Robusta coffee specifications are the measurable limits that define a green coffee lot in an export contract: moisture content, bean size (screen), black and broken beans (B&B), foreign matter (FM) and, in some contracts, a defect count. Each one is tested on a sample drawn from the lot, and each has a typical limit that experienced buyers recognize at a glance.
This guide explains what every parameter measures, how it is tested, the limits you will see on Vietnamese offers, and why each number matters for mold risk, roast consistency and the weight you pay for. It closes with a spec table for Grade 1 screen 18, Grade 1 screen 16 and Grade 2 robusta.
[IMAGE PLACEHOLDER — replace with a real photo, then delete this line] File: robusta-coffee-specifications-moisture-screen-defects.webp · ALT: Moisture meter, screen sieve and defect tray laid out on a grading table at Helena’s Dak Lak mill · Brief: real photo of the lab bench with a 300 g sample
What Are Robusta Coffee Specifications?
Robusta coffee specifications are the physical quality limits written into a spec sheet or contract: moisture (typically 12.5% max), screen retention (for example, 90% minimum above screen 18), black and broken beans (2% max on Grade 1), foreign matter (0.1% to 1% max) and sometimes a defect count per 300 g sample. They describe the green beans, not the roast or the cup.
Species, origin, crop year, processing method, a cup statement and packing usually sit alongside them, but the four physical numbers are what an inspector measures and what a quality claim is argued over. For the labels used in Vietnam (R1, R2, S18, S16), see our guide to the Vietnamese coffee grading system.
Moisture Content: How It Is Measured and Why 12.5% Is the Limit
Moisture is the share of the bean’s mass that is water. Vietnamese robusta contracts almost always cap it at 12.5% max; some Grade 2 contracts allow 13%. The ICO’s Resolution 420 on export quality sets a range of 8% to 12.5% for both species.
How it is tested. Day-to-day checks use electronic moisture meters, which read the electrical properties of a bean sample in seconds. They are fast but drift, so laboratories calibrate them against the oven reference method: ISO 6673:2025 weighs a sample, dries it at 105 °C and reports the loss in mass. The 2025 edition replaced ISO 6673:2003 and is the method used to settle disputes. Meter readings also shift with bean temperature, so let a warm sample cool first.
Why it matters.
- Above roughly 13%, mold can grow during storage and a long sea voyage, bringing the risk of ochratoxin A (OTA), a mycotoxin the EU limits in roasted and soluble coffee (3 and 5 µg/kg, as of October 2026).
- Water is weight. On a 19.2 MT container, every 0.5 percentage point of moisture is about 96 kg of water bought at coffee prices.
- Beans at 12% to 12.5% roast predictably; a lot that swings between 11% and 13.5% from bag to bag will not.
- Too dry is also a fault. Below about 10% to 11%, beans turn pale and brittle, break in handling and lose aroma faster.
Screen Size: Sieves Measured in 64ths of an Inch
Screen size describes bean width. Coffee sieves have round holes measured in 64ths of an inch: screen 18 is 18/64 in (7.14 mm), written as 7.1 mm on the metric sieves used in Vietnam; screen 16 is 16/64 in (6.35 mm, or 6.3 mm); screen 13 is about 5 mm. A line such as “90% min above screen 18” means that at least 90% of the sample by mass stays on the 7.1 mm sieve when it is shaken.
How it is tested. A weighed sample is shaken on a stack of sieves for a set time, by hand or in a mechanical shaker, and the fraction retained on each sieve is weighed and reported as a percentage (ISO 4150 standardizes the method). The 10% that may pass through should be caught by the next screen down, not be dust and fragments.
Why it matters. Uniform bean size means uniform heat transfer in the roaster: fewer scorched small beans and fewer underdeveloped large ones in the same batch. Larger screens also carry a premium because fewer beans in the crop reach them, so a lot that promises S18 and delivers S16 is a money problem as well as a roast problem. Our comparison of robusta coffee screen 18 vs screen 16 covers when that premium is worth paying.
Black and Broken Beans, Foreign Matter and Other Defects
Black and broken (B&B) is the share of the sample, by mass, made up of black beans (fully or partly black, from overripe, fallen, fungus-affected or badly dried cherries) and broken beans (fragments of beans). On Vietnamese Grade 1 robusta the limit is usually 2% max, cleaned lots go far lower, and Grade 2 typically allows 5%. Black beans bring harsh, dirty or fermented flavors; broken beans scorch in the roaster.
Foreign matter (FM) is anything that is not coffee: sticks, husk, stones, soil, string and metal. Typical limits are 0.5% to 1% on standard lots and 0.1% on machine-cleaned lots. Stones and metal are the expensive ones, because they damage grinders and roaster drums.
Other defects include moldy, sour or fermented beans, insect-damaged and immature beans, dried cherries and pods, and quakers (beans that fail to brown in the roast). Our dictionary entry on defects in coffee beans describes each one. Contracts usually cover these with a line such as “free from mold, live insects and foreign odors”.
