Dry Milling Green Coffee and Its Significance on Quality

As coffee connoisseurs and enthusiasts, we understand the value of sourcing premium beans, acknowledging the farm's cultivation conditions, and appreciating the initial stages of processing. However, the significance of dry milling green coffee is an often overlooked yet crucial part of the coffee supply chain.  This stage, known as dry milling in green coffee production, significantly influences the final quality of our beans. Let's embark on a journey to explore this less charted territory to better understand its significance on quality.

Understanding Dry Milling in the Coffee Industry

Dry milling is a pivotal stage in the coffee processing chain that takes place after coffee producers have picked and dried their coffee using several unique processing techniques.  At this stage, the parchment coffee (coffee beans still encased in a protective husk) undergoes hulling, grading, and sorting before export.

This process typically takes place in a facility separate from the coffee farm, known as a dry mill. It's an essential step that bridges the gap between the coffee farms and the roasters, ensuring that only the highest quality beans make it through. The dry mill is where the final touches are put on the coffee beans before exporting to coffee roasters all of the world, refining them into the product that will eventually be roasted, ground, and brewed.

Density sorting machines

By understanding the importance of dry milling in the coffee industry, we can better appreciate the journey that each coffee bean takes from the farm to our cup, and the many steps along the way that contribute to the final quality and flavor of our coffee.

Dry Milling's Impact on Our Roasting

As coffee roasters, the quality of our final product significantly depends on the dry milling process.

Green coffee defect chart

 

The Indispensable Role of Dry Milling in the Coffee Supply Chain

Dry milling might seem like a routine, mechanized process, but it's much more than that. It's the last opportunity to ensure only the best beans make it to our roastery.

Removing Defects: The Human Touch and Advanced Technology in Dry Milling

Even with the best harvesting and wet milling practices, defective beans can sometimes make it through to the dry milling stage. These defects can include beans that are too small, cracked, or discolored, among other defects and issues.

One of the most traditional methods for removing these defective beans is manual sorting. In many dry mills, workers stand by a conveyor belt, meticulously inspecting the beans as they pass by. These skilled workers can quickly identify and remove defective beans, ensuring that only the highest quality beans make it to the roasting stage.

Optical sorting machine

However, manual sorting is not the only method used in modern dry mills. Advances in technology have led to the development of automated sorting machines that can quickly and accurately identify and remove defective beans. These machines use a variety of methods, including color sorting technology, which uses cameras and optical sensors to detect discolored or otherwise defective beans.

These technologies, combined with the skilled eye of a human sorter, ensure that only the highest quality, defect-free beans make it to the roasting stage. This rigorous defect removal process is a testament to the importance of dry milling in the production of high-quality coffee.

Another technology used is size grading machines, which separate beans based on their size. This is important because smaller beans can roast faster than larger ones, leading to an uneven roast if not properly sorted.

Density sorting machines

Ensuring Uniformity: The Role of Oliver Gravity Separators in Dry Milling

Uniformity in coffee beans is a critical factor in achieving a consistent and high-quality roast. This uniformity is achieved through grading the beans based on their size and density, a process that takes place during dry milling.

One of the machines commonly used in this process is the Oliver Gravity Separator. This machine separates coffee beans based on their density, a property that is directly related to the quality and flavor potential of the beans.

The Oliver Gravity Separator works by creating a fluidized bed of coffee beans. The denser beans sink to the bottom of this bed, while the less dense beans rise to the top. This separation allows for the removal of less dense, potentially lower-quality beans, ensuring that only the best beans make it to the roasting stage.

The importance of this process cannot be overstated. Beans of different densities roast at different rates. If a batch of coffee includes beans of varying densities, the result can be an uneven roast, with some beans over-roasted and others under-roasted. This inconsistency can lead to a final product with a mix of flavors, detracting from the overall quality of the coffee. By ensuring uniformity in bean density, we can achieve a more consistent roast and, therefore, a more consistent flavor profile.

green coffee screens

The Role of Screen Size in Dry Milling

Screen size is another crucial aspect of the dry milling process.  Evan after all of the above work, the coffee beans are passed over a series of screens with different sized holes. These screens effectively sort the beans based on their size, a process known as screen sizing. Screen sizing is important for several reasons:

green coffee hand sorting

Incorporating screen sizing into the dry milling process is another way we ensure the quality and consistency of our coffee. By paying attention to every detail, from the size and density of the beans to the removal of defects, we can deliver the ultimate coffee experience to our customers.

Dry Milling - The Unsung Hero of Coffee Production

The dry mill might be the unsung hero in the coffee supply chain. It plays a vital role in maintaining quality and consistency in every cup of coffee. As coffee roasters, understanding and recognizing the value of this step ensures we can source the best beans, roast them to perfection, and deliver the ultimate coffee experience to our customers. By shedding light on the importance of dry milling, we hope to elevate the appreciation for this critical stage in coffee production.

Roasting Coffee | The Perfect Coffee Bean

Coffee can seem like a simple thing but there is so much work, knowledge and skill that goes into growing, picking and roasting the perfect bean. As the coffee culture emerges, many are learning and tasting the difference between what really goes into preparing your cup. We interviewed Fratello's Head Roaster, to learn more about roasting coffee, and learn a bit more about the roasting process and how you can pick the coffee that is right for you.

Can you explain the difference between light and dark roast?

The simplest explanation is a dark roast is taken to a higher temperature than a light roast forcing the coffee to go through more chemical changes and darkening the colour of the bean.

What makes for the perfect bean?

Perfection is always strived for and never achieved. The best answer I can give but when looking for high quality beans you are looking at varietal of the bean, soil type, elevation, harvesting methods and processing methods. Typically you are looking for a higher elevation bean because it gives the coffee cherry time to develop properly in a slightly lower temperature than coffee grown at low elevations which get rushed due to the higher temperatures.

IMG_0092

When is the best time to use your coffee beans?

It is dependant what you are using them for, if you are using them for drip coffee, the fresher the better. I would buy enough for a week at a time to ensure you always have great coffee at home. For espresso I would recommend 7-14 days after the roast date for use, this lets the coffee de-gas properly and will pull a much nicer shot under compacted pressure.

Can you walk us through the process of roasting coffee at Fratello?

When coffee comes in to Fratello it has already been sampled at least once to make sure it meets our standards so once it gets in the door it has to be profiled. Each coffee is put through many profile roasts changing the amount of heat used as key times in the roast until we have a roast we are happy with how it performs, some times this can take months of profile roasting and some times it is achieved in the first day. Once we have it profiled it goes into production. A production roast starts by loading the green coffee into the hoppers above the roasters, once the roaster has achieved the temperature desired we release the green beans into the drum of the roaster, it is the job of our roasters to make sure the profile that was decided on during the profiling stage is achieved on a consistent basis, they do this by adjusting the amount of heat depending on how the coffee is reacting that day and making sure the timing on everything is acceptable, coffee roasting is aided by computer software to track the curve but the roaster should always rely on the sight, smell and sounds the coffee is making as it roasts.


When choosing beans for our home use, what should we look for?

Personal preference is huge here, I would recommend going to your local barista and seeing what they suggest based off of what you have previously enjoyed. There is really no wrong answer here some people prefer a very light floral coffee, while others enjoy the heavy bold flavours of a dark coffee. Find something you like and look for other coffee's that are similar. But once again make sure its fresh. Life is to short for stale coffee.