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  • Writer's pictureJon Ferguson

From Parchment To Green: The Dry Milling Process

As we begin the new harvest season in Peru, the Café Selva Norte dry mill prepares to process their first full harvest season for cooperatives and clients near Jaen, Peru. As of September 2021, the Cimbria-equipped dry mill has provided a much-needed resource to the cooperatives and coffee organizations across Cajamarca and Amazonas.

For a further look into how coffee is processed and prepared for exportation at the Café Selva Norte dry mill, ElevaFinca reached out for an interview with Stefan Lautner, the Cimbria Sales Manager in South America. Stefan has worked for nearly a decade with Cimbria, now residing in Lima. He has played an integral role in drafting documentation and overall planning, installation, and technical support for Cimbria machinery installed at the Café Selva Norte dry mill.

During our interview with Stefan, we discussed the steps involved for processing coffee, along with the machinery and technology used for accomplishing each activity. The following provides an overview of the flow of coffee from the time it is received at the mill to the time that coffee is loaded onto a container for exportation.

Stefan Lautner (Sales Manager at Cimbria), Jon Ferguson & Erly Camizan (from ElevaFinca) at the SCA Expo in Boston.

Arriving at the Mill

Prior to parchment arriving at the dry mill, most of the coffees have received several layers of quality control analysis including moisture content, physical grading, screen size, and cup quality. Once the cooperative or client has finalized specifications for each coffee delivery, the machinery is calibrated to achieve the highest output of their desired quality specifications.

Stage 1: Cleaning

As the coffee enters the facility, the top screen of the pre-cleaner removes the dust, debris, and dry cherries. The bottom screen removes broken beans, smaller stones, and sand.

Stage 2: Destoner

After the cleaning of the parchment, the coffee passes through a destoner, removing larger rocks, pieces of concrete, and all foreign matter which has a higher density than the coffee being processed.

Stage 3. Huller

Coffee parchment is much like the shells still attached to a peanut. The huller removes the outer brittle parchment shell from the coffee seed (i.e., bean). Once the parchment is removed, the coffee is polished to remove a layer of silver skin that lightly blankets the bean. In washed Peruvian coffees, processors and buyers typically request highly polished coffee with no silver skin attached.

Stage 4. Screen Size

After polishing, the coffee passes through several layers of screens to sort the coffee by bean size. The main goal for sorting by seed size at this stage is to prepare the coffee for sorting by density. If coffee is not screened and sorted by size prior to density sorting, there would be a greater loss of product, as density separation uses air pressure and turbulence to sort similar-sized beans into different levels of density. With a uniform size on each gravity table, the process will be much more precise and efficient.

Stage 5. Density Separation (Gravity Table)

The coffee is divided into two different sizes for the grading tables. The variety of the coffee also determines how the density separation is calibrated and sorted. Normally, 14 to 17 screen-sized beans are run on the same gravity sorting table, while coffees screened between 17 to 19 sizes are on another table. The owner of the coffee can adjust these parameters as desired.

Having two tables creates the ability for running a continuous process, using two different sizes on two different gravity table sizes at the same time. Every gravity table will produce higher density coffee, along with a smaller percentage that will be re-processed to reduce waste.

Stage 6. Color Sorting

Full-color cameras located in the machine provide optical sorting, which is extremely helpful for identifying certain defects which otherwise will pass through the density, sizing, and cleaning stages. For example, color sorting removes full blacks, yellowish defects, and can even identify slight insect damage, where the small hole formed from insects on the seed didn’t impact the density of the seed. With optical color sorting, the optical sorter can identify extremely small black dots or shadows created by slight insect damage.

Café Selva Norte dry mill is the only company in Jaen that operates with the Chromex color sorting technology, using full color and high-resolution optical sorting processing.

Stage 7. Weight and Fill

The final processing stage consists of filling bags ready for exportation. At the end of the line, there are fresh stacks of properly printed burlap sacks, along with bag liners (i.e., Ecotact, GrainPro) which create a hermetically sealed environment for each 70kilo bag.

Workers open each burlap sack, add a bag liner, and place the burlap and liner on top of a floor scale positioned under a large coffee bin to begin the filling process. Once the portioning is complete, the bag is sewn shut, stacked onto a pallet, and transferred to a warehouse location for container fulfillment.

Equipment Calibrations and Adjustments

With Cimbria processing equipment, the operators do not need a lot of time to switch to new contract specifications and requirements. Basic adjustments include;

  • Screens for sorting can be easily changed.

  • Adjustments for gravity tables are accomplished during operations.

  • Color and defect identifications can be saved on the color sorter memory. Adjustments can be accomplished by selecting defects and colors via computer.

Café Selva Norte Capacity

Currently, the capacity of the dry mill has two processing lines. The main processing line processes five tons of parchment per hour. The line is positioned to increase capacity to 10 tons per hour. This will be accomplished by adding a second hulling machine. At this moment, the Cimbra team and Café Selva Norte are working with the local team to establish the additional necessary equipment.

Micro-lot Capacity

If a client would like to process smaller batches through the mill, they will have the opportunity to do as little as three full bags (250 kilos) at a time. The operator must control the machines manually in a start/stop mode, but operators have control over the machines as they are smaller and more manageable than alternative processing lines.

What is different about Cimbria equipped mill?

When Cimbra designs a plant for processing, they design with sustainability in mind. These factors include the following;

Product Quality

Cimbra does not change the characteristics of the bean. The machinery uses precise separation, with minimal damaging, resulting in very low product waste.

Worker Safety

Cimbria creates a 0% dust work environment. There is a thoughtful design to create healthy air, with easy and safe equipment operations.


There is low pollution with high dust separation throughout the process. The parchment is recycled and used for making bricks to help heat furnaces for coffee dryers.


Cimbria equipment designs facilities to create very low energy consumption. There are very low maintenance costs. For example, the screen machine and destoner are designed to be maintenance-free for a lifetime. In general, belts are needed for regular maintenance, but these are easy to source locally.

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