Understanding the density of green coffee beans

Esther Gibbs
-
October 20, 2022
Understanding the density of green coffee beans and how it affects coffee roast

When roasting coffee, it is well known the density of the bean is reduced to ensure the coffee is soluble enough to provide the perfect brew. 

For roasters, it is essential they understand the density of their green coffee, as not all beans start with the same density. 

Roasters should take this into account when roasting. Understanding the density of green beans can help them make informed decisions regarding profiling and roasting. More so, it can help roasters eliminate roast defects such as tipping, scorching, or under-roasting.

To learn the density and moisture content of the green coffee they source, roasters can contact their supplier directly. 

Alternatively, they can purchase a moisture and density meter to read it themselves. This can help make roasting easier and is a greater quality control mechanism to have for the business. 

To learn more about how coffee roasters should take green bean density into consideration when roasting, I spoke with David Jameson from Danelaw Roasters

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An image of a coffee farmer on a coffee farm in an article about understanding the density of green coffee beans and how it can affect a roast.

What creates bean density? 

Both altitude and temperature during coffee cultivation may help increase the quality of the bean. 

This is according to Dr. Edgar Morena, a coffee consultant from the Colombian Coffee Growers Federation, who explained the importance of both during an online lecture

Dr. Morean says that due to the nature of the plants, arabica beans tend to be denser than robusta. This is also due to the time it takes for the coffee seeds to grow and develop. 

That said, even within the arabica family, each variety will have a different density. Both the moisture content and growing conditions may impact the density of the bean. 

For instance, if a coffee is grown at a higher altitude and a colder temperature, the plant needs to work harder to thrive. Therefore, it will take longer to grow and produce cherries. This may be one of the many reasons shade-grown coffee is a favoured cultivation method. 

More so, if the environment experiences a sudden and severe temperature drop, the plant will use more energy to “protect” itself. 

Dr. Moreno explains the coffee plant will create a biosynthesis of different metabolites responsible for the high acidity, fruitiness and sweetness often found in high-altitude coffees

These metabolites refer to sugars, proteins, acids, and caffeine within the beans. Dr. Moreno adds that higher altitudes and lower temperatures tend to produce higher-density beans.

In turn, this may affect the acidity and complex compounds within the beans, leading to a better cup. 

Processing methods also have an impact due to water retention and fermentation, which can make the bean denser. 

An image of a coffee roaster roasting coffee in an article about understanding the density of green coffee beans and how it can affect a roast.

What happens to the density of a coffee during roasting?

“Heat transfer is the biggest variable that density affects,” says David, who is also a Q-Arabica Grader and green coffee buyer. “It requires more energy to effectively develop the centre of a high-density bean than a low-density bean.” 

He stresses that this is why it is so important for roasters to understand the density of their green coffee before roasting. 

“If a bean is denser, it requires more energy to penetrate the bean and break down its exterior,” he explains. “In a low-density bean, the cell structure will be more sensitive to heat. This increases the risk of over roasting or baking the beans with too much airflow, or for torching or scorching to occur because the drum is too hot.”

During a roast, the beans lose moisture. During the drying phase, this moisture turns to steam, which becomes the conductor for chemical reactions to occur within the bean. 

Throughout the roast, the chemical structure of the bean is broken down and rebuilt. As the steam pressure builds and the bean reaches the glass density point, first crack happens.

This is where the exterior structure of the bean is broken down to the point where it can no longer contain the pressure, and steam is released. 

Beyond first crack, with the development phase, the heat transfer continues to break down the cell structure of the bean even more, making it more porous and less dense. 

“Darker roasts have the least density, but the largest volume as the bean continues to expand as it heads towards carboxylation and combustion,” David says. “Lighter roasts will have more density but less volume.”

An image of a white multilayer LDPE coffee bag with a chemex  in an article about understanding the density of green coffee beans and how it can affect a roast.

How might you roast a coffee differently because of its density?

If a roaster is struggling with a new coffee, they may benefit from measuring the density of the bean, and adjusting the roast profile. 

David explains that he has a few coffees on opposite ends of the density scale: a natural process Brazil grown at 1,000 miles above sea level, and a high altitude Kenyan from around 1,900 miles above sea level. 

“While there are other differences between the coffees, the approach I take to roasting them is very different,” David says. 

“I found it extremely easy to overdevelop and scorch the Brasil, so roasting it requires a lower charge temperature and a slower application of heat. This allows it to heat through gently, a bit like poaching an egg to leave a runny yolk.”

For the Kenyan, David says he uses as high a charge temperature as possible without scorching. “The aim is for the heat to transfer quickly to the core of the bean. I then reduce the heat application and let the momentum of the roast finish development, which is more like cooking a steak,” he explains. 

An image of a white multilayer LDPE coffee bag on a barsiat bench with roast ground coffee in foreground  in an article about understanding the density of green coffee beans and how it can affect a roast.

Being aware of the density of the coffee allows roasters to make informed decisions when it comes to roasting coffee. Furthermore, it helps them find the ideal profile more quickly, reducing waste and increasing quality. 

Another way roasters can reduce waste and ensure the quality of their coffee is to invest in sustainable packaging. 

We offer roasters and coffee shops a line of 100% recyclable coffee packaging options. Choose from renewable materials such as kraft paper, rice paper, or multilayer LDPE packaging with an environmentally friendly PLA lining, all of which minimise waste.

In addition, we give our clients complete control over the design process by allowing them to build their own coffee bags. Our design team is available to help you customise your coffee bags in order to convey your sustainability efforts to customers. 

Plus, we use innovative digital printing technology, with a quick turnaround time of 40-hours and 24-hour shipping time. 

MTPak Coffee also offers low minimum order quantities (MOQs) to micro-roasters who are looking to remain agile while showcasing brand identity and a commitment to the environment.

For more information on sustainable coffee packaging, contact our team

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