August 10, 2021

A guide to roasting robusta coffee

Arabica makes up some 60% of all coffee consumed around the other world. After that, canephora comprises almost all of the remaining 40%, as both robusta and conilon coffee. 

But while there is plenty of information about how coffee professionals around the world roast arabica coffee, how do you do things differently for robusta?

To learn more, I spoke to two robusta experts. Read on to find out what they told me, and some tips for anyone looking to roast fine robusta coffee.

You might also like our article exploring the link between canephora and robusta.

unroasted robusta coffee beans

Robusta vs arabica: An overview

There are several key differences between robusta and arabica as coffee species. While arabica can be traced back to Ethiopia, robusta is believed to be native to West Africa. 

While arabica is generally grown above 1,000 m.a.s.l., robusta thrives at much lower altitudes. It can also withstand much higher temperatures, growing best between 24°C and 30°C. Robusta’s yield is also generally much higher.

Arabica is also susceptible to fungal diseases like coffee leaf rust, as well as pests like the coffee berry borer. 

Robusta beans contain significantly more caffeine than arabica beans – around twice as much, in fact. The concentrated caffeine acts as a natural pesticide, repelling coffee berry borers and other harmful bugs.

It is also naturally more resistant to coffee leaf rust, and all-round a stronger and hardier plant.

Finally, the structure of the bean itself is also different. Robusta beans are generally smaller and rounder in shape, and because of the lower altitude and higher temperature they are grown at, they also have a lower density.

Cleia Junqueira is a roastmaster at Coffee Planet in Dubai. She is also a Q robusta grader (also known as an R grader). She tells me about the optimal growing conditions for the robusta plant.

She says: “Ideal average temperatures range between 24 to 30ºC for robusta, which can flourish in hotter, harsher conditions and can be grown between sea level and about 800 m.a.s.l.

“The term ‘robusta’ is actually the name of a widely grown accession of this species and is grown in West and Central Africa, throughout Southeast Asia, and to some extent in Brazil, where it is locally known as conilon.”

coffea robusta plants

Genetic diversity and adaptation

Robusta plants are also highly adaptable and able to thrive in a wide variety of habitats. This is largely thanks to the species’ incredible genetic diversity, and to a lesser extent, the fact that it has a simpler root structure than arabica.

Lucas Venturim is owner of Fazenda Venturim, a coffee farm in Brazil that produces high-quality robusta – known among the wider coffee community as “fine robusta”. He tells me more about the species.

“Canephora coffees (robusta or conilon) have a great capacity for adaptation, mainly due to their outstanding genetic diversity,” he says.

“These plants are cross-pollinated, and this provides an almost infinite genetic matrix, which allows good adaptation to very varied climates, from dry and hot to humid and milder temperatures.”

The complex genetic diversity of the robusta species comes down to the fact that it cannot self-pollinate. It is largely dependent on cross-pollination, ensuring that plants receive genes from both their “mother” and “father”.

In fact, many farmers choose to plant several robusta varieties in the same area, promoting cross-pollination and maximising genetic diversity.

“In our region, a genetic selection was made to adapt to our climate. It’s very sunny with concentrated rains in the summer,” Lucas says. “This is why it is often said that the plants are more resistant to pests and diseases – because of their adaptability.”

However, he notes that his trees in particular tend to produce smaller fruits because of the low rainfall. 

“This is possibly due to the [heavy] photosynthesis activity caused by the many sunny days,” Lucas says. “But ultimately, our coffees usually stand out for their sweetness and mild acidity.” This is a flavour profile which is often rare for robusta beans.

selection of robusta coffees

Fine robusta

While robusta is broadly perceived as being lower quality among the coffee community and associated with commodity coffee, higher-quality robusta can actually yield complex and delicate cup profiles.

Cleia says: “Fine robusta can have notes of tea, lemon, honey, vanilla, caramel, cocoa, walnuts, tea rose, coffee blossom, malt, coffee pulp, butter, raisins, raspberries, cinnamon, cloves, banana, and jackfruit.”

