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Physical Analysis of Green Coffee: What to Measure, Record and Track

Physical Analysis

(Editor’s note: This article written by Andreas Idl and Paul Bartholomew originally appeared in the March/April 2018 issue of Roast magazine.)

Over the past 10 years, our company has had the good fortune to work with some of the best roasters, farmers, consultants, traders and baristas up and down the global coffee supply chain.

Based on this work, we have seen that the best roasters invariably have mastered two distinct skill areas: The first is well established and accepted — how to roast, profile, cup, and perform all the tasks associated with being a production roaster. The second and equally important skill area is green grading/physical analysis. Time and again, we see key customers and an increasing number of our most recognized partners within the specialty industry building expertise and collecting information about their green coffee in greater detail. Why? The same reason they do everything: It has impact on the cup.

“As roasters, our most important limitation is the quality of our ingredient,” says Geoff Watts, co-owner of Intelligentsia Coffee, headquartered in Chicago. “To produce a stunningly delicious coffee requires starting with green coffee that is made to be great by design. No amount of roast sorcery can transform a mediocre-quality green lot into a gorgeous cup. But a lack of understanding of the composition of the green can cause even experienced roasters to perform a perverse kind of alchemy, turning an extraordinary coffee into something unremarkable, by failing to adapt the roast approach to the physical conditions of the coffee. As a roaster, paying detailed attention to the physical qualities of your green coffee is a critical step in learning how to optimize it.“

Identifying Defects

Green grading/physical analysis is an integral part of many industry programs, from the Q grader exam to the World Coffee Roasting Championship, and is detailed in standards developed by the Specialty Coffee Association (SCA), numerous producing countries and other organizations.

There’s a simple reason for this: It’s a critical skill that impacts the final product. Yet, for many years it has been the poor stepchild process in many roasteries. The good news is, green grading appears to be having a Cinderella moment for many players across the industry, and the reasons behind it are worth understanding.

Similar to the rise of roast profiling, roasters who embrace green grading are thought leaders making hypotheses and testing them. The work has created and will continue to create increasing impact across this industry.

Green coffee defects

Green coffee defects can have significant impact on the cup. Pictured: defects from immature cherries.

Our company, Cropster, has always included green grading capabilities in its software packages. After reviewing numerous standards across the commodity and specialty coffee industries, we implemented an adaptable version of the SCA Green Arabica Coffee Classification System (GACCS) that roasters can tailor to their own requirements. We made it expandable to accommodate the numerous standards that exist in green grading across the world, allowing roasters to track qualities and defects specific to their region or interest while keeping the GACCS squarely in the center of these data points.

In the roastery, it’s important to have an adaptable but systematic approach to track qualities roasters are interested in, or add depth beyond the GACCS to a specific element a particular roaster might believe leads to a better cup. Roasters also should be able to determine how often they will check each data point and record it. This is important because GACCS users perform more moisture checks than defect checks, as defects rarely change over time. Having a system that helps tie the GACCS information to everything else roasters know — from origin through packaging, transportation and storage — then review it against sample information and, of course, final cupping results facilitates their ability to put a holistic approach into practice.

The need to adjust one’s roast based on a coffee’s physical properties is well established; the laws of thermodynamics demand it. One will always encounter defects of some kind with an agricultural product. Identifying those defects along with other physical properties as early as possible — and well before the green coffee hits the roasting machine — is key to getting the best from it. As part of the World Coffee Roasting Championship, this skill literally helps define champions.

Beyond Defects

Since its introduction in 2004, the GACCS has effectively established a baseline for identifying moisture content, bean size and defects across the specialty sector. In addition, we have seen some of our key partners move into an increasingly detailed focus on elements such as density and water activity. (While water activity was not included in the original GACCS, the Technical Standards Committee of the Specialty Coffee Association of America added water activity standards for washed arabica green coffee in 2016.)

Defects will continue to exist and need to be tracked, but quality improvements in specialty green have allowed roasters to dig into the details of their physical analysis well beyond categories like black, fungus, sour and insect damage.

“Green coffee is the start of a roaster’s financial commitment to their product, and better information makes for better roasters, better coffee and better business,” says Chris Kornman, coffee quality specialist at Royal Coffee, based in Emeryville, California.

Physical analysis is critical to understanding the value of the raw product and can help provide insight into how the coffee will roast. For example, quantifying water activity can help a roaster make more informed decisions about green coffee on the shelf and, most importantly, how it will react to heat in the drum.

Testing coffee density

Testing coffee density. Photo by Joseph Rivera.

Kornman recently wrote an article for Daily Coffee News titled “The Relationship Between Water Activity and the Maillard Reaction in Roasting.” (As a quick refresher, the Maillard reaction is essentially when amino acids heated in the presence of sugars form a complex mixture of molecules responsible for a range of aromas and flavors. As most roasters know, it is a key part of every roast and has a powerful impact on flavor.) In his article, Kornman describes some of the early research he performed at Royal Coffee and with the Roasters Guild that suggests water activity has significant impact on the preservation of perceived sweetness, acidity and viscosity in the cup. In general, a faster roast can yield higher sweetness and acidity, and a slower roast can yield more balance and viscosity. Kornman highlights that coffees with higher water activity also appear to have a more volatile shelf life. While he acknowledges that his initial results require further research, he is not alone in testing it.

