Throughout the entire supply chain, maintaining coffee quality is absolutely essential. One of the most widely used methods is green coffee grading, where coffee beans are analysed based on a number of different criteria before they can be exported.
But once roasters receive their green coffee shipments, it’s important to carry out additional quality checks, too. This process involves measuring several key variables and using the data to adjust roast profiles accordingly. By doing this, roasters can consistently achieve optimal results.
To find out more, I spoke to Linus Peng, founder and CEO of DiFluid, and Dr. Robert McKeon Aloe, an independent coffee scientist and author. Read on for more of their insight on what roasters need to know about analysing green and roasted coffee.
You may also likeour article on how green coffee rehydration can help roasters.
Why roasters need to analyse coffee quality
There are many reasons why roasters would want to analyse their green coffee, but one of the most obvious is to confirm they received the level of quality they paid for.
Linus Peng is the founder and CEO of DiFluid, which designs and manufactures tools and technologies for specialty coffee professionals.
“With the rapid development of the coffee industry, it’s more important than ever to improve quality control,” he tells me.
What’s more, there are a seemingly endless number of factors that influence coffee quality at all levels of the supply chain, including:
- Terroir (or the complete natural environment in which a coffee is grown, including factors such as soil health, topography, and climate)
- Processing methods
- Bean density
- Green coffee moisture content and water activity
- Screen size (or mesh)
To offer excellent coffee, roasters must ensure their green coffee shipments are defect-free and meet their required quality standards. If not, any defects or slight slips in quality will have a huge impact on the final flavour profile – and their customers are likely to notice, too.
Dr. Robert McKeon Aloe is an independent coffee scientist and author of Engineering Better Espresso and Advanced Espresso.
He points out that coffee quality can also change over time, so roasters should monitor different variables over time to maintain consistency.
“Collecting data about green coffee means a roaster can track any changes – from opening the bag to after they have roasted a batch,” he adds.
Which variables do roasters need to measure?
First and foremost, roasters should follow formalised protocol to analyse their green coffee shipments. Many in the specialty coffee industry adhere to procedures established by the Specialty Coffee Association and the Coffee Quality Institute.
To do this, you need at least a 350g sample of green coffee, but more ideally, the sample is representative of the entire shipment of a particular coffee. For instance, if a roaster orders 200 bags of a certain coffee, they should take a sample from 20 different bags.
The practice of green grading is usually performed by a licensed Q grader, who first assesses the colour and smell of the beans, which are then hand-sorted to identify any primary and secondary defects. These can include:
- Broken or chipped beans
- Discoloration (such as black beans)
- Mould or insect damage
Additionally, Q graders will also measure other key variables, as Linus explains.
“During roasting, you need to adjust parameters based on the current water activity, moisture content, bean density, and environmental temperature, and humidity,” he says. “Without knowing these parameters, roasters will often waste a batch of beans in blind roasting experiments.”
Bean size, density & colour
Density is another crucial metric for assessing green coffee quality. Harder and denser beans are generally higher quality – largely because they contain higher levels of sugar, and will therefore taste sweeter.
Similar to density, bean size will also influence how a coffee needs to be roasted to get the best results. For example, denser or larger varieties require a higher charge temperature and a longer development time to ensure an even distribution of heat throughout each individual bean.
This means that per batch, the size and density of beans need to be as consistent as possible. To measure these variables, roasters can use a density tester or simply divide the weight of the sample by its volume. Bean size, meanwhile, is analysed by using a set of screens with specific sized-holes.
When it comes to roasted coffee, understanding how roast profiles impact sensory profiles is key. Agtron spectrophotometers (which use infrared technology) can accurately determine the level of roast profile – with higher numbers indicating a lighter roast. Coffee professionals can then use this technology to adjust roast profiles accordingly to achieve the best tasting results, and allow their customers to experience the full spectrum of a coffee’s flavour.
