green coffee samples that contained OTA was low (13.5%), those that did contain this toxin had levels that were higher than what was found in roasted coffee (average 7.3 mcg/kg; range 1.2 to 50 mcg/kg) (Almasoud, JSFA Reports 2022).

Aflatoxin B1
Aflatoxin B1 is classified as a human carcinogen by the World Health Organization (IARC Monograph 2015 -- accessed from IARC Evaluation of Carcinogenic Risks to Humans). The FDA limits the amount of total aflatoxins (including aflatoxin B1 and others) in most foods to 20 mcg/kg (FDA Compliance Policy Guidance Manual 2014). One study of arabica and robusta varieties of ground coffees that were stored in humid conditions for 30 days found the aflatoxin levels to vary, ranging from 0.000094 to 0.002086 mcg/kg -- all well below the FDA's limit (Al-Abdalall, Can J Pure Appl Sci 2014).

As with OTA, roasting coffee beans significantly reduces the amount of aflatoxin B1, by an estimated 50 to 100%, and brewing coffee in a coffee maker appears to further decrease aflatoxin B1 that remains after roasting (Soliman, J Agric Food Chem 2002; Micco, Myctoxin Res 1992). One study of roasted coffee which had been artificially contaminated with aflatoxin B1 found brewing reduced the aflatoxin B1 that remained after roasting by up to 99%, depending on which type of coffee maker was used (Micco, Myctoxin Res 1992).

Overall, the risk of exposure from mycotoxins in coffee appears to be low, as they are significantly reduced during processing and roasting and brewing and have been found to be well below guidelines set by agencies like the EFSA and/or FDA. If you want to further reduce your exposure, however, it is interesting to note that caffeinated coffee may contain lower levels of aflatoxin B1 than decaf and that regular ground coffee was found to contain lower amounts of OTA than instant (Soliman, J Agric Food Chem 2002; Stegen, Food Addit Contam 1997).

Additionally, remember to clean your coffee maker to avoid mold in your coffee. According to a study by NSF International, coffee maker reservoirs are among the top five "germiest" items in a household, found to be more contaminated with yeast, mold and bacteria than bathroom doorknobs and light switches (NSF 2011). It is also important to remove used coffee pods from machines shortly after you've made your cup, as the wet coffee grounds in the pods can lead to the formation of mold. Similarly, using pods that have been punctured or exposed to significant moisture may increase the risk that the pods may contain mold or bacteria. However, according to a coffee manufacturer, using intact pods a couple months after the "best before" date is unlikely to increase the risk of mold in coffee if the pods have been stored in a cool, dry area — although the coffee might not taste as fresh.

Note: There do not appear to be any studies of mycotoxins in supplements made with green coffee bean extract. While the beans are not roasted before extraction, the extraction process itself may eliminate mold. Some brands of green coffee bean extract, such as Svetol® do set a limit for total yeasts and molds (unspecified) in the extract, although this is not required by federal regulations.