Capturing the data consistently, across many coffees, he says, is a critical step in quantifying the impact of these findings.

“We capture information at every stage of the process using Cropster,” he says. “Logging extended physical information like water activity into a tool that can combine this data with everything from roast profiles to cupping results helps us connect the dots.”

The information required for tracking defects, bean size and other important aspects of green coffee is well established. The same applies to moisture content. Numerous devices that use the capacitance method (essentially measuring changes in the electrical current of a material, such as coffee) make collecting this information quick, easy and inexpensive. These processes are commonly performed in coffee laboratories and roasteries during sample handling. The thing is, until recently, many roasteries stopped measuring these details once the green coffee was in a trusted warehouse with a managed environment or onsite in the roastery. As data people, we find this interesting and confusing. If a metric like moisture content is a critical component of developing a good roast profile, why do people stop measuring it before roasting?

Identifying defects

Identifying defects, which are inevitable with any agricultural product, is key to optimizing a coffee’s flavor through roasting. Photo by Connie Blumhardt.

In his book The Coffee Roaster’s Companion, Scott Rao describes his own experience observing the effects of a dry winter on green coffee, and the work it took him to understand what was happening and apply what he learned to improve his roasting. This highlights the fact that knowing the moisture content of green coffee is key to avoiding many pitfalls, up to and including burning. Rao’s example also points out how seemingly small details like maintaining a consistent environment inside the roastery can have real impact on the cup.

These types of quality variables usually can be mitigated once identified, though identifying the root causes can be time consuming. Collecting information regularly as part of an existing process can save a huge amount of time, reveal a trend before it becomes an issue, and save the cost of lost product or degraded quality.

Capturing information about water activity over a lot’s life cycle establishes a key metric that can affect how roasters should design their profiles. Variances occur across lots, and sometimes even within the same lot. The larger the lot, the greater the chance this will happen. If Rao, 20 years ago, had had the access we have today to tools that easily capture this information, he would have been able to find those variances in the roast much more quickly.

Water activity is another topic where a quick refresher helps (even if you’re a techie at heart). The Handbook of Coffee Post-Harvest Technology, edited by Flávio Meira Borém, does an excellent job of introducing the structures and properties of water and how it interacts with an organic product like coffee. It clearly explains water activity (aw), which is essentially the strength of the bonds between water molecules. In layman’s terms, a glass of water has strong bonds; steam (water vapor) has weak bonds. These differences, while not as extreme, do exist in a coffee bean, and the result is that the amount of heat one needs to apply during roasting varies.

A Practical Approach

This information naturally leads to the question, what data should roasters be tracking? Of course, moisture content, bean size and defects remain essential, but the importance of water activity is growing clearer the more it is studied. At a basic level, that’s because beans with lower water activity lose moisture more quickly, impacting roast duration and temperature. Still, there is a great deal more to be discovered. Water activity also can help indicate how — and explain why — certain coffees introduced to a new environment react so differently. (One aspect of water activity is that it is always trying to reach an equilibrium with its environment.)

Coffee in parchment

After coffee is dried, moisture content and water activity can vary even within the same lot. Monitoring these variables will help roasters determine the best roast schedule and profiles. Photo by Connie Blumhardt.

Recording this information consistently over time will reveal more. We know aging coffee typically gets drier. Regular moisture tracking helps reveal a coffee’s life cycle. Knowing which coffees are losing moisture more quickly in a roastery environment should impact the production schedule. Combined with other information, it could be used to project when a coffee will reach optimal moisture levels (between 10 and 12 percent). It can also reveal inconsistencies across bags. Changing out a bag is often not an option, but adjusting a roast accordingly based on data and experience removes a lot of the guesswork and increases consistency. Also, if a roaster does discover a bad bag, he or she can quantify its issues before it hits the roaster. Establishing a regular protocol to measure and record this type of physical information will make quality claims easier to justify, simplifying what can be one of the most difficult aspects of the business.

Roasteries are dynamic working environments where collecting data has to happen as part of existing critical processes to be effective. This is true across the supply chain. When are the best times to collect and track this information? Whenever a green coffee changes hands, there is a physical check. This is a good start if the data is being collected systematically. We see roasteries where this is happening any time a coffee changes location within the business, and even with regularly scheduled inventory and production planning reviews. Obviously, how long you store the coffee is important. If you roast it within a couple weeks of delivery, you are unlikely to revisit physical analysis. But, if you have a large lot spread over multiple locations, with different delivery dates and changing storage conditions, it’s a good idea to measure and record important physical elements often, as it will reveal a great deal about the effects of time and other variables on the coffee.