Moisture content and water activity
“Moisture and water activity play a major role in how you roast and taste coffee,” Robert tells me. “So if there are changes in these variables over the course of several weeks or months, the roaster needs to recalibrate their roast profiles to maintain quality.”
According to the International Coffee Organisation, the ideal moisture content for green coffee is between 8% and 12.5%, which roasters measure using a dedicated tester. Batches with lower levels of moisture typically require less heat during roasting, but a small number of roasters have even started to rehydrate coffee to raise moisture content to more optimal levels.
To comply with food health and safety standards and avoid microbial contamination, water activity must be between 0.4 and 0.6 aw. Roasters can use a water activity meter to obtain accurate and precise measurements.
Linus also points out that temperature and humidity can impact the many chemical reactions that take place during roasting.
“Assessing all these variables not only helps roasters plan their batches ahead, but also indicates how those particular beans should be stored prior to roasting,” he adds.
New approaches to green coffee quality control
Green and roasted coffee quality is the cornerstone of any roastery. But investing in numerous tools and formal qualifications to assess quality, Linus tells me, can quickly become costly.
“Previously, there were only single-purpose professional measuring instruments that weren’t very user-friendly in terms of size, price, and design,” he says.
New technological advancements in coffee quality analysis, however, are helping to meet growing demand for more accurate measurements, greater efficiency, and more comprehensive metrics.
To address this specific demand, Linus explains that DiFluid developed the Omix – an all-in-one tool which can measure and analyse variables like moisture content, water activity, density, and colour in under 30 seconds – that officially launched on 1 June 2024.
“Roasters can simply fill the provided container with the appropriate amount of beans (depending on what is being measured), flatten the sample surface, place the top unit onto the base, and press a button,” he says. “The type of sample (including dried cherry, parchment, and ground coffee) is automatically detected and readings will display on the touch screen.”
Linus explains that the machine can also calculate water activity with precision up to ∓ 0.005 aw, while its scales, infrared imaging, and large-sized sample plate record accurate colour and density measurements – helping roasters achieve uniform and consistent roast profiles.
“The Omix can also give insight into how a specific roast profile changes bean density, moisture, and colour,” he adds.
This is particularly important as collecting data about both green and roasted coffee quality ensures end consumers receive high-quality products.
“Omix is a fast way to collect different data points before and after roasting,” Robert says. “For green coffee, it can give you a better idea of how storage conditions affect the coffee, including whether they are too humid or too dry.”
Using data to improve coffee quality and consistency
To ensure a specific coffee reaches its full flavour potential, roasters must use data to monitor and improve quality over time.
Robert stresses that roasters should consistently collect green grading metrics for every shipment they receive. He says creating standardised protocols for measuring and recording this data can simplify and improve quality control.
“DiFluid’s technology helps quantify and record each step of the process to maximise roasters’ understanding of coffee and obtain their desired results,” Linus tells me.
He adds that the Omix streamlines data collection and storage by automatically sharing information with the DiFluid Café app.
“Users can select multiple historical datasets for classification and summary,” he explains. “The DiFluid Café will automatically visualise the data in graphs, which helps facilitate data tracking and analysis.”
In turn, roasters can easily identify patterns and use information to adjust roast profiles and green coffee storage accordingly, eliminating guesswork and enhancing operational efficiency.
Moreover, better connectivity means roasters can share their data with other coffee professionals around the world – benefiting the industry overall.
Coffee quality will always be a top priority for roasters. To uphold these high standards, accurately measuring and analysing key variables for green coffee is essential.
With ongoing advancements in coffee quality analysis technology, this process is now more accessible than ever before. By carefully measuring certain variables, roasters can continually improve the quality and consistency of their roast profiles.
Enjoyed this? Then readour article on simplifying green coffee grading.
Photo credits: DiFluid
Perfect Daily Grind
Please note:DiFluid is a sponsor of Perfect Daily Grind.
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