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Post-harvest processing · Step 5

Drying

The post-harvest step that lowers the moisture of coffee – as parchment, whole cherry or honey coffee – to a level safe for storage, in the sun, in solar dryers or in mechanical dryers.

Across the chain: Equipment

Source-checkedby Coffearium verification pass· Last source-checked 8 Oct 2026· Prepared with AI assistance· 21 sources (20 tier A)· 4 contested· Updated 8 Oct 2026
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Contents
  • Drying lowers the moisture of processed coffee until it is safe from fungal damage – for parchment coffee, the Codex code of practice considers below 12.5% (wet basis) and a water activity of 0.67–0.70 sufficient.1
  • Coffee is dried in thin layers on patios or raised beds, in solar dryers, or in mechanical dryers that finish the job in one to three days rather than weeks.2
  • The seed is still alive while it dries, and it reacts with germination and drought-stress metabolism.11,12
  • Too much heat damages the seed’s cell membranes; research on Arabica shows damage at 60 °C that is absent at 40 °C.6

Why coffee is dried#

Freshly harvested coffee is wet: a 2026 review gives 50–60% moisture on a wet basis, depending on the processing method and climate.2 Drying brings this down until the coffee can be stored without fungal damage. The Codex code of practice considers a moisture content below 12.5% (wet basis) and a water activity of 0.67–0.70 sufficient to protect parchment coffee.1 Colombian trade rules require parchment coffee to be between 10 and 12%,3 and the 2026 review gives 10–12% (wb) as the safe storage range.2

Drying is also the stage where a lot can go wrong. Rewetting favours rapid fungal growth and the possibility of ochratoxin A production.1 Too much heat damages the seed.4,6

What is being dried#

What surrounds the seed decides how long drying takes.

  • Parchment coffee (washed) has lost its skin, pulp and mucilage before drying. It dries faster than whole cherry.5
  • Whole cherry (natural) is dried with its fruit on. It starts wetter and dries more slowly: in one trial, natural coffee entered the dryer at 2.18 kg of water per kg of dry matter, pulped coffee at 0.87 kg.5 At 40 °C, the natural coffee needed about 88 hours in the dryer and the pulped coffee about 19 hours.5
  • Honey coffee keeps some mucilage. It dries faster than natural coffee but still needs thin layers, frequent turning and good ventilation to prevent clumping and local fermentation.2

The Codex code allows parchment to be heaped and covered after one day of drying, and cherry coffee after three days.1 An FAO manual for Lao PDR gives about 9–10 days of sun-drying for parchment and 18–20 days for cherry.20

The form also sets the temperature the coffee itself can take. A São Paulo state manual limits the temperature of the coffee mass in dryers to 40 °C for pulped cherry (parchment), 45 °C for natural coffee and floaters, and 30 °C for green fruit.19

Drying methods#

Patios. Coffee is spread in thin layers of 2–5 cm on cement, brick or asphalt and turned periodically to improve uniformity and reduce local fermentation.2 The Codex code also lists tarpaulin, plastic canvas, bamboo and sisal mats and raised tables as drying surfaces.1 Patio drying typically takes 7–20 days, depending on climate, and can be interrupted by rain or high humidity.2

Raised beds (African beds). The coffee lies on a mesh on elevated platforms, so air flows both above and below it. The review gives layers of 2–4 cm, turned at least two to three times a day.2

Solar dryers. Greenhouse-type covers (parabolic houses) raise the internal air temperature by about 5–15 °C above ambient. Passive solar dryers cut drying time by about 20–40% compared with open patios, shortening drying from 15–20 days to about 7–12 days under similar conditions.2

Mechanical dryers. Heated air is forced through the coffee. Mechanical dryers finish in about 24–72 hours, depending on batch size, bean moisture and design.2 Static dryers described by Cenicafé use layers of up to 40 cm, and the direction of the air is reversed every 6–12 hours.3 Rotating drum dryers – known in Central America as guardiolas – tumble the coffee in a drum as it dries;18 the review gives residence times of 12–36 hours for drum dryers.2

Combined systems. Many farms pre-dry on patios and finish in a dryer. In the studies of this entry, natural coffee was pre-dried in the sun to about 35% moisture before mechanical drying,4 or pre-dried on a patio for two days (natural) or one day (washed).8 Solar–biomass hybrid dryers cut drying time by 40–60% compared with passive solar dryers.2

