March 2, 2022

How can processing be used to improve the quality of commodity robusta coffee?


Robusta accounts for between 30 and 40% of global coffee exports, yet in major consuming markets, it is predominantly used in blends and soluble coffee. The main reason for this is the perception that robusta is of lower quality than arabica. But can that change?

Typically, robusta is treated differently to arabica when roasted. This is mainly because the cell structure of robusta beans is more rigid than arabica, so roasters need to take greater care with it.

The same attention to detail should be accounted for during the processing of robusta, especially as it’s estimated that post-harvest activities can be responsible for up to 60% of final coffee quality.

To learn more, I spoke to George Mhlanga from Bioroots and Lisbeth Ankersen from Innova Consult about developing standardised and high-quality processing methods for commodity robusta. Read on to learn more about what they said.

You may also like our article on exploring robusta coffee’s genetic diversity.

robusta green coffee beans

Robusta processing: An overview

Processing removes the layers – including the skin, fruit, mucilage, and parchment – which surround the coffee bean. It is a post-harvest activity which is ultimately necessary for the coffee to be roasted and subsequently ground and brewed.

George Mhlanga is a microbiologist and agronomist. He is also the owner of Bioroots ApS in Copenhagen, Denmark. He tells me that Bioroots has developed a unique processing method to improve the cup quality of robusta.

“There are several processing techniques used for robusta, which depend on the region and factors such as water availability, infrastructure, weather, moisture measurement, and storage,” he tells me.

While robusta originated in Africa, today most of it is grown in Vietnam, which accounts for some 40% of global robusta exports. Brazil is also well known for its robusta production, as are India and Indonesia.

Most robusta produced globally is processed naturally, as this technique is typically more affordable for smallholder farmers. 

With natural processing, the harvested coffee cherries are laid out to dry on patios or raised beds – with the skin, fruit, and mucilage left intact. This adds to overall sweetness and fruit flavours as the sugars are able to fully develop.

Alternative processing methods for robusta include the wet hulling process (also known as “giling basah”), which is frequently used in Indonesia.

This is where the coffee is washed and ferments to remove the pulp and skin (similar to washed processing), but is only dried to around 20% to 24% moisture. At this point, while the beans are still soft, they are hulled using a special machine, before then being dried to 10% to 13%.

Lisbeth Ankersen is the Director of InnovaConsult ApS, which specialises in examining and describing flavours in food – including coffee. She describes some of the common tasting notes found in robusta.

“The flavour notes typically found in robusta coffee are woody, earthy, and sour,” she says. “However, it’s not the presence of individual compounds that creates the overall flavour of coffee, but the combination of several compounds.”

Broadly speaking, these flavour notes are not considered to be desirable in coffee. However, as there is less interest in robusta quality worldwide, producers often don’t account for the difference in general flavour profile throughout post-harvest.

robusta coffee cherries

How does processing influence coffee quality?

Lisbeth takes me through the numerous phases of processing, all of which have an impact on final cup quality.

“There are different steps we go through with post-harvest for coffee beans, and they all affect quality and flavour,” she says. “We start with harvesting, sorting, pulping, and fermenting, before moving onto drying, storing, milling (hulling and polishing), and grading.”

At each stage, best practices and standards should be followed in order to produce coffee of the highest quality – much like with roasting and brewing. But as robusta is generally perceived to be of lower quality, it commonly receives less care throughout these stages.

George tells me that because robusta is inherently different to arabica, it should therefore be treated differently throughout processing.

“Robusta’s genetic composition means that it has higher levels of caffeine, chlorogenic acids, and other chemical compounds than arabica, all of which contribute to a more bitter taste.”

Processing and post-harvest should therefore account for these differences, and attempt to balance this inherent bitterness with sweetness and acidity. 

Ultimately, when robusta is grown and processed to higher standards, farmers can produce fine robusta: an industry term used to define high-quality robusta. 

To be considered “fine”, robusta must be free of primary defects and display characteristics which are unique to its origin. 

“Handpicking robusta ensures only the ripe beans are picked, resulting in higher cup quality,” George explains. 

“Sorting also affects the flavour of the beans,” Lisbeth adds. “Various defects can generate different off-notes in the coffee.”

In recognition of the rising quality of fine robusta, the Coffee Quality Institute and Uganda Coffee Development Authority have co-developed guidance for producing it. This is known as the Fine Robusta Standards and Protocols, which includes a list of common defects found in robusta coffee. 

To be classified as fine robusta, beans should have no primary defects, including fungus or mould damage. 

The coffee beans should also have no more than five secondary defects, which include broken or cut beans, small levels of insect damage, and floaters (a sign of unripe coffee beans).

George points out that any coffee can suffer from low quality when there is lack of consistency and attention to detail with processing, irrespective of its species. “Poor processing can also affect the quality of arabica coffee, just as it often has done with robusta.”

However, by the same token, Lisbeth notes that in the future, processing could allow robusta producers to potentially improve the cup quality of their crop.

