How to Ensure Consistency in Coffee Fermentation & Processing

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Bread, wine, cheese, yogurt, chocolate, coffee: what do all of these delicious items have in common? Fermentation.

In coffee, fermentation is crucial. It doesn’t just allow the removal of mucilage but also affects a lot’s flavors and sensory characteristics. Having control over it during coffee processing means that you can increase quality and consistency.

Yet fermentation is complex and managing it at the farm level can be a challenge. To learn more about how producers can handle this, I spoke to experts at Lallemand, a company specializing in fermentation in food and beverages, and several of their partners.

You might also like: How Does Fermentation Affect Coffee Flavour Development?

Pulped natural coffee dries on a raised bed under the sun. Credit: Capricornio Coffees

What Is Fermentation in Coffee?

Fermentation is a natural process in which microorganisms such as yeasts (Saccharomyces cerevisiae) and bacteria (Lactobacillus) consume and metabolize compounds such as sugars and acids within the cherry. As a result, these compounds are broken down into acids and alcohol.

But why do we ferment coffee? First of all, for washed coffees, it is necessary for the non-mechanical removal of the mucilage.

Francine Vidal is the Coffee Project Manager at Lallemand LALCAFE, the branch of Lallemand that provides yeasts and bacteria for the controlled fermentation of coffee. The company offers several types of yeast with different effects on the coffee profile, ranging from mouthfeel to acidity and specific fruity or floral notes. “During this coffee fermentation or maceration, yeasts can degrade the mucilage from the beans,” Francine tells me. “This type is called demucilagination.”

Discover more in The Anatomy of a Coffee Cherry

Yet she also explains that fermentation is crucial because it affects the flavors and aromas that are developed in the cup.

“Mucilage is composed of sugar, amino acids, aroma precursors, and so on,” she tells me. “So, if you want to reveal and express the potential of aromas in the beans, you have to take care of that.”

Remember how sugars and acids are broken down during fermentation? It’s these very same reactions that make up flavor. If the sugars and acids break down under controlled circumstances, within suitable temperatures and time frames, the flavors and aromas developed in the bean will be more desirable.

Coffee ferments during washed processing. Credit: Capricornio Coffees

Good vs Bad Coffee Fermentation

Francisco Quezada is the CEO of Montenegro Farms in Guatemala. He tells me, “With good fermentation, you can draw out the characteristics that a coffee has. In other words, good fermentation will not elevate a coffee’s quality, because coffee already has its quality from the field. But we can draw out and maintain those characteristics that come from the field.”

Yet fermentation isn’t always good. “A bad fermentation, this lowers or produces bad qualities in the coffee,” he stresses.

“In an over-fermented coffee, what we find are wine flavours, but those of wine that has gone bad,” he says. Even before he cups the coffee, he can recognise the signs of over-fermentation: the beans have a reddish color and the unappetising aroma of rotting fruit.

For these reasons, it’s imperative that producers understand fermentation and can control it as much as possible.

Freshly picked, ripe coffee cherries in buckets, waiting to be processed and fermented. Credit: Mauricio Villegas

Consistency: Almost as Important as Quality

Luiz Roberto Saldanha, Owner of Capricornio Coffees in Brazil, tells me that consistency is also essential for accessing markets and seeing repeat purchases.

“If you don’t have a consistent product, it’s super difficult to make long relationships,” he says. He tells me to imagine if a buyer came back to a producer after buying a beautiful lot of coffee. Probably, he says, the buyer will be expecting the same qualities in their coffee the second time around. But they don’t receive the coffee they were expecting.

“So, then you started a relationship that you cannot keep going, your clients are not going to receive your coffee any more and you close the door and it’s super difficult and expensive to open it again,” Luiz explains.

One of the reasons why fermentation can be so challenging is that it’s the result of chemical reactions between microorganisms such as bacteria, yeast and fungi. And, according to Lallemand LALCAFE, these are essentially everywhere: in the soil, in fruits and berries, and as spores in the atmosphere. Under different circumstances, their reactions will change, modulating in different ways the flavors and aromas in coffee beans.

Yet consistency in fermentation is achievable. Mauricio Villegas has a PhD in Agronomical Engineering, has worked at Finca La Esperanza in Colombia, and is currently working on yeast trials. He tells me, “It’s not random. Simply, it’s that you have to define and control certain aspects to obtain more repeatability, and that repeatability will result in that [same] cup profile.”

Pulped natural coffees dry stage under the sun. Credit: Capricornio Coffees

How to Ensure Consistency & Quality in Fermentation

So, which factors should producers pay attention to in order to control fermentation and ensure consistent, quality coffee?

1. Cherry Quality

Margaret Fundira, Product Manager at Lallemand LALCAFE, tells me that the quality of the harvest is fundamental. “The quality of the raw material or cherries is important. Yeast [in fermentation] can only work with what is available in order to reveal or enhance certain aroma compounds due to their different metabolic processes,” she says.

Luiz Roberto agrees and explains that plants need minerals, nitrogen, and amino acids. “The only way to provide this is having a health plan where you decrease the stress and you [create] better conditions in order to grow and develop the cherry,” he advises.

“So, you need to apply everything in the field to have a good cherry, and when I say everything, it’s absolutely everything: nutrition, plagues, and diseases management to take care of the plant, and the amount of water, shade, and pruning.”

