Coffee is a daily ritual for millions, but concerns about mold have led many to question its safety. The actual danger comes not from visible mold but from specific toxic byproducts that certain fungi produce. Understanding the source of these compounds, known as mycotoxins, is the first step in addressing this concern.
Defining the Contaminants in Coffee
The compounds of concern in coffee are mycotoxins, naturally occurring toxins produced by various molds or fungi. These toxins form when fungi, such as species from the Aspergillus and Penicillium genera, grow on crops like coffee beans under favorable conditions. The two mycotoxins most relevant to coffee are Ochratoxin A (OTA) and Aflatoxin B1.
Ochratoxin A is a byproduct of fungi like Aspergillus ochraceus and Penicillium verrucosum, and is the most frequently discussed mycotoxin in coffee. Aflatoxin B1 is produced by Aspergillus flavus and is considered one of the most toxic naturally occurring carcinogens known.
Assessing the Health Implications of Exposure
Exposure to these mycotoxins at high levels can cause serious health issues, but the actual risk from commercially available coffee is low. Ochratoxin A has been linked to nephrotoxicity, which is damage to the kidneys, and is classified as a possible human carcinogen. Aflatoxin B1 is a known carcinogen associated with liver damage. However, the liver is capable of neutralizing mycotoxins, preventing them from building up in the body when exposure remains low.
Regulatory bodies worldwide monitor mycotoxin levels to ensure food safety, with over 100 countries setting standards. The European Union (EU) has some of the strictest limits for OTA in roasted and ground coffee. The United States Food and Drug Administration (FDA) monitors mycotoxins but does not currently have a specific federal limit for OTA in coffee. Studies have shown that exposure levels, even for heavy coffee drinkers, are significantly below the maximum safe limits set by international organizations.
Roasting the coffee beans provides an additional safety barrier, as the high temperatures can reduce Ochratoxin A levels by 70% to 90%. The brewing process further dilutes any remaining toxins, making the final beverage generally safe. The most significant risks are often found in low-grade coffee intended for internal consumption in producing countries, where legal controls may be reduced or nonexistent.
From Bean to Brew: Points of Contamination
Mycotoxin contamination can occur at multiple stages, beginning in the field where the coffee cherries are grown. Fungi thrive in the warm, humid conditions common in coffee-growing regions, making the crop susceptible to contamination. If the coffee cherries fall to the soil and are not promptly harvested, the beans are more likely to be contaminated.
Improper drying is considered the most common cause of mycotoxin presence. Beans must be dried quickly to a specific moisture content, typically between 10% and 12.5%; if they remain too damp, mold growth is encouraged. Contamination can increase during storage and transport if the green beans are kept in humid, poorly ventilated conditions. Even after processing, contamination can happen at home in poorly maintained brewing equipment, such as water reservoirs or grinders, where wet, discarded grounds can become a breeding ground for mold spores.
The method used to remove the fruit from the bean also affects contamination risk. Wet-processed, or washed, coffees generally exhibit lower levels of mycotoxins compared to dry-processed, or natural, coffees. This difference is likely due to the prolonged contact with the fruit and fermentation that occurs during the dry processing method.
Mitigating Risk Through Selection and Preparation
Consumers can take practical steps to reduce mycotoxin exposure by making informed choices about selection and storage. Choosing specialty-grade coffee that has been wet-processed may lower the initial risk compared to naturally processed beans. Beans grown at higher altitudes are also often exposed to cooler temperatures, which helps inhibit mold growth.
Practical Mitigation Steps
- Store coffee in an airtight container in a cool, dry place to prevent moisture absorption.
- Grind whole beans at home just before brewing, as pre-ground coffee has a larger surface area exposed to air, raising contamination risk.
- Regularly clean all brewing equipment, especially the water reservoir and grinder, to eliminate any developed mold.