Yeast Fermintation and Quality Trends in Coffee Processing

Yeast Fermentation and Quality Trends In Coffee Processing

by Matthew Dahabieh, Ph.D and Jason Hung, M.Sc

Unlike wine and beer, coffee fermentation methods remain mostly unknown to many consumers of the drink, many of whom are unaware that coffee is even a fermented product. Of course, rare yet well-known niche fermented coffees do exist; for example, Kopi Luwak and Black Ivory coffee are two of the world’s most expensive choices, due primarily to their unique processing method (namely, fermentation inside digestive tracts of the Asian palm civet and Asian elephant, respectively).

In the coffee mainstream, the concept of fermentation and, more specifically, the harnessing of fermentation as a tool for improving consistency, quality and specialization, is still very much in its infancy. It is ironic that, while the rest of the coffee production process has become refined and sophisticated (using sensors, automation, and artificial intelligence, no less), coffee fermentation hasn’t progressed much outside of literally hand-picking coffee beans after an animal has “processed” them.

Almost all coffee goes through a fermentation process, but not typically in an animal’s digestive system. The main methods are wet and dry processing. In the case of Kopi Luwak and Black Ivory coffee, while the animal is partially responsible for processing, it is gastrointestinal microbes that do much of the work. Likewise, in the cases of both conventional wet and dry processed coffees, spontaneous fermentation of the beans is facilitated by wild microbes, e.g., bacteria, yeast and filamentous fungi 1 . These microbes not only assist in the removal of the mucilage layers surrounding the coffee bean, but they also produce some of the flavor precursors expressed during roasting and brewing.

The effect of fermentation on the flavor and aroma of coffee has measurable impacts on the cupping score of coffee 2 . Once roasted and brewed. For example, coffee beans processed via the wet method had a superior aroma profile highlighted by fruity and floral aromas, while mechanical processing (without fermentation) contained many unpleasant chemical compounds 3 . One study looking at adding a yeast starter during dry processing found that some yeast produced higher sensory scores, and ultimately a higherquality coffee with aromas of caramel, herbs, and fruits; others did not 4 . This difference is primarily because different microbes consume and produce different chemical compounds that are converted into volatile compounds that comprise coffee’s unique sensory characteristics. This parallels the production of wine, in which it is an established fact that the local microbiome is an essential factor in terroir 5 .

Taken to the next level, the obvious parallels between coffee processing and wine production provide a potential competitive advantage to forwardthinking coffee producers seeking to improve their consistency, quality, and flavor. For millennia, fermented beverages such as wine, beer, and spirits were also produced through spontaneous fermentation. Sometimes this yielded fantastic results, but in many cases the product was undrinkable. For example, one common contaminant in spontaneous beer fermentation is Brettanomyces (commonly called Brett) 6 , characterized by aromas of “horse blanket” or “barnyard”, among other unusual descriptors 7 .

Today, coffee processing operates mainly in the spontaneous fermentation “black box” of uncertainty that has plagued wine, beer, and spirits production for centuries. While coffee producers and scientists are fully aware of the impact of coffee fermentation, what actually goes on during the process and, more importantly, what microbes are good, bad or even important, are not fully understood.

Since the 19th century, however, the wine, beer, and spirits industries have been continually refining and developing their fermentation processes. Today, the use of techniques such as strain isolation and domestication, and selective breeding and adaptive evolution, have further optimized Saccharomyces yeast strains to the point that modern brewers and vintners have at their disposal style-specific Saccharomyces strains that contain the positive attributes of several strains but produce none of their faults. Besides, high-throughput non-GMO yeast development techniques are now being applied to quickly develop large numbers of novel beer yeast strains with improved flavor and aroma profiles while still maintaining overall fermentation performance 8 .

A focused effort in developing and utilizing coffee-specific Saccharomyces and other microbial strains should deliver similar quality improvements. First and foremost, using predetermined, pure and optimized microbial strains will allow the coffee farmer and producer much more control, consistency and specificity in their products. This also means they could modulate green coffee beans to suit changing consumer preferences or capitalize on current trends without significant infrastructure changes — such as planting new coffee cultivars or establishing new plantations.

For larger organizations that source coffee beans from multiple farms and/ or co-ops, often from multiple locations around the world, standardization of the coffee fermentation process should produce more consistent green coffee, resulting in less variation in roasting and brewing (especially when factoring in different locations and roasters). In turn, more consistent green coffee ultimately reduces the need to store and blend coffee from multiple locations while still meeting consumer brand expectations.

Optimizing coffee fermentation will also enable farmers and producers to express the full range of flavor and aromas possible from their plantations and coffee trees. For example, farmers can use selected yeast(s) to highlight a specific flavor and aroma profile or accentuate a trait already valued in their product. Furthermore, batches of the same coffee harvest can be fermented with different sets of microbes to highlight specific roasting and brewing methods, e.g., coffee farmers could process green coffee beans differently if destined for drip coffee rather than espresso.

Without the use of pure, optimized fermentation cultures, vintners, brewers, and distillers would not have been able to diversify, expand, and add value

to their products, and the beverage industry would look very different than it does today. Again, the commercial trajectory of coffee parallels that of wine and spirits as coffee has started to shift from a necessary commodity to an affordable luxury. In fact, the National Coffee Association’s 2017 National Coffee Drinking Trends report highlights that, for the first

time in the report’s 67-year history, more than half (59%) of all consumed coffee in the United States falls under the “gourmet” category 9 .

As with all luxury products, there is an increasing trend to highlight to consumers the care and attention that farmers, roasters, and baristas put into their product. Unfortunately, coffee fermentation, and its role in and impact on coffee quality, has largely been left out of this discussion. In reality, this is because no one yet understands what makes for good coffee fermentation, or what microbial strains would be most beneficial in terms of yielding overall flavor and aroma improvements. However, the modern tools and expertise needed first to determine the relationship between coffee and microbes, and

then to leverage that information into the development of coffee-specific fermentation yeasts are both feasible and available.

There is no hyperbole in saying that today’s yeast scientists have the ability to develop Saccharomyces yeast strains that feature any combination of desired traits. All that’s needed in the mix is the creativity, ingenuity, and vision of coffee farmers, roasters and baristas to see what’s possible through targeted and consistent coffee fermentation. Then add in a dash of desire to produce better-quality coffee. What you end up with are possibilities for coffee lovers that are limited only by the bounds of imagination.

About the authors: Matthew Dahabieh, Ph.D, is Chief Science Officer of Renaissance BioScience Corp. while Jason Hung, MSc., was Associate Science Writer at Renaissance BioScience Corp. _______________