SUPER DRY: Research highlights hidden moisture risks in coffee shipments

Most people think coffee spoils on the farm. It can also spoil on the ship.

Green coffee is considered safe to export when its bulk moisture sits between 10 and 12 percent. That has been the industry standard for decades, backed by the International Coffee Organization and ISO guidelines.

New research from coffee education platform Change of Tone suggests that number alone is not the full picture.

The average hides the real problem

Coffee is hygroscopic, meaning it constantly absorbs and releases moisture based on its surroundings. On a 4 to 8 week ocean voyage, temperature swings between day and night trigger condensation inside the container, sometimes called “container rain.” That moisture does not spread evenly. It concentrates on the surface of individual beans, creating localised spikes in what scientists call water activity (aW), a measure of how much free moisture is available for biological growth.

The threshold that matters: 0.70 aW. Above that level, mold and yeast can take hold. A shipment can test clean on bulk moisture and still cross that threshold in isolated pockets, wet spots that do not show up on the paperwork.

Why this matters beyond quality

When mold develops, it can produce Ochratoxin A, a mycotoxin that survives roasting even after the mold itself is destroyed by heat. That shifts the conversation from a cupping score issue to a food safety issue.

Two levers exporters can control

The research highlights packaging as one variable: traditional jute bags are breathable but absorb ambient humidity readily, while hermetic and vacuum-sealed options act as a physical barrier against fluctuating conditions.

The other variable is humidity inside the container itself. Calcium chloride desiccants work by actively pulling moisture out of the container air throughout the voyage, reducing the condensation that creates those localised mold-risk pockets in the first place.

Packaging and desiccant protection are not competing solutions. They address different parts of the same exposure.

This article was originally published by SUPER DRY.