Dry milling, quality depends on it

Dry milling, quality depends on it

March 11, 2019

How exciting is dry milling? Not very. 
How important is dry milling? Crucial.

Dry milling is one of the final steps in the value chain at origin, and is essential for creating and maintaining the quality of Ethiopia’s best coffees. After passing through ECX grading, parchment arrives in Addis Ababa. Dry mills take in parchment, store it and schedule it for processing. At a glance, a dry mill is where the removal of parchment from coffee beans takes place, but look closer and you will discover the dry mill does much more than just this.


Hulling is the first step in dry milling. The parchment is removed, along with impurities like stones, wood, broken beans. Additionally the huller polishes the beans to remove most of the silver skin. Once impurities are separated, the entire mix goes into a pneumatic green coffee separator where these impurities are blown off by a fan. 


After impurities are removed, the next step is sorting beans in the required sizes. The size grading machine has multiple levels, each one with a tray that has holes of a certain size. The top tray has the largest holes. The trays vibrate, bouncing the beans around, and any beans smaller than the holes in the top tray (size 19) will fall to the tray below, and so on. Generally in Ethiopia, anything from size 14 and up is considered specialty grade. In the shipping instructions we give to the miller, we specify size 15 and up.


The next step is to sort the coffee by density. This machine has a single tray set on an angle both horizontally and vertically. The tray vibrates, sending the beans towards the vertical bottom, with the lighter beans remaining at the horizontal top and heavier beans moving towards the horizontal bottom. Metal plates at the base of the tray divide the coffee beans so they can be poured into different bags or buckets.

Colour sorting

Another variance among coffee beans is colour. Beans that are defective often have a different colour, so they are removed by a colour sorter.

Hand sorting

After all these sorting processes, there is still room for imperfections. After all, machines are not as reliable as humans. Thus, colour sorting is followed by hand sorting, a manual process where people remove any beans that don’t match the size, shape and colour requirements of the buyer.


Now we have pure coffee beans, they must be bagged according to the green coffee buyer’s instructions. Gran Pro lined 60kg jute bags are the norm for speciality coffee. Packaging is complete, now the products must be shipped to the desired destination. Dry mills perform the physical filling of containers and prepare necessary documentation and procedures needed for completing a successful export.

Quality control

To ensure the coffee is of the standard requested by the buyer, the final output gets cupped and scored. This is done by taking samples randomly from different bags so the sample is representative of the entire lot, and not just a single bag. This coffee is the pre-shipment sample (PSS) and we don’t ship a coffee until we or our customers have approved this sample.

The milling business

Dry mills in Ethiopia are usually owned by private exporters and cooperatives, but there are government-owned mills leased to exporters and cooperatives that do not possess their own dry mill. The dry mills are usually located on the outskirts of Addis Ababa and are legally required to operate on land large enough for trucks and containers to load, unload and easily move around. The warehouses that can accomodate dry mill operations must also encompass a big area. 

Dry mills are operated by a mix of permanent and temporary employees. The permanent employees include the dry milling operations manager, the inventory manager, loading and unloading coordinators, technical personnel, security personnel and janitors. The temporary employees are usually casual labourers who work only during the season. They unload parchment coming from regional ECX warehouses, they move bags from one area of the warehouse to the other, and they load processed coffee beans to containers. Temporary employees receive payment based on the amount of bags they load, unload or move. Our suppliers pay twice the amount of the usual rate. The temporary employees are usually a group of friends that live in the area around the dry mill and they are paid based on the number of bags they move as a group. The permanent employees live in different areas of Addis or even may be on the outskirts. Either way, most of our suppliers provide pick up and drop off for the permanent employees because public transportation rarely services these outlying areas of Addis Ababa.


Since coffee is a seasonal crop, dry mills do not operate throughout the year. Usually their final coffees, that late harvest naturals, will be milled by the end of August. Once the processing season is over, the dry mills conduct very thorough maintenance. “We can not risk things going sideways during the processing season,” explained one operations manager. These professionals are a crucial part of this value chain and the quality of the coffee often rests on their experience and knowledge. Regardless of how good the harvest was, how beautifully the washing stations processed the coffee, or how great the initial cups tasted, if parchment is not properly milled, there is no speciality coffee to export.

Why we need a team on the ground

Tropiq has been operating in Ethiopia for the past five years and dry milling is one of the main reasons why we have a team on the ground.

There are so many ways things can go wrong at dry mills. Pre-shipment samples might not be consistent with type samples when cupped, processed coffee beans might not end up being the right size, shape, color, weight. In addition to that, loading is an even bigger process that needs sharp attention. Containers might not be of standard, stuffing of containers might not be done well enough to protect the coffee from damage en route, bags might be mixed and end up in other containers. Usually, there is a government appointed inspector, but they can be more a hurdle than a help. Sisay, Tropiq’s lab assistant, is always wary of corruption. “I am quite disliked by loading workers,” she said, because she displays zero flexibility when making sure containers are up to the right standard and stuffing is done properly. 

Sisay’s stubborn behaviour on quality control has been noticed by staff at various dry mills. “You should take it easy a little bit,” one driver said to her, suggesting her extreme stance is taking things too far. Sisay’s response was "this work is serious, and customer satisfaction is everything”.