A 2024 meta-analysis found that ochratoxin A (OTA), a toxic compound produced by mold, was detected in 58 percent of coffee products worldwide. This heat-stable mycotoxin survives the roasting process and transfers directly into your brewed cup at rates between 74 and 86 percent. For people who drink two to four cups daily for decades, understanding this contamination matters more than most realize.

Why Does Mold Grow in Coffee Beans?

Coffee beans are a natural breeding ground for fungal growth. The primary mycotoxins of concern are ochratoxin A and aflatoxin B1, both produced by Aspergillus and Penicillium species of mold. These fungi thrive in the warm, humid conditions common to coffee-growing regions in Central America, South America, Africa, and Southeast Asia.

A 2024 systematic review published in Food Additives and Contaminants analyzed over 3,250 coffee samples worldwide and found that OTA was detected in approximately 55 percent of all samples tested. The prevalence varied dramatically by country of origin, ranging from 7.5 percent to 100 percent depending on the region.

What makes this especially concerning is the nature of the toxins themselves. OTA is classified as nephrotoxic, meaning it causes kidney damage, and has been classified by the International Agency for Research on Cancer (IARC) as a Group 2B possible human carcinogen. Aflatoxin B1, the other primary mycotoxin of concern, is classified as a Group 1 known human carcinogen by IARC.

How Much Mycotoxin Actually Makes It Into Your Cup?

While roasting destroys a significant portion of mycotoxins, studies estimate 65 to 80 percent reduction depending on roast level. However, OTA is notably heat-stable and survives the roasting process more effectively than other mycotoxins. Research has confirmed that 74 to 86 percent of the OTA present in roasted coffee transfers directly into the brewed beverage.

This is where cumulative exposure becomes relevant. A single cup of coffee contains a relatively small amount of OTA. The concern is not acute toxicity from one cup, but bioaccumulation over years of daily consumption. Because OTA does not break down in the body, it accumulates in the kidneys, liver, and bones over time.

Decaf drinkers face an additional risk. Caffeine is a natural antifungal compound. When caffeine is removed during the decaffeination process, the beans become more susceptible to mold growth during storage and handling. This makes third-party testing even more important for decaf products.

What Other Contaminants Are Found in Coffee?

Mycotoxins are not the only concern. Coffee plants absorb minerals from the soil in which they grow, and that includes heavy metals such as lead, cadmium, arsenic, and mercury. The specific metals present in any given coffee depend largely on the geographic region, the volcanic or industrial history of the soil, and whether synthetic fertilizers or pesticides containing metal compounds have been used.

A 2025 study conducted by the Clean Label Project tested 57 coffee products from 45 top-selling brands, running over 7,000 individual tests for contaminants including lead, cadmium, arsenic, mercury, mycotoxins, pesticides, phthalates, and glyphosate. The study confirmed that heavy metal concentrations varied significantly by growing region, with Hawaiian coffees showing the highest levels due to volcanic soil and African coffees showing some of the lowest.

A 2021 study in the journal Molecules analyzed cadmium and lead in 23 natural coffee samples and found that while individual cup exposure was low (less than 2 percent of the tolerable weekly intake), 94 to 95 percent of the metals present in the grounds transferred into the brewed cup.

How Are Pesticides Used in Coffee Production?

Coffee is one of the most heavily sprayed crops in the world. Because it is predominantly grown in tropical regions where pest and fungal pressure is high, conventional coffee production relies on a wide range of chemical inputs. Among the most commonly used pesticides in coffee cultivation are chlorpyrifos, endosulfan, cypermethrin, glyphosate (Roundup), and various copper-based fungicides.

Chlorpyrifos is an organophosphate insecticide that has been banned in the United States and the European Union for household use due to its neurotoxic effects, but it is still used on coffee plantations in many producing countries. A 2022 review published in Frontiers in Nutrition documented its presence in coffee samples from Brazil and other major producing nations. Endosulfan, a highly toxic organochlorine insecticide, has been banned in most countries but continues to be used in some coffee-producing regions.

Steps to Reduce Your Exposure to Coffee Contaminants

• Seek Third-Party Testing: Look for coffee brands that conduct independent laboratory testing for mycotoxins, heavy metals, pesticide residues, and other contaminants. Third-party verification provides assurance that testing was conducted by an unbiased organization rather than the brand itself.
• Choose Organic Certification: Organic coffee is grown without synthetic pesticides and fertilizers, reducing exposure to chlorpyrifos, endosulfan, and other chemical inputs used in conventional production. Certification from recognized organic bodies provides documented compliance with these standards.
• Select Water-Based Decaf Options: If you drink decaf, choose brands that use the Swiss Water Process or equivalent water-based decaffeination methods rather than solvent-based processes. Water-based methods avoid additional chemical exposure while decaf beans are already more vulnerable to mold contamination.
• Verify Heavy Metal Testing: Ask brands for documentation showing low or undetectable levels of lead, cadmium, arsenic, and mercury. Geographic origin matters; coffees from regions with lower volcanic activity and less industrial history tend to have lower heavy metal concentrations.
• Research Brand Transparency: Reputable brands publish their testing results and can explain their sourcing practices, growing regions, and quality control measures. Transparency about testing protocols and results is a strong indicator of commitment to clean products.

For people who drink two to four cups of coffee per day, every day, for decades, choosing a brand that tests for and documents low or undetectable levels of contaminants is a reasonable precaution. The cumulative exposure to heat-stable mycotoxins and bioaccumulating heavy metals over a lifetime of daily consumption justifies the extra attention to product quality.