Trilla Explained: From Pergamino to Export-Ready Green Coffee

Follow a Colombian coffee farm tour to its logical end and you run into a gap. The tour shows you picking, the wet mill, the drying floor — and then the coffee appears roasted in the tasting room, with a step quietly skipped in between.

That step is trilla: dry milling. It is where parchment becomes green coffee, where the grades that appear on export documents are decided, and where a meaningful share of remaining defects is removed. Most farms do not do it themselves, which is exactly why it gets left out.

What trilla actually is

Coffee leaves the drying floor as café pergamino seco — dry parchment. The seed is stable, but it is still wrapped in a brittle beige husk, and inside that, clinging to the crease, there is usually a thin remnant of silverskin.

Trilla removes the husk and delivers café almendra, or green coffee: the dense blue-green seed that gets bagged, shipped and eventually roasted. Everything after hulling is sorting, and sorting is most of what a dry mill is for.

The distinction between the two mills is worth fixing in your head:

Stage	Facility	Input	Output
Beneficio húmedo	On the farm	Fresh cherry	Wet parchment
Secado	On the farm	Wet parchment	Dry parchment
Trilla	Off the farm, usually	Dry parchment	Green coffee

The huller

The machine itself is unglamorous — typically a screw or friction huller that cracks and strips the parchment off without breaking the seed inside. Set too aggressively it chips and fractures beans, which is why over-dried coffee is a problem here: brittle beans shatter, and broken beans are a defect that gets sorted out and discounted.

The husk that comes off is called cisco, and it is not waste. It burns well and is widely used as fuel for mechanical dryers and roasters, which closes a small loop rather neatly. The rest goes to mulch and compost.

Coffee loses a substantial share of its weight at this point — the husk is a real proportion of what went in. That loss is the basis of the number the whole Colombian trade runs on.

Rendimiento: the number that sets the price

When a Colombian grower sells dry parchment, the price is not a flat rate per kilo. It is adjusted by a yield factor — the factor de rendimiento — which measures how much parchment is required to produce a fixed quantity of export-grade green coffee.

The convention is expressed as the kilograms of dry parchment needed to yield 70 kilograms of excelso, and the reference standard sits at around 94. A farm whose coffee mills out better than that — well-filled beans, low defect count, correct moisture — needs fewer kilos to hit the target, gets a better factor, and is paid a premium. A farm delivering poorly filled or defective coffee needs more, and is discounted.

The other unit you will hear constantly is the carga: 125 kilograms of dry parchment, the standard Colombian trading lot. National reference prices are quoted per carga, and it is the number growers talk about among themselves.

Sorting, in four passes

Hulled coffee is not yet sellable. A dry mill puts it through a sequence of separations, each catching something the previous one missed.

Density

Green coffee is run over a gravity table — a vibrating, tilted, air-fed deck that stratifies beans by weight. Dense beans, which are generally the well-developed high-grown ones, migrate one way; light beans, insect-damaged beans and hollow ones migrate the other. Density correlates strongly with quality, so this pass does a lot of work.

Screen size

The coffee then passes over stacked perforated screens with progressively smaller round holes. Screen sizes are given in sixty-fourths of an inch, which is why the numbers look arbitrary — a screen 17 bean passes a 17/64 inch hole but not a 16/64 one.

Size sorting is not primarily about quality. It is about roasting: a batch of uniformly sized beans roasts evenly, while a mixed batch will scorch the small ones before the large ones are developed.

One category gets separated here for a different reason. Occasionally a cherry produces a single rounded seed instead of two flat-faced ones. Colombians call it caracolillo; English-speaking trade calls it peaberry. It is pulled out because its shape rolls and roasts differently, and it is often sold at a premium on the strength of a widely held belief that it tastes better — a belief that is genuinely contested among roasters.

Colour

Optical sorters run the coffee past cameras and eject anything outside the target colour range with a puff of compressed air. This catches the defects that density and size miss: black beans, sour fermented beans, insect-bored beans, foreign material.

The machines are fast and very good, and they are also expensive, which is one of several reasons small farms do not own them.

Hand

At the top end, coffee still gets sorted by hand on a moving belt, usually by women who have done the job for years and can spot a defect in a moving stream faster than a visitor can find it in a still one. It is slow and it is not economical for commodity lots, but for a high-value microlot it is standard.

Excelso, Supremo, and what the grades mean

This is where most visitors have absorbed something slightly wrong, usually from a bag of supermarket coffee.

Excelso is the general export classification for Colombian green coffee — the broad quality standard the country ships under. Supremo is a subdivision of it based on the largest screen sizes.

Which means the widely repeated idea that Supremo is Colombia's top grade is a size statement dressed up as a quality statement. A large bean is not a better bean. It roasts more predictably in a batch of other large beans, and it looks impressive, and the market has historically paid for it — but plenty of exceptional Colombian coffee grades out below Supremo on screen size alone.

The specialty sector has largely moved past the whole system. A single-farm microlot is sold on its variety, its process, its altitude, its producer and its cup score, and the size grade barely comes up. If you buy coffee at a farm gate in Colombia, the label will tell you the things that matter and probably will not mention Supremo at all.

Why farms rarely mill their own

A hulling machine, a gravity table, a screen stack and an optical sorter represent a capital investment that makes no sense against a couple of hectares of coffee. The volume is not there.

So the normal path for a Colombian smallholder is to deliver dry parchment to a cooperative or purchasing point, have it weighed and graded on the spot, and get paid against the day's reference price adjusted for the yield factor. The milling, sorting and export happen further down the chain.

The exception is the farm that has gone direct — selling its own roasted coffee at the gate, running its own brand, exporting microlots to named buyers. Those operations sometimes own a small huller, or more often contract milling in small batches so their lots stay separate. Farms you can tour skew heavily toward this group, because a farm with a tasting room and a shop has already made the decision to sell its own coffee rather than deliver it into the commodity stream.

Seeing it for yourself

Trilla is not on the standard tour, and asking for it specifically is the way to get it. A few options that do exist:

• Cooperative purchasing points in coffee towns, where you can watch growers deliver parchment and see it weighed and factor-graded. Public, busy, and completely unstaged.
• Full-day specialty tours that follow a lot beyond the farm gate rather than stopping at the tasting room.
• Farms that mill and roast their own — smaller equipment, but the full sequence under one roof and someone who can explain every step of it.

It is the least photogenic stage in the chain and the one that explains the most about how the money actually moves. If you have already seen the picking, the wet mill and the drying floor, this is the piece that connects them to the price on the bag.