How they are tested. An inspector spreads a weighed sample, normally 300 g in Vietnamese practice and under the national standard TCVN 4193:2014, picks out each category by hand, weighs it and reports it as a percentage. International guidance counts defects instead: ICO Resolution 420 targets no more than 150 defects per 300 g for robusta (86 for arabica), using equivalence tables in which, for example, several broken beans count as one defect. Know which method your contract uses, because 2% B&B by mass and 150 defects per 300 g are not the same test.
[IMAGE PLACEHOLDER — replace with a real photo, then delete this line] File: robusta-defect-tray-300g-sample-dak-lak.webp · ALT: Black, broken and foreign matter picked out of a 300 g robusta sample on a white grading tray · Brief: real photo, categories separated and labeled
Robusta Coffee Specifications Table: Grade 1 Screen 18, Grade 1 Screen 16 and Grade 2
The table shows the values on our two current cleaned Dak Lak lots and the typical contract values for Grade 2 natural robusta.
| Parameter | Grade 1 screen 18 | Grade 1 screen 16, cleaned | Grade 2 (typical contract) |
|---|---|---|---|
| Screen | 90% min above screen 18 (7.1 mm) | 90% min above screen 16 (6.3 mm) | 90% min above screen 13 (about 5 mm) |
| Black beans | 2% max, black and broken combined | 0.1% max | About 5% max, black and broken combined |
| Broken beans | Included above | 0.3% max | Included above |
| Foreign matter | 0.1% max | 0.1% max | 1% max |
| Moisture | 12.5% max | 12.5% max | 13% max in many contracts |
| Processing | Natural (sun-dried), machine cleaned | Natural, machine cleaned, gravity and color sorted | Natural |
Sources: the product pages for robusta coffee grade 1 screen 18 and robusta coffee screen 16 grade 1; Grade 2 values are typical export terms rather than a specific lot. For how TCVN 4193:2014 defines the grades and how to compare them on cost per usable kilogram, read grade 1 vs grade 2 robusta.
Want these numbers verified on a real lot? Request a 100 g cupping sample of our Grade 1 screen 18 or screen 16 robusta with its certificate of analysis. Our export team replies within 24 hours. Request a Free Sample
How Helena Checks Robusta Coffee Specifications Before a Container Leaves Dak Lak
At our mill in Dak Lak, with a capacity of 100 tons per day, a green lot is cleaned, gravity graded, screened and passed through optical color sorting before it is sampled. We draw samples for the certificate of analysis (COA) and courier a pre-shipment sample (PSS) so you can confirm screen, moisture, B&B and foreign matter on your own bench before the container is stuffed.
On request, SGS, Cotecna, Cafecontrol or Vinacontrol inspect quality and weight at loading; their measured result is also the cleanest basis for any later claim, far stronger than “it tastes a bit woody”. Standard packing is 60 kg jute bags, 320 bags (19.2 MT) per 20 ft container, with kraft paper lining and desiccants; GrainPro liners are available on request. The mill operates under ISO 22000:2018 and HACCP. After arrival, our green coffee storage guide explains how to keep moisture stable until roasting.
Frequently Asked Questions
What is the maximum moisture for robusta coffee export?
Most Vietnamese robusta contracts set 12.5% max, the upper end of the ICO Resolution 420 range of 8% to 12.5%. Some Grade 2 contracts allow 13%, but for a voyage of four to six weeks we recommend writing 12.5% into the contract and checking it at loading with a calibrated meter.
How many defects are allowed in robusta coffee?
It depends on the test. Vietnamese contracts limit black and broken beans by mass, typically 2% for Grade 1 and 5% for Grade 2, plus a separate foreign matter limit. ICO Resolution 420 instead counts defects, targeting no more than 150 per 300 g sample for robusta. Ask which method and sample size apply before you compare offers.
What does “90% above screen 18” mean?
It means at least 90% of the sample by mass is retained on a round-hole sieve of 7.1 mm (18/64 of an inch) when it is shaken. The remaining 10% should be slightly smaller beans that stay on the next screen down, not fragments or dust.
Are robusta coffee specifications the same as cup quality?
No. The physical specifications describe size, moisture and defects, and a lot can meet every number and still cup flat or woody. Cup quality also depends on cherry ripeness, drying and storage, so pair the spec sheet with a cupping sample.
Bottom Line
Four numbers carry most of the weight in robusta coffee specifications: moisture, screen, black and broken, and foreign matter. Know what each measures, which test produces it and what a typical Vietnamese limit looks like, and you can compare any two offers on equal terms. Our next guide shows how to read a robusta spec sheet line by line before ordering.
Need a spec sheet and sample for your next container? Tell us your target screen, B&B and moisture limits, volume and destination port, and we will reply within 24 hours with matching lots, a dated FOB or CIF quote and free samples. Request a Quote or WhatsApp +84 789 818 828.