December 2, 2015

Controlled Fermentation: A Critical Step in Flavour Development?


If there’s one thing that we’ve got wrong about coffee, it’s fermentation. Traditional ways of thinking about coffee processing state that this stage has no major impact on the development of the flavor profile (or taza, as we like to call it in Colombia). Yet that couldn’t be more wrong.

Here at La Palma y El Tucan we’ve spent the last three years studying coffee fermentation. Our conclusion? Fermentation is the most critical step in the development of flavor.

So read on as we explain why fermentation is more important than you realize – and how you can manipulate it to see excellent profiles.

Spanish Version: Fermentación Controlada: ¿Un Paso Crítico para el Desarrollo del Sabor?

The Confusion Over Fermentation

So many of our luxury food and beverage items involve controlled fermentation: grapes for wine, olives for oils, pickles and cabbage for sauerkraut, hops for beer, cocoa for fine chocolate… So the fact that fermentation is an important step really shouldn’t be surprising. Yet it is. Why?

Fermentation process

The process of fermentation is crucial not only for coffee beans and has to be monitored closely.

Fermentation is an important step in coffee processing: it’s the natural removal of the mucilage as opposed to removal-by-machine. For years, many have argued that mechanical removal will result in a “comparable quality” with fermented coffee.

The problem with this is the tricky act of defining “quality”.

Defining Quality

After thirteen years of working as a consultant in the coffee industry, I’ve learned that “quality” will always be subjective. Sure, you can look at measurable factors, such as size, moisture level, and defects. Yet ultimately, coffee is a business, not a science. Quality will always be defined by the expectations of the consumer and the capabilities of the producer to meet those expectations. In other words, coffee quality is a narrative agreement between seller and buyer.

With both “quality” and “comparable quality” being so subjective, it’s no wonder that people have been unable to notice the difference between fermented and non-fermented coffee. The combination of factors like confirmation bias and a lack of manipulation of the fermentation process means that, well, it’s just hard to tell the difference.

sorting coffee cherries for fermentation

Hand-sorting coffee cherries is another way to improve the quality of your lot.

Flavor Profiles: The Reason Fermentation Is Important

In this world where coffee quality is decided by consumers’ expectations, flavor profile will always be the primary measurement of it.

In many ways, flavor profiles can be subjective. The ideal profile could be the classical clean cup preferred in conventional markets – or it might be the distinctive and complex sensorial experiences found in specialty niches.

Yet the science behind flavor is also pretty objective. Let’s break it down.

What is flavor? Flavor in coffee is the sensory impression (normally taste and smell) of a coffee infusion.

What makes flavor? Flavor is determined by the reaction of those senses of taste and smell to certain chemical compounds, such as sugars, organic acids, lipids, alkaloids, proteins, and so on.

Fermentation in coffee

Fermentation has a big impact on the flavor profile of the final cup.

So what does this have to do with fermentation? Well, those chemical compounds that make up flavor are the same compounds that react and change during coffee fermentation. When fermentation occurs, microorganisms – including yeast, bacteria, and fungi – degrade and metabolize carbohydrates (sugars) to produce energy (ethanol and carbon dioxide). In this process, additional compounds are generated, including organic acids. Notice the overlap?

And here’s the reason why fermentation is so important: if you could understand and control these reactions during fermentation, you could develop and modulate coffee´s sensory impression. Take acidity and mouthfeel. These are both profoundly affected by the concentration of organic acids. Manipulate those and you manipulate the flavor profile – for better or worse.

SEE ALSO: Everything You Need to Know About Honey Processing

Manipulating Flavor Profiles Through Fermentation

Over the last three years, we’ve conducted a LOT of experiments. Our seemingly endless testing, documenting, and cupping has been done with the aim of working out which microorganisms are beneficial, which ones are bad, and how to manipulate them – all in the name of creating exceptional coffee.

coffee research

Continuous research is an important factor to improve your coffee production.

Let’s be clear about this: the fermentation of coffee is a highly complex process. Different types of microorganisms interact with natural mucilage in very diverse ways, some of which will be simultaneous and some of which won’t be. Climatic conditions, particularly temperature and humidity, will also affect the process.

Basically, there’s no one-size-fits-all Coffee Fermentation for Dummies guide on the way.

However, we did discover that six environmental conditions will determine which microorganisms are present at different stages of fermentation, thereby affecting the final product.

So what are these environmental conditions?

  1. Sugar concentration (Brix)
  2. Amount of available water (Aw)
  3. Availability of Oxygen
  4. Temperature
  5. Potential Hydrogen (pH)
  6. Time (Cut Variable)
Coffee research

Sugar concentration in a coffee cherry can be measured with a brix.

Our experiments have led us to a standardized fermentation protocol that allows us to control the flavor profile of the final cup. We’ve learned how to find a balance between acetic acid microbes and lactic acid microbes, meaning that we can develop and modulate the flavor profile of our coffees – and guarantee consistency.

The Future of Coffee Fermentation

Our goal now is to gain a better understanding of how managing the wide variety of variables and conditions impacts on the coffee. The sheer number of microorganisms and the difficulties in accurate identification and classification make this difficult, but we’re determined to deepen our knowledge of the chemical reactions.

To achieve this, we’ve begun conducting chromatography and spectrophotometry trials with a local university. This will help us discover the precise type of microorganisms present at the different stages of fermentation, and the exact concentration of compounds produced by the microorganisms responsible for the final flavor profile. This knowledge will enable us to standardize new fermentation methods and exotic flavor profiles.

Never take anything for granted. Question any idea that isn’t evidenced. And when you have a theory, conduct experiment after experiment to test it. This is our philosophy, and it has allowed us to make these breakthrough discoveries. I invite you to adopt the same philosophy.

Perfect Daily Grind