Drying and the Dry Mill

Why Drying Matters

After processing, coffee exists as parchment -- the bean wrapped in a thin papery hull. At this stage, moisture content is typically 45-55%. The goal of drying is to bring it down to 10-12% for safe storage without damaging the cellular structure that holds flavor compounds.

Dry too fast and the outer layers harden while the interior stays wet, creating conditions for mold. Dry too slowly and uncontrolled fermentation produces off-flavors. On our farms in Caicedonia, Valle del Cauca, we monitor moisture at every stage using calibrated moisture meters. There is no guessing here -- a single percentage point can mean the difference between a lot that stores well for months and one that degrades within weeks.

Drying Methods

We use two primary drying approaches across our farms:

Raised Beds (Camas Africanas)

Raised beds allow air to circulate above and below the parchment. This is the gold standard for specialty coffee drying.

• Layer thickness -- coffee is spread 2-4cm deep
• Turning frequency -- every 30-45 minutes during the first 2 days, then every 2-3 hours
• Duration -- typically 10-18 days depending on weather and process method
• Advantage -- even drying, excellent air circulation, reduced mold risk

I always tell our team: the beds are where patience pays off. Rushing this stage -- piling too thick, turning too rarely -- is one of the fastest ways to ruin a lot that was perfectly processed.

Mechanical Dryers (Silos)

When rain threatens or volume exceeds bed capacity, mechanical dryers provide a controlled alternative.

• Temperature -- never above 40-45 degrees Celsius to protect flavor compounds
• Airflow -- continuous, gentle forced air
• Duration -- 24-48 hours to finish drying
• Common practice -- pre-dry on beds for 2-3 days, then finish in the silo

During one particularly rainy harvest in Caicedonia, we had no choice but to move nearly all our honey-processed lots into the silos. The key was keeping temperature below 42 degrees. Above that, you start losing volatile aromatics -- the floral and fruit notes that make specialty coffee special. We managed it, but it was tense.

The Critical Moisture Window

Moisture content determines everything about storage stability and export readiness:

• Above 12% -- risk of mold, fermentation, and rapid quality degradation
• 10-12% -- safe zone for storage (up to 6 months in proper conditions)
• Below 10% -- the bean becomes brittle, loses flavor compounds, and can develop "baggy" or woody flavors
• Export standard -- most buyers require 10.5-11.5% moisture on arrival

We track humidity readings for every lot to ensure compliance before any coffee leaves our warehouse.

The Dry Mill: From Parchment to Green

Once parchment coffee is properly dried and rested (ideally 30-60 days in reposo), it moves to the trilladora (dry mill) for final preparation:

1. Hulling (trilla) -- mechanical removal of the parchment layer to reveal the green bean

2. Density sorting -- vibrating tables or air columns separate beans by weight, removing lights (underdeveloped beans)

3. Screen sizing -- beans are separated by physical size through calibrated screens

4. Color sorting -- optical machines or hand sorting removes defective beans (blacks, sours, broken)

5. Grading -- the final lot is assigned a screen size, defect count, and preparation grade

Each lot at our dry mill carries full traceability: farm, plot, variety, process method, harvest date, and SCA score. This level of detail is what allows us to offer buyers transparency from seed to shipment.

Pretrilla Analysis

Before hulling, we perform a pretrilla analysis -- cracking open a sample of parchment to inspect the green bean inside. This reveals defects like broca damage, immature beans, and physical deformities that are invisible through the parchment layer. It is our last quality gate before committing a lot to the milling process.

I review every pretrilla report personally. If broca damage exceeds our threshold, that lot gets separated before it ever reaches the grading stage. It is better to catch a problem here than to discover it in a buyer's cupping lab halfway around the world.

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This post is part of our Seed to Cup series. Want to see real pretrilla analysis data from our lots? Join our free community at skool.com/particular-3064 for behind-the-scenes content from the dry mill and warehouse.