“Processing has the ability to change the flavour profile of ordinary robusta, and increase the consumer’s overall enjoyment of it.”

fine robusta coffee

Improving robusta processing methods

Washed processing is a common technique used to remove all skin, fruit, and mucilage from beans. It produces a cleaner tasting coffee; for arabica, it often yields a brighter cup profile with more noticeable acidity.

However, washed processing is more difficult to carry out for robusta. This is because robusta beans have thicker layers of mucilage than arabica, which increases the risk of overfermentation. Robusta mucilage is also stickier than arabica mucilage.

To avoid overfermentation, producers usually have to wash their robusta for more than 72 hours. In addition, the lower the elevation the robusta is grown at, the greater the risk that it will overferment. 

Too much fermentation can lead to off-flavours, such as strong notes of alcohol or medicine, or even cause mould and bad bacteria to develop. 

So, how can producers improve robusta quality while minimising this risk?

“For more than five years, Bioroots has worked to develop a process that can help to achieve a higher-quality robusta coffee,” George says. He adds that this process is easy to use at scale, and works for farms of all sizes.

Lisbeth starts by talking about how the proprietary Bioroots processing method uses fermentation.

“The first step of fermentation, which occurs as soon as the cherry is picked, is responsible for generating many of the 900 different flavour compounds found in coffee,” she tells me. “We have then added a second step for the Bioroots process.

“In this second step, the specific enzymes of the fermentation microorganisms digest some of the carbohydrates in coffee and transform them into desirable flavour molecules.”

George explains how this changes the flavour profile of the coffee.

“The process produces robusta coffee with flavour profiles that can be similar to that of arabica coffee, with notes of chocolate and bell pepper,” George says. “These results have been noted through several cupping tests by established institutions in different countries, which have also provided sensory profiles for Bioroots robusta.

“The process is also designed to work in batches, which makes quality control easier,” he adds. “This means it is more cost-effective. It is also natural, and does not use chemicals.”

However, improving robusta quality doesn’t just end at processing – it carries on to roasting and brewing.

“Since developing this processing method, we have worked with several roasters to create a roast profile that takes into account the lower levels of acidity in robusta,” George explains. “The profile has been tailored to fit the Bioroots robusta’s requirements, and seeks to preserve the acidity, leading to a brighter, fresher cup.

“Using the process, we can definitely create two different robusta coffees with unique and distinctive flavours, and it is possible that we will create a third,” he adds. “We’re now ready to use it at scale with partners, and in my opinion, I think these coffees could change people’s perception of robusta being inherently inferior to arabica.”

harvesting robusta coffee

How can this benefit farmers?

“The use of robusta coffee beans is limited in the wider coffee industry,” George says. “Only 20% of all robusta produced is used in blends with arabica, and even then, the purpose of these blends is to mainly dilute the cost of arabica.”

George adds that because robusta relies on cross-pollination to breed, it is incredibly genetically diverse, but this can be detrimental if not monitored carefully.

“The challenge with robusta hybrids and cultivars is that it’s difficult to trace genetic histories of certain hybrid varieties,” he says. “This makes it difficult to grow a variety of recognised quality.”

However, as robusta comprises 30 to 40% of all coffee exports, improving its quality more broadly could have major implications for the wider coffee sector.

“Robusta can be grown in some areas where arabica cannot grow,” Lisbeth explains. “The possibility of high-quality robusta creates new possibilities for producers seeking higher prices.”

Robusta is generally more resilient than arabica, meaning it can grow at lower altitudes. It is also more resistant to a wider variety of pests and diseases. Furthermore, with recent research indicating that major coffee-growing regions could become much less productive by 2050 due to climate change, the need for more hardy coffee varieties and species is becoming more necessary.

“The market for robusta coffee beans is limited, but it could be increased,” George says. “If we were to do this, we would have a plentiful supply, because robusta plants have higher yields.”

It’s estimated that 1ha of robusta plants can produce around 6,000kg of coffee – significantly more than even the most productive arabica varieties. It’s yields like these that ultimately led to Brazilian robusta exports increasing by a staggering 59.5% between 2018 and 2019. If the market scales, farmers could see their margins and income change dramatically.

But it’s not just producers that could benefit from improving robusta quality. Lisbeth notes that in time, continued focus on robusta quality could lead to more consumers regularly drinking it.

“In our consumer test, we found that a sample of the Bioroots double fermented robusta coffee was preferred over a sample of arabica coffee,” Lisbeth says. “However, a combination of the two was ultimately preferred by most.”

roasted robusta coffee

Although growing, harvesting, and processing can help to improve robusta quality, to maintain these improvements, we need consistency down the supply chain.

George concludes: “In order to change the perceptions of robusta as a lower quality coffee, more effort must be made to educate and inform baristas about the potential flavour profiles of fine robusta coffee.”

Enjoyed this? Then read our article on roasting robusta coffee.

Photo credits: George Mhlanga

Perfect Daily Grind

Please note: Bioroots is a sponsor of Perfect Daily Grind.

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