Green Bean Standards for Fine Robusta: Defects, Moisture, Size & Uniformity

Introduction to Green Bean Analysis

Before a Robusta lot can even be cupped, it must pass a rigorous physical inspection. The CQI's green-bean standards are designed to ensure that only clean, well-prepared coffees reach the sensory evaluation stage. This inspection focuses on four key parameters: primary defects, secondary defects, moisture content, bean size, and uniformity. Each parameter has clearly defined tolerances, and exceeding them automatically disqualifies a lot from being classified as Fine Robusta.

Primary Defects – The Deal-Breakers

Primary defects are the most severe physical flaws that can ruin a cup. They include:

Full Black Beans – over-fermented or heavily infected beans that impart foul, tarry flavours.

Full Sours – beans that have undergone uncontrolled fermentation, resulting in sour, vinegary notes.

Fungus-Damaged Beans – contaminated with mould, which produces mycotoxins and off-tastes.

Insect-Damaged Beans – pierced by pests, often leading to enzymatic browning and rancidity.

According to CQI protocols, a 300-gram sample of green Robusta must contain zero primary defects to qualify for Fine Robusta status. Even a single primary defect is grounds for rejection.

Secondary Defects – Tolerances and Impact

Secondary defects are less severe but still affect cup quality. They include:

Partial Blacks and Partial Sours – beans that are only partly affected.

Parchment – dried husk fragments that add a woody taste.

Broken / Chipped Beans – physical damage that can cause uneven roasting.

Floaters – under-ripe, lightweight beans that result in baked or grassy flavours.

The CQI allows a maximum of five secondary defects per 300-gram sample for Fine Robusta. Any more than that, and the lot fails the physical inspection, regardless of its cupping score.

Moisture Content – The Critical Range

Moisture content is vital for bean stability, flavour development, and shelf life. The CQI specifies that Fine Robusta must have a moisture content between 10% and 12.5% (on a wet-basis).

Below 10%: beans become brittle, lose essential volatile compounds, and taste flat.

Above 12.5%: risk of mould growth, fermentation, and rapid quality deterioration during storage.

Producers should use calibrated moisture metres and sample consistently from different parts of the lot to ensure representativeness.

Bean Size and Uniformity

Robusta beans are typically larger and rounder than Arabica, but uniformity still matters. The CQI requires that at least 90% of the beans fall within two adjacent screen sizes (e.g., 16/17 or 17/18) for a given lot. This ensures even roasting and consistent extraction.

Under-sized beans (peaberries or smalls) roast faster and can scorch;

Over-sized beans may roast unevenly, leading to a mix of under- and over-developed flavours.

A sieving test using standard perforated plates is mandatory. Lots with excessive variation are downgraded or rejected, as they compromise the roaster's ability to produce a balanced cup.

Practical Tips for Producers and Buyers

For producers: Invest in proper hand-sorting tables, density separators, and moisture control during drying. Regularly test your samples against CQI standards to catch issues early.

For buyers: Insist on sample-size inspections before committing to a purchase. Use a graded sieve and a moisture meter as your primary tools. Remember – physical quality is the foundation of sensory excellence.