Coffee laborers with their freshly picked cherries at Fazenda Capricornio in Brazil. Credit: Capricornio Coffees

2. Cleanliness

Microorganisms are everywhere, and they aren’t all good for your coffee. Luiz Roberto explains that coffee cherries “already have microorganisms adhered to their surface, as well as the soil, harvesting materials, hands of the workers and infrastructure of transport, reception and processing.”

These, he says, can lead to contamination.

While it’s impossible to have a microorganism-free farm or mill, cleanliness can help greatly. Washing tanks should be cleaned after use. So too should all the tools used.

3. The Presence of Oxygen

Mauricio tells me that there are two types of fermentation: aerobic and anaerobic.

In aerobic fermentation, oxygen is present, which contributes to the respiration and growth of microorganisms. “Aerobic fermentation is the one that has been conventionally used,” he explains. “Nevertheless, that is a fermentation process in which you have less control of what is happening.”

This is because there are microorganisms everywhere, and the oxygen affects their growth in a way that can be hard to predict and control.

In anaerobic fermentation, Mauricio explains that the coffee is usually placed in a closed tank with no oxygen presence and a valve for the release of carbon dioxide. This gives producers more control over the chemical reactions happening.

Washed coffee ferments in a plastic tank. Credit: Mauricio Villegas

4. Microorganism & Yeast Type

Different yeasts and microorganisms will have different effects on the fermentation process. For example, Lallemand LALCAFE uses the yeast Saccharomyces cerevisiae for all of their products. However, depending on the strain used, the yeast can have a different impact on the coffee: one can “enhance the fruity flavor (apricot, passion fruit, flower notes, vanilla), the mouthfeel of the coffee and the final cup quality;” another, the “brightness and citrus notes… [and] the mid-palate mouthfeel;” while a third one “is often preferred when processing time and efficiency is a priority.”

Mauricio also tells me that he has been conducting experiments with Lallemand LALCAFE’s yeasts. In his trials, the added yeasts overcame the indigenous or native microorganisms during the fermentation process, resulting in more controlled fermentation.

“When you use microorganisms in a population where you saturate the fermentation tank, you can obtain more consistency and cleaner cup profiles than compared to when you ferment with random processes and you don’t know what is really affecting the fermentation,” he explains.

Washed coffees ferment in a tank, with an added yeast product affecting the processes that take place. Credit: Lallemand LALCAFE

5. Time & Temperature

These two factors are critical because temperature affects the rate of fermentation. “When the fermentation process within the bean is taking place under 20ºC, then I can take that fermentation up to 36 hours,” Mauricio explains.

On the other hand, at higher temperatures, he tells me that fermentation tends to happen faster – often too fast. “It is possible that after 24 hours, I can already have problems that will appear as defects in the cup”.

Measuring pH and temperature during fermentation. Credit: Montenegro Farms

6. Data & Records

Without recording data and processes, it is harder to follow the same protocols in the future. From the temperature of the harvest season to the time of day at which the coffee was harvested and the length of the fermentation process, every piece of data is useful.

Be sure to measure pH levels, which indicate how acidic your coffee is. Record your Brix levels, which Luiz tells me won’t only let you know the amount of sugars present in your coffee but also the amount of substrate or food that bacteria and yeasts are feeding on.

“If I don’t have data or a process or I don’t know the background, I don’t have a way to do it again… So to obtain repeatability, you indisputably have to measure and know how variables behave during the process,” he says.

“And you definitely you have to know the temperature flux or behavior during fermentation, the dynamic of the Brix levels during fermentation, and the dynamics of the acidity on the mucilage during fermentation, because based on that, you can make decisions or even abort the process.”

Coffee dries on raised beds on Fazenda Capricornio in Brazil. Credit: Capricornio Coffees

Every Coffee Is Different

But remember: even those these six factors are key for consistent, high-quality coffee, you can’t treat every lot the same way.

“There are varieties with which you can work with different fermentation processes, long or short, with higher or lower temperatures, with the addition of microorganisms or without them,” Mauricio says.

So, know your coffee well. Take into account the varieties you have and the flavors they usually possess. And also make sure you know your farm, from the soil to the local climate.

Luiz emphasizes the importance of understanding which processing method works best in your region. If you work in a wet or cold region, natural or dry processing might not be a good idea. “On the other hand, if you have a dry region with sunny days and low moisture, you can play with the dry process,” he says.

“You need to understand how microbes are going to behave according to these conditions of the environment, having in your mind: fermentation starts in the crop and it finishes in the drying process.”

A coffee laborer with freshly picked, ripe-red cherries, in which fermentation will have already begun. Credit: Capricornio Coffees

Fermentation is a topic that’s not yet widely understood, but it can have far too significant an impact on coffee quality for us to ignore it. Francisco tells me, “We have to leave the fear behind and start experimenting so we can have better results and better characteristics in the coffee.

“This is part of the crisis we are living,” he adds. “Something that can save us is having that consistency in our products and so augmenting their quality with more controlled processes throughout the production chain.”

After all, as Luiz says, “So, why is consistency so important? To aggregate value to the production. To decrease the amount of low commercial rates and increase the amount of specialty coffees, and find new markets.”

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