Drawing a green coffee sample in Uganda: increments, sealing and retention

Drawing a green coffee sample in Uganda: increments, sealing and retention

Most Ugandan green coffee changes hands on the strength of a sample. The buyer who never sees the lot buys the sample, and months later, when a container arrives with a different moisture reading or a higher defect count, the same sample becomes the evidence used to settle the argument. That is why the way a sample is drawn, sealed and kept matters as much as the grading result itself.

Grading starts with that sample. The Uganda Coffee Development Authority is explicit that a sample is first obtained to check the size of the bean, the moisture content, the quantity of defects and the foreign matter, and that Ugandan robusta grades must sit at a moisture content of up to 13 to 14 percent, measured with a moisture instrument.

How the sample is built

One handful from the top of one bag tells a buyer nothing about a lot. ISO 4072:1982 is the standard for sampling green coffee in bags, and ISO 6666:2011 covers the triers used to pull coffee out of the bag. A sampler works across the lot and from more than one position, keeping each draw as an increment until enough of them are bulked into a single composite that can speak for the whole consignment.

That composite then has to be turned into a figure both sides can argue about. The out-turn test in the UCDA handbook does exactly this: one kilogram of Kiboko or parchment coffee is weighed on a sample scale, hulled by hand, winnowed, and the clean FAQ weighed. If 540 grams come back from that kilo, the out-turn is 54 percent, and a low out-turn is visible before the lot is ever offered.

The grade itself is only as good as the draw behind it. A screen result, a defect count or a moisture reading taken from a thin or badly placed sample will not survive the first disagreement, which is why the increment record matters as much as the certificate. For how the supply side is shifting, see Teso coffee push: a new Robusta frontier opens in eastern Uganda.

Sealing, identity and retention

A sample without an identity is just a bag of beans. The seal should carry the lot number, the date the sample was drawn, the weight and the moisture reading at sealing. A tamper evident seal, signed across, stops the bag being opened and closed again without anyone noticing. Draw two: one travels to the buyer or the cupping room, one is retained sealed and unopened.

The retained sample is the one that settles a claim weeks later, so it has to be kept as carefully as the coffee it represents. The UCDA handbook warns that re-wetting through leaky tarpaulins, or high humidity inside containers standing for long periods in tropical ports, brings mould and musty flavours into the coffee, and a retained sample stored that way proves nothing.

Both sides should cup the same preparation. ISO 6668:2008 specifies the roasting, the grinding and the beverage preparation used for sensory analysis, so a difference in the cup traces back to the coffee rather than to the kitchen it was brewed in. The same documentary logic runs through other commodities, as in Nigeria's cocoa exports taking a quality-first turn at Lagos.

FAQ

Q: How much green coffee does a sample need?
A: Enough to assess on the screens and to cup, with a retained copy left over. The UCDA out-turn test works from a one kilogram quantity, so a working sample that cannot be weighed and hulled honestly is too small to defend.

Q: Who should seal the sample?
A: Whoever draws it, with the lot number, the date and the moisture reading written on the seal, so the retained copy can be traced back to the lot it came from.

Q: What if the buyer's sample and the retained sample disagree?
A: Check the seals and the lot records first, then cup both under the ISO 6668 preparation, because an unbroken seal on the retained sample is what makes it the reference.

Sources: Uganda Coffee Development Authority | ISO 4072:1982 | ISO 6666:2011 | ISO 6668:2008