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Drying lowers seed moisture so coffee can be stored and shipped. Washed, natural, and honey processes all require drying, with different tissues remaining around the seed. Raised beds allow airflow above and below the coffee, while patios use a solid surface. Drying rate and uniformity can affect storage and sensory quality.
Washed, natural, and honey processes all require drying to lower seed moisture for storage and shipping. Although bags may not describe this stage separately, it affects the coffee’s subsequent quality.
TechnoServe’s wet-mill guide describes solar or mechanical drying that lowers washed parchment coffee from about 57% moisture to about 10 to 12% on a wet basis. That range is the handbook’s operating reference and may differ from requirements elsewhere.
The Codex code of practice for preventing ochratoxin A contamination specifies a maximum moisture content of 12.5% after drying to reduce the risk of mold growth and toxin production. ICO Resolution 420 from 2004 specifies moisture between 8 and 12.5%, measured using ISO 6673, for export coffee labeled S.
Drying uniformity at origin affects how long coffee keeps, the risk of mold during storage, and breakage when the parchment is removed.
Parchment coffee can be spread on concrete patios, tarpaulins, or raised beds for sun drying. TechnoServe describes most East African coffee as drying on raised beds, with mechanical dryers more frequent on large estates. Codex also lists cement or brick terraces, tarpaulins, mats, and raised mesh tables, and describes combining solar and mechanical drying in stages.
Raised mesh beds allow air to circulate above and below the coffee. A 2026 drying review associates them with less contact with soil, dust, and animals, and fewer poorly ventilated areas that remain anaerobic. Patios use a solid surface with airflow mainly above the coffee, offering greater capacity and lower construction costs. Appropriate layer depth and turning in a stable, dry climate can also bring patio-dried coffee to a moisture level suitable for storage.
Washed coffee is typically cleaned to parchment before drying; natural coffee retains the whole fruit, while honey coffee retains mucilage after pulping. With more fruit and sugar around the seed, drying is more likely to overlap with fermentation. Wet-hulled coffee has its parchment removed before reaching the moisture levels common for export, then continues drying with the seed exposed.
Mechanical drying is less affected by rain and offers greater control over processing conditions, though the review also notes higher energy use. TechnoServe warns that overly rapid drying can harm quality and recommends bean temperatures under 40°C, with actual conditions varying by dryer.
Drying requires a controlled, even reduction in moisture. TechnoServe describes removing surface water first, followed by a slower, steady reduction toward 10 to 12%. Excessive speed may prevent moisture from leaving the seed’s center evenly, affecting color and quality. Insufficient or uneven drying leaves wetter beans vulnerable to mold in storage, which also poses a health risk. Rain and nighttime moisture can interrupt the process.
The University of Hawaiʻi publication describes increased risk of quality loss from bacteria, mold, or yeast above about 12% moisture, and possible shrinkage and distortion below about 9%. TechnoServe describes declining aroma, acidity, and freshness below 10%, along with greater breakage during hulling and effects on appearance and weight.
Washed, natural, and honey coffee all require drying to a moisture level suitable for storage. They differ in whether the seed retains fruit skin and mucilage or has been washed to parchment before drying.
Raised beds allow airflow above and below the coffee and reduce contact with soil and animals, but patios can also dry coffee well in a dry climate with careful turning. Flavor depends on the lot, other processing conditions, and roasting, rather than the equipment alone.
The time required varies with weather, layer depth, airflow, and mechanical assistance, so no fixed duration applies to every mill.
Fermentation involves microbial breakdown of mucilage, while drying lowers seed moisture for storage. The two can overlap during natural processing, as explained in the fermentation article.
TechnoServe describes loss of aroma, acidity, and freshness below 10% moisture, along with greater breakage during hulling. The Codex maximum of 12.5% addresses a different concern, reducing the risk of mold growth and ochratoxin A associated with excess moisture.