051015202530daysMechanical dryer24–72 h2 Solar dryer, passive7–12 days2 Patio, depending onclimate7–20 days2 Sun, parchment (Lao PDR)9–10 days20 Sun, whole cherry(Lao PDR)18–20 days20
Data table
daysSource
Mechanical dryer24–72 h2
Solar dryer, passive7–12 days2
Patio, depending on climate7–20 days2
Sun, parchment (Lao PDR)9–10 days20
Sun, whole cherry (Lao PDR)18–20 days20
Typical drying times by method. Mechanical dryers finish in one to three days; sun-drying takes one to three weeks, and whole cherries take about twice as long as parchment.2,20

Managing the drying coffee#

  1. Thin layers – the Codex code recommends 3–5 cm, which equals 25–35 kg/m².1
  2. Turning – turn the layer constantly during the day to dry faster.1
  3. Protection – wet coffee needs ventilation at night to avoid condensation. After one day (parchment) or three days (cherry) it can be heaped and covered at night or in rain. In rainy regions it must be covered, and spread out again once the surface has dried.1
  4. Keep lots apart – do not mix different types of coffee or coffee from different harvest days.1
  5. Sampling – start taking samples from different points of each lot two or three days before it is expected to be dry.1
  6. Temperature – in dryers, the air temperature should not exceed 50 °C;3 several studies propose lower limits for quality (see Deep dive).4,5 The coffee mass itself should stay at or below 40 °C for parchment and 45 °C for naturals.19

Reference protocol#

The table brings together the parameters reported in the sources for each method. It describes the range found in practice and research, not a single correct recipe. An empty cell means the sources of this entry give no value.

Parameter Patio Raised bed Solar dryer Mechanical dryer
Layer depth 2–5 cm2; 3–5 cm (25–35 kg/m²) on any surface, thicker in dry regions1; 2–3 cm natural, ≤ 2.5 cm parchment19 2–4 cm2 – Up to 40 cm (static dryers); 0.1–0.3 m per layer in three-level dryers3
Turning Constantly during the day1; at least 10 times a day (natural), 20 times (parchment)19 At least 2–3 times a day2 – Air direction reversed every 6–12 h (static/silo)3
Air temperature Ambient Ambient About 5–15 °C above ambient2 Max. 50 °C3; review: max. 50 °C, 40–50 °C best, air or coffee not stated2; 35 °C recommended for specialty naturals4
Coffee (mass) temperature – not air – – – ≤ 40 °C pulped parchment, ≤ 45 °C natural and floaters, ≤ 30 °C green fruit19; above 40 °C causes thermal damage (citing earlier studies)5; one commercial dryer is described as keeping it below 40 °C16; below 40 °C with air up to 80 °C (Cenicafé concurrent-flow dryer)21
Typical time 7–20 days2; 9–10 days parchment, 18–20 days cherry (Lao PDR)20 Faster and more even than patios2 7–12 days (passive)2 24–72 h; 12–36 h drum2
Night and rain Ventilate wet coffee; heap and cover after 1 day (parchment) or 3 days (cherry)1; heap and cover from half-dry to even out drying19 Same rule1 Covered by design –
End point < 12.5% (wb), aw 0.67–0.701; 10–12%3,2 Same Same Same
0102030405060hours to dry from 45% to 12% (wb)Air at 30 °C52 h10 Air at 40 °C34 h10 Air at 50 °C30 h10 Air at 60 °C20 h10
Data table
hours to dry from 45% to 12% (wb)Source
Air at 30 °C52 h10
Air at 40 °C34 h10
Air at 50 °C30 h10
Air at 60 °C20 h10
Drying time of Caturra coffee in laboratory ovens, from 45% to 12% moisture (wet basis). Hotter air dries faster.10

Drying physics#

Drying curves. Cenicafé describes two drying periods: an initial one, in which the resistance to moisture loss lies at the surface of the grain, and a later one, in which it lies inside the grain and the diffusion of moisture sets the rate. For coffee, the second period is the longer one.21 A 2026 study likewise found internal diffusion more important than surface evaporation.10 In thin-layer tests on parchment at 50–70 °C, higher air temperature removed moisture faster and shortened drying.9

Air versus coffee temperature. The limits for the drying air and for the coffee mass are different numbers. Cenicafé caps the air at 50 °C,3 while the São Paulo manual caps the coffee mass at 40 °C (parchment) or 45 °C (natural).19 Evaporation keeps wet coffee cooler than the air: in Cenicafé’s concurrent-flow dryer, where the hottest air meets the wettest grain, the grain stayed below 40 °C while the air reached up to 80 °C.21 As the coffee dries, the drying rate and its cooling effect fall, and the grain temperature rises.21

Effective diffusivity. Because the diffusion period dominates,21 drying is modelled with an effective moisture diffusivity. A 2026 study at 30–60 °C reported values of 10⁻¹³ to 10⁻¹² m²/s and activation energies of about 19 and 28 kJ/mol for moisture diffusion and convective mass transfer.10

