Mycotoxins in Coffee: What They Are, Why They Matter, and How Controlled Fermentation Helps

Coffee safety is not a topic that often surfaces in specialty coffee marketing — which is precisely why it deserves a direct, scientifically grounded discussion.

What Are Mycotoxins?

Mycotoxins are toxic secondary metabolites produced by certain mold species. The two classes most relevant to green coffee are:

Ochratoxin A (OTA): produced by Aspergillus carbonarius and Aspergillus westerdijkiae during the storage of improperly dried green coffee. OTA is a possible human carcinogen (IARC Group 2B) and is nephrotoxic.

Aflatoxins (B1, B2, G1, G2): produced by Aspergillus flavus and Aspergillus parasiticus. Aflatoxin B1 is an IARC Group 1 human carcinogen.

What Do the Regulations Say?

EU Regulation 2023/915 sets the maximum permissible levels for OTA in coffee:

• Roasted coffee: 5 μg/kg (5 ppb)
• Soluble coffee: 10 μg/kg (10 ppb)

OTA contamination is not theoretical — studies of commercial green coffee have found detectable OTA levels in a portion of samples.

How Does Mold Form on Green Coffee?

Green coffee with a moisture content above 12.5% (ICO Resolution 420) provides an environment for the proliferation of Aspergillus species. Moisture management is therefore the primary line of defense against mycotoxin contamination.

How Controlled Fermentation Contributes

Mechanism 1: Competitive Exclusion

LAB produce organic acids that generate pH levels inhibitory to mold growth. Some LAB strains also produce antifungal peptides and hydrogen peroxide. This competitive exclusion effect prevents the conditions that allow OTA-producing molds to proliferate.

Mechanism 2: Closed Bioreactor Environment

Controlled liquid fermentation is carried out in a closed bioreactor system. This prevents external mold spores from environmental Aspergillus sources from reaching the green coffee during fermentation — eliminating environmental contamination.

What Does the Analysis Show?

Analysis of controlled liquid fermented and non-fermented green coffee confirmed:

• Total mold count was reduced in fermented samples
• OTA and aflatoxin levels remained below EU regulatory thresholds
• Shelf-life stability was improved in fermented samples

A Critical Distinction: Prevention, Not Remediation

Controlled liquid fermentation does not degrade or remove OTA that has already formed. This is a preventive control — effective when applied to microbiologically sound green coffee. It is not a remediation strategy for coffee that is already contaminated.

Why It Matters for Specialty Coffee

The specialty coffee market is focused on taste — safety is assumed rather than verified. Integrating mycotoxin risk management into fermentation design simultaneously serves taste quality and food safety.

In this work, batches are processed in such a way as to keep OTA and aflatoxin below EU thresholds. This is a baseline quality standard that should be considered non-negotiable.

Based on: Gercek, Y.C. (2025). "Sensory Quality Enhancement, Mycotoxin Risk Mitigation..." [Zenodo preprint DOI: pending]

Keywords: ochratoxin A, coffee mycotoxins, aflatoxin, coffee safety, lactic acid bacteria, competitive exclusion, EU food regulation, controlled liquid fermented coffee