Again, using an integrated tracking system will provide the most useful results. Tracking over time will reveal if your confidence in a particular environmentally controlled storage facility is valid, which is difficult to determine when measuring lots in isolation. It also reveals the impact of weather within a facility (even a well-insulated one), and can show the impacts of certain processing methods across a roastery’s production techniques.

New and old roasting machines can collect enormous amounts of real-time information about a roast, but how can roasters capture physical information quickly, accurately, with minimal impact to existing processes and for a reasonable cost? At this point, it is clear the GACCS is the best starting point, with a system in place for recording results. For the price of time and a handbook, any roaster can get started. The handbook — which at press time was set to be rereleased with a new name, The Washed Arabica Green Coffee Defect Guide, in anticipation of the SCA developing similar guidelines for natural-processed coffee — is a classic “boring but important” tool. Get it. Use it. Keep in mind that this repetitive work with green grading is improving your roast, your cup and, importantly, your buying ability. It will help you improve your skills in profiling and cupping, too. This is literally a win-win-win.

Low-density floater defects.

Low-density floater defects.

If you are already on the basic physical analysis bandwagon, the time has come to start capturing density and water activity. Density is quite simple and inexpensive. Many green coffee suppliers already report this information, making it easy to capture and track. If you don’t get density information from your supplier, all you need is a standard size container (typically 250 mL, but any graduated container will do). Simply put the container on a scale, tare the scale, then fill the container with coffee to the 250-mL mark and divide the weight of the coffee by the volume of the container (in this case 250 mL). The number you get is your density. Quick hint: It is much easier to do the math if you use metric measurements.

Water activity is a bit more complicated. You’re effectively trying to deduce the space between water molecules inside your beans. You need a special piece of equipment to do this, such as the Aqualab Pawkit Water Activity Meter. In the past, these machines were cost prohibitive and used only by large, well-resourced companies. Today, an Aqualab Pawkit starts around 2,000 euros (less than $2,500) and fits in a bag. There are also small, portable ones for use in the field. Like color tracking equipment, water activity tools are dropping in both size and price.

Keep in mind that measuring water activity takes time. Sample measurement can take anywhere from a couple of minutes to more than 10, but this is also decreasing with newer models. If you want to start measuring and monitoring water activity, Ian Fretheim wrote an excellent two-part article published in Roast in 2014 titled “Measuring Water Activity in High-End, Specialty Green Coffee.” It’s a great resource for learning more. (Visit to download the article.)

The Roaster’s Responsibility

Why track these physical aspects with such detail if you are working with a green coffee supplier you know and trust? This is another interesting and confusing question for a technical person. In our work with traders and green coffee suppliers, we often find they strongly advocate that their customers perform physical analysis on the coffees they purchase. Quick visits to the websites of numerous importers reveal a trove of useful information on the topics covered here. They are working hard to educate their customers because they see how this education adds value.

Educated customers help suppliers by understanding how to handle the product, what can be expected, and how to properly quantify inconsistencies that can occur. For these high-end suppliers, elements such as bean size and defects are a given, but water activity can and does change, and work in the field suggests these changes have real impact in the cup. Everyone benefits if this information is measured, tracked and shared.

Natural-process coffee

Natural-process coffee drying in Myanmar. Photo by Connie Blumhardt.

This type of tracking and analysis is developing a new understanding of what consistency truly means. Today, we understand that physical consistency runs much deeper than purely external factors such as size, defects, age of the plants and altitude, extending past moisture to the molecular level with density and water activity.

The bottom line is, roasters need to be able to identify the qualities inherent in green coffee, using green grading standards to establish a consistent physical analysis across their businesses and their roasts. This approach will help them increase the quality of their green coffee over time. But more importantly, understanding the nuances of the green coffee they are purchasing will help them become better roasters. Simply put, the more they know about their raw material, the better they will be able to shape it.

Approaching this work with an extensible system for tracking and analyzing the data one collects is the way forward. This method empowers the entire supply chain to mix, match and compare a great deal of detailed information. Roasters can now see trends across supply chains, storage locations, transportation methods, and even locations within their own facility or facilities.

Everything comes down to cupping, flavor and consistency. If roasters encounter defects, they need to recognize what those defects are and try to identify the causes and how to adjust roasting appropriately. This will improve their roasting, their control over key processes like the Maillard reaction and, importantly, their green coffee purchasing and allocation. Tracking this information systematically is another quality process that can yield benefits far beyond improving a single roast.


Andreas Idl is a founder and CEO of Cropster GmbH. As a software developer, he focuses on using his technological experience in socially positive ways. Cropster was created in 2007 to help small farmers in Cali, Colombia; today it is the specialty coffee industry’s leading software platform.

Paul Bartholomew is head of marketing at Cropster. He has been helping businesses benefit from advances in technology for more than 30 years.


1 Comment


Hi there,
Great article! How does the physical analysis as portrayed in the article can be matched with technical standards from origin countries? I mean, does that actually matter, or Cropster develops its own system regardless of technical standards from each supplying country.


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