Coffee Education

Search this topic and you will find two loud camps. One sells the idea that your morning cup is quietly poisoning you. The other waves the question away as internet nonsense. Neither is accurate, and the second is nearly as unhelpful as the first.

What follows is what the regulators and the published research actually say, including the parts that are less convenient.

The Short Answer

Yes, mold can grow on coffee, almost always on green beans before roasting. Certain molds produce mycotoxins, and the one that matters for coffee is ochratoxin A. It is regulated in the European Union, it is monitored across the supply chain, and the levels found in commercially traded roasted coffee are typically well under the legal maximum.

How Mold Gets Into Coffee

The risk window is at origin, not in your kitchen. Coffee arrives as a fruit, and the seed has to be separated from it and dried down to a stable moisture level, usually around 10 to 12 percent. Between the picking and the drying, the crop is warm, wet, and organic, which is exactly what mold prefers.

Three points carry most of the risk:

• Drying. Coffee dried too slowly, or rewetted by rain partway through, gives mold time to establish.
• Storage at origin. Beans held above safe moisture in a humid warehouse can develop mold months after harvest.
• Transit. Condensation inside a shipping container can rewet a lot that left the farm in good condition.

This is why moisture content is a standard contract term in green coffee buying, and why buyers reject lots above roughly 12.5 percent. It is a food safety control before it is a quality control.

What Roasting Actually Does

Roasting takes beans well past 400 degrees Fahrenheit. No mold survives that, and no viable spores make it into the bag. On that point the reassurance is complete.

Ochratoxin A is the more interesting question. It is reasonably heat stable, and the research on how much of it roasting removes has been inconsistent for decades. A collaborative study involving nine research groups found reductions in the range of 69 to 96 percent across a range of realistic roasting conditions. Other work has found lower figures under gentler conditions. What no study finds is complete elimination, even at high temperatures.

So the accurate statement is that roasting substantially reduces ochratoxin A without removing all of it. That is still good news. It means a green lot with a modest level arrives in your cup with considerably less, on top of a starting level that was already low.

What the Regulations Say

Ochratoxin A in coffee is not an unregulated frontier. The European Union sets binding maximum levels, and it lowered them in 2023.

A microgram per kilogram is one part per billion. Three micrograms per kilogram is three parts per billion, which is a threshold most roasted coffee sits comfortably beneath.

On the health question, the International Agency for Research on Cancer classifies ochratoxin A in Group 2B, possibly carcinogenic to humans. That classification rests on sufficient evidence in animal studies and inadequate evidence in humans. It is a category that reflects unresolved uncertainty rather than established harm, and it is the reason limits exist and are enforced.

Where Specialty Grading Fits

Specialty grade is a quality standard, and it is worth being precise about what it does and does not measure.

Under the Specialty Coffee Association protocols, a 350 gram sample of green coffee is inspected by hand and a lot must show zero category one defects to qualify. Fungus-damaged beans are a category one defect. A single one disqualifies the lot. The coffee is then roasted and cupped on a 100 point scale, and specialty grade begins at 80 points.

That is a physical and sensory standard, not a laboratory assay. Specialty grading does not test for ochratoxin A, and no roaster should imply that it does. What it does is reject visibly mold-affected beans outright, and the growing, drying, and storage discipline required to produce a clean lot in the first place is the same discipline that keeps mycotoxin levels low. The two are correlated, which is a more defensible claim than pretending one measures the other.

BoneFrog is built on premium organically grown Arabica from Central and South America, selected by Master Roaster Dave Stewart across five decades of sourcing. Careful sourcing is the meaningful control here, well before anything reaches a roaster.

What You Can Control

Almost all of the risk is decided before you own the coffee. The part that is yours is storage.

Frequently Asked Questions