Temperature and time. Higher temperature shortens drying: from 45% to 12% (wb), drying took 52, 34, 30 and 20 hours at 30, 40, 50 and 60 °C.10 In a fixed-bed dryer, raising the air from 40 to 45 °C cut drying time by 36% for natural coffee (87.65 to 56.18 h) and 43% for pulped coffee (18.75 to 10.60 h).5

Casehardening. Rapid, uneven moisture removal in mechanical dryers can cause casehardening, in which the outer layers dry faster than the core.2

Rewetting. Sun-dried coffee can lose water quickly at midday and take it back at night or during periods of high humidity.2 Rewetting favours fungal growth and the possibility of ochratoxin A production.1

Uniformity. In static-bed dryers, moisture gradients develop along the airflow path, so the bed has to be stirred or partly unloaded.2 On patios, the São Paulo manual heaps and covers half-dry coffee in the late afternoon to even out drying.19

The living seed during drying#

Germination. Processing switches on germination processes in the seed. Germination activity peaks about two days after the start of wet processing and about one week after the start of dry processing.11

Drought stress. As the seed loses water, its water potential falls and it responds with massive drought-stress reactions.12 Kramer and colleagues followed the stress metabolite GABA (γ-aminobutyric acid) and dehydrin genes during drying. The first GABA peak coincided with germination activity; two later peaks matched maxima of dehydrin expression, thought to be triggered by drought stress in the embryo and then the endosperm.12

Sugars. In washed coffee dried under controlled conditions, glucose and fructose fell significantly within the first day of drying.13 The authors conclude that the lower glucose and fructose contents of washed coffees compared with naturals are, at least in part, due to metabolic processes.13

Membranes. Intact cell membranes are a strong indicator that quality has been preserved after harvest.7 Parchment dried at 40 °C kept intact plasma membranes and oil-body vesicles; at 60 °C the membranes ruptured and oil leaked into the spaces between cells.6 In a microscopy study, damage at 60 °C was already visible when the coffee still held 20% moisture, while sun-dried coffee and coffee dried at 40 °C were undamaged at 11%.7 Natural coffee stays longer in the drying air, which, according to Alves and colleagues, exposes endosperm and embryo to more severe thermal damage.5

Natural versus washed. Natural coffee is more sensitive to heated-air drying than washed coffee and performs worse in physiological tests.5,8 Constant drying at 60 °C was inappropriate for both.8

Rest periods and interrupted drying#

The critical window is the time coffee spends between water activity 0.95 and 0.80, where ochratoxin A-producing fungi can grow; the Codex code cites experimental results showing that 5 days or less in the drying yard prevents ochratoxin A accumulation.1

On farms, drying is often interrupted – at night on patios, or when a dryer is shared. In a Cenicafé trial, washed coffee was dried mechanically for 6 or 12 hours and then held for 12 to 48 hours before drying resumed. Moulds and yeasts were more numerous in the held wet coffee than in the dry parchment, but ochratoxin A showed no treatment effect.17 Taveira and colleagues used a deliberate step instead: air at 60 °C until the coffee reached 30% (wb), then 40 °C, which they found promising for fully washed coffee.8

Risks and defects#

  • Mould and ochratoxin A – rewetting favours rapid fungal growth and the possibility of ochratoxin A production.1 In a 2025 Brazilian study, sun-drying, alone or finished in a rotary dryer, carried higher fungal counts than a mechanical dryer that took about a day, although ochratoxin A stayed below 2.5 µg/kg in all samples.16 Mechanical drying in under 72 hours shortens the window for fungal growth.2
  • Thermal damage – hotter air damages membranes, which shows up as higher electrical conductivity and potassium leaching and lower cup scores.4
  • Too-fast drying – at 35 and 40 °C, a higher drying rate lowered the quality of natural coffee;4 in pulped coffee, a higher drying rate lowered sensory quality.5
  • Uneven drying – casehardening leaves a hard outer shell over a wetter core.2
  • Over-drying – below 9% moisture, coffee risks losing aromatic compounds and becoming excessively dry.16 In multi-level dryers, the outer layers can fall to 6–7% moisture.3 Over-dried coffee is easily damaged in hulling and can taste bland.20

Measuring drying damage#

The Lavras group (Borém, Isquierdo and colleagues) uses physiological tests as early indicators of drying damage: electrical conductivity and potassium leaching of the soaking water, and germination.5,8 Higher sensory scores go with lower electrical conductivity, lower potassium leaching and lower fatty acid values.4

