How exciting is dry milling? Not exactly thrilling.
How important is dry milling? Absolutely crucial.
Dry milling is one of the final steps in the value chain at origin and plays a vital role in maintaining the quality of Ethiopia’s finest coffees. Once the parchment passes through grading, it arrives in Addis Ababa, where dry mills receive, store, and schedule it for processing. At first glance, a dry mill may seem like just the place where parchment is removed from coffee beans, but take a closer look, and you’ll see that it’s much more than that.
Hulling
Before hulling, coffee often goes through a de-stoner with a magnet to remove metal or a pre-cleaner to filter out foreign matter.
Next, the hulling process removes the parchment layer along with impurities like stones, wood, and broken beans. Some dry mills also use polishers to remove silver skin, though excessive polishing can generate heat, which may negatively affect quality. Ideally, polishing should be minimal or avoided if the equipment causes overheating.
The coffee then passes through a pneumatic green coffee separator, where a fan blows away any remaining impurities.
Keep in mind that this description is a generalisation of the process, reflecting how most of our partners in Addis Ababa operate. There are, of course, exceptions and variations, especially when it comes to processing washed and natural coffees.
For example, many naturals are initially dry milled (hulled without final grading or sorting) in the interior. These coffees are then transported to a warehouse or mill in Addis Ababa for final grading and sorting before export.
Grading
Once impurities are removed, the next step is sorting the beans by size. This is done using a size grading machine with multiple trays, each containing holes of a specific diameter. The top tray has the largest holes.
As the trays vibrate, the beans move around—smaller beans fall through to the next level, while larger ones remain on top. For reference, beans smaller than size 19 drop to the lower trays, continuing the sorting process. In Ethiopia, beans size 14 and up are generally considered specialty grade.
Density
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.
The lighter beans and shells are separated out as lower grade and are not set out for specialty export. Metal plates at the base of the tray divide the coffee beans so they can be poured into different bags or buckets.
Colour Sorting & Hand Sorting
Another key factor in coffee grading is color. Defective beans often have discoloration or visible defects like insect damage, tipping, or fermentation issues. To remove these, coffee is passed through a color sorter—a machine that uses optical sensors to detect and separate unwanted beans.
While color sorting is highly effective, it comes with trade-offs. If set too strictly, the sorter may remove good beans along with defects, leading to unnecessary losses for producers and exporters. For this reason, many dry mills use a combination of pre-sorting with a color sorter followed by final handpicking. However, not all mills do both.
One challenge with color sorting is that it doesn’t always differentiate between "good" funky beans from anaerobic or natural processing and genuinely defective beans. As a result, some mills only use color sorting for clean, washed coffees while relying on hand sorting for naturals and experimental lots to ensure quality without unnecessary waste.
With hand sorting, trained workers manually remove any beans that don’t meet the buyer’s size, shape, or color standards.
Bagging
With the coffee now sorted and ready, it’s time for bagging and shipping. Specialty coffee is typically packed in 60kg jute bags lined with GrainPro to maintain quality.
Once packaged, the coffee is prepared for export. Dry mills handle the physical filling of containers, while exporters take care of the necessary documentation and final procedures. In some cases, the exporter owns the dry mill, but more often, they use third-party dry mills as a service while still managing the paperwork themselves.
Quality control
To make sure the coffee meets the buyer’s standards, our Ethiopia team and coffee buyers cup and score the final lot in our lab in Addis.
Samples are taken randomly from different bags to ensure they accurately represent the entire lot, not just a single bag. This is known as the pre-shipment sample (PSS)—and we don’t ship any coffee until we or our customers have approved it.
The milling business
In Ethiopia, dry mills are typically owned by private exporters and cooperatives. Some private exporters also offer milling services to other exporters who don’t have their own 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 accommodate dry mill operations must also encompass a big area.
Dry mills are staffed by both permanent and temporary employees.
- Permanent staff includes the dry milling operations manager, inventory manager, loading and unloading coordinators, technical staff, security, and janitors.
- Temporary workers are typically hired seasonally and handle tasks like unloading parchment from trucks to exporters’ warehouses, moving bags within the warehouse, and loading processed coffee into containers.
Temporary workers are usually local groups of friends who are paid based on the number of bags they move. Permanent employees often live in different areas of Addis or on the outskirts, and since public transport is limited, many suppliers provide pick-up and drop-off services for them.
Maintenance
Since coffee is a seasonal crop, dry mills don’t operate year-round. Their final batches—usually late-harvest naturals—are typically milled by the end of August. Once the season wraps up, mills undergo thorough maintenance to prepare for the next cycle.
The expertise of dry mill professionals is crucial to the coffee’s final quality. No matter how good the harvest was, how well the washing stations processed the coffee, or how promising the early cuppings were—if the parchment isn’t milled correctly, there’s no specialty coffee to export.
Why we have a team on the ground
We’ve been operating in Ethiopia since around 2014, and dry milling is a key reason why we have a team on the ground.
In many cases, dry mills and warehouses are the same facility, making stock management a critical part of our work. Our team personally samples stocklots before milling to ensure we know exactly what we’re buying and offering. We carefully mark and track stocklots, ensuring the right bags make it through the milling process. From there, we oversee milling, grading, and pre-shipment sampling to maintain quality and consistency.
A lot can go wrong at this stage—pre-shipment samples may not match type samples, milled coffee might not meet size, shape, or color expectations, and even the loading process presents risks. Containers need to meet quality standards, coffee must be protected properly during shipping, and bags must stay accurately sorted.
That’s why our Ethiopia team is always on-site, keeping a close eye on every step to ensure nothing is left to chance.
This article was originally published in March 2019