Lucas adds that things have changed dramatically regarding how robusta beans are scored in recent years. The Coffee Quality Institute has developed its own Fine Robusta Standards and Protocols for this exact purpose.

Before the development of these standards, he says, a “desirable cup profile” for fine robusta was simply a clean and smooth cup with a nice finish. Today, however, Lucas says that we can expect much, much more.

He says: “High sweetness, creamy body, and more exotic sensory notes, such as fruits, flowers, and spices, can lead a fine canephora to reach or even exceed the 90 point barrier!”

roasted robusta coffee beans in basket

How do you roast robusta differently?

Just like arabica, the flavours within robusta beans are unlocked by the process of roasting. However, as a different species, robusta beans behave differently during the roast, and roasters need to change their approach accordingly.

Density, shape, and sugar levels all come into play when profiling each new coffee. To bring out the best in each lot, roasters must consider these variables (and a variety of others) when developing a profile.

Firstly, density. Robusta beans are generally less dense than arabica, as they’re grown at lower altitudes and higher temperatures.

However, their bean structure is far more complex, so confusingly, during the roast, robusta actually behaves like a very dense high-altitude arabica coffee.

Lucas regularly speaks with other roastmasters about the processes they go through to get the best out of arabica beans, just to give himself some context.

He explains: “The theory behind is not very different [for arabica and robusta], but people have to take the same approach as when they start a new batch from a different origin.

“It is not possible to simply turn on the machine and repeat the last profile you use. The cellular structure of conilon [and robusta] is more rigid, and this makes it behave similarly to denser grains, even though the apparent density is not so high.”

As such, Lucas recommends starting with a higher charge temperature when roasting robusta.

He adds: “Heat is transmitted differently within the beans, which end up requiring slightly longer towers, and often, a final temperature 5 to 7 ºC higher than for arabica coffees.”

This difference in heat transmission means that the rate of rise (RoR) doesn’t change as much throughout the roast. As such, many roasters believe that robusta is much more “forgiving” than arabica.

Development & timing

Cleia says: “Robusta beans, because of their density, can be roasted for a bit longer without damaging their structure and taste.”

This means that longer development times are often better suited to robusta coffees, and may even bring out more desirable flavours. 

Roast times towards nine or ten minutes will bring out chocolatey and spicy notes in good quality robusta as the sugars start to caramelise.

It’s also important to point out that first crack is much less audible when roasting robusta. Taking extra care to pinpoint it will help guide your roast, whereas missing it can mean overdevelopment and bringing out more of the smoky or acrid notes in the beans.

ripe coffee cherry in fingers

What can you expect from robusta when cupping it?

Like Q graders, R graders use a specific score sheet to give the beans a point score out of 100. This then affects the premium that will be paid for it.

Robusta is generally seen as much less desirable than arabica, with unconventional or undesirable tasting notes. 

This is the main reason that arabica has dominated the market. Arabica’s balanced sweetness, acidity, and body have historically meant that the species has had much more appeal with wider audiences. 

Cleia says: “The flavours you will find in commodity-grade robusta include notes of potato, garden peas, pepper, cedar, pipe tobacco, toasted bread, roasted peanuts, earth, medicine, smoke, rubber, straw, wood, salt, and some astringency, too.”

Robusta is also often used in blends to add caffeine, crema, and body to the overall cup. However, Cleia says that if you’re blending, you should approach the roast differently.

“If you’re using it in a blend, the best thing to do is to split the roast to enhance the qualities of both the robusta and arabica,” she says. “You should also educate the clients about how fine robusta can create a better and bolder espresso beverage, for example.”

couple having coffee

Ultimately, you should keep in mind one golden rule when roasting robusta: don’t base your profile on any experience roasting arabica. 

The two species are fundamentally different, meaning that your expectations for everything from first crack time and RoR to charge temperature should change accordingly. However, with this in mind and some high-scoring robusta beans, prepare yourself for a surprise. 

Sweeter, subtle, and complex flavours are by no means impossible with robusta coffee – you just have to adjust your expectations.

Enjoyed this? Check out our article about robusta coffee’s genetic diversity.

Photo credits: Pixabay, Josef Mott

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