Method and flavour#

Drying method changes chemistry as well as moisture. In Arabica, heat-pump drying at 40–50 °C preserved overall flavour better than tray drying, and sun-dried coffee had less sucrose than heat-pump or tray-dried coffee.14 In robusta, heat-pump drying produced the largest number of volatile compounds, and freeze-drying the highest volatile content.15

Open questions#

  • Temperature limit. Recommendations range from 35 °C (air) to a maximum of 50 °C, with a 60 → 40 °C step also proposed for washed coffee.2,3,4,8 Air and seed temperature are not the same, and not every study reports both.5,16 Mass-temperature limits are set by coffee type in one source19, while another states a general 40 °C damage threshold.5
  • Drying phases. How long the initial, surface-controlled period lasts in coffee is not quantified in the studies cited; Cenicafé describes the diffusion period as the longer one.21
  • Cup effect. Some studies find clear losses with hotter drying,4,8 another finds none between 30 and 60 °C.10

Key studies#

Borém, Marques & Alves, 2008 – Drying damage under the microscope. Parchment Arabica was dried at 40, 50 and 60 °C and its endosperm examined with histochemistry and electron microscopy. At 40 °C the cells were intact; at 60 °C membranes and oil vesicles had ruptured and cell contents leaked.

Biosystems Engineering 99(1), 62–66 · doi:10.1016/j.biosystemseng.2007.09.027

Alves, Borém, Isquierdo et al., 2017 – Temperature, airflow and processing. Natural and pulped coffee were dried in a fixed-bed dryer at 40 and 45 °C with two airflows. Naturals suffered more from heated-air drying; for pulped coffee, 45 °C lowered physiological quality and faster drying lowered cup quality.

Acta Scientiarum. Agronomy 39(2), 225–233 · doi:10.4025/actasciagron.v39i2.31065

Kramer et al., 2010 – Stress metabolism during drying. Tracks GABA accumulation and dehydrin gene expression in drying Arabica seeds. Three GABA peaks appear: one linked to germination, two to drought stress in the embryo and endosperm.

Plant and Cell Physiology 51(4), 546–553 · doi:10.1093/pcp/pcq019

Kulapichitr et al., 2019 – Drying method and aroma. Compares heat-pump drying at 40, 45 and 50 °C, tray drying and sun-drying of Arabica, with sensory analysis and quantification of key odorants. With sun-dried coffee as the reference, heat-pump drying preserved overall flavour better than tray drying.

Food Chemistry 291, 49–58 · doi:10.1016/j.foodchem.2019.03.152

Dong et al., 2017 – Five drying techniques for robusta. Compares room-temperature, solar, heat-pump, hot-air and freeze-drying of robusta. Each method left a different profile of fatty acids, amino acids and volatiles; heat-pump, solar and room-temperature drying grouped together.

Food Chemistry 234, 121–130 · doi:10.1016/j.foodchem.2017.04.156

Contested
  • Air temperature in mechanical dryers: a study on natural coffee recommends 35 °C for specialty coffee and advises against 45 °C4; a study on pulped coffee found lower physiological quality at 45 °C than at 40 °C5; Cenicafé sets 50 °C as the maximum air temperature for parchment3; a 2026 review considers 40–50 °C the range that best preserves quality, without saying whether this is air or coffee temperature2; and a study with a 60 °C start followed by 40 °C found this promising for fully washed coffee.8
  • Coffee (mass) temperature limit: a São Paulo state manual sets the limit by type – 40 °C for pulped cherry (parchment), 45 °C for natural coffee and floaters, 30 °C for green fruit19, while a 2017 study states, citing earlier work, that coffee-mass temperatures above 40 °C cause thermal damage.5 These are limits on the coffee, not on the drying air.
  • Covering at night: the Codex code asks for ventilation of wet coffee at night and allows heaping and covering only after one day (parchment) or three days (cherry)1; an FAO manual for Lao PDR advises covering every night20; and the São Paulo manual heaps and covers from the half-dry stage onwards.19
  • Effect of temperature on the cup: several Brazilian studies found lower sensory quality with hotter or faster drying4,8, while a 2026 oven-drying study found no significant difference in cup score between 30, 40, 50 and 60 °C.10
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Sources

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  15. ADong, W.; Hu, R.; Chu, Z.; Zhao, J.; Tan, L. (2017). Effect of different drying techniques on bioactive components, fatty acid composition, and volatile profile of robusta coffee beans. Food Chemistry 234, 121–130. doi:10.1016/j.foodchem.2017.04.156 · other copies
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Tier A · authoritative · B · trade and expert · C · general. Supporting quotes for every source are in the data version of this entry. If a publisher’s site refuses access, try the doi link or “other copies”.

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