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Pursuit of superior flavor and taste Finding a metabolite indicator to predict taste from raw coffee beans

Coffee beans are grown all over the world by different cultivars and producing centers. Unfortunately, we have no way of choosing beans with superior taste without roasting them and then actually drinking the resulting coffee. In an effort to identify the potential for outstanding flavor in raw beans, Suntory studied the metabolites in high-quality beans and developed a method to predict taste based on their characteristics.
It is generally held that the riper the beans at harvest time, the better the resulting coffee tastes. In studying the broad range of metabolites found in raw beans, Suntory found that the maturity of raw beans could be predicted by looking at the amount of tryptophan they contained. We also discovered an isomer of 3-Methylbutanoyl Glycosides in raw bean metabolites, and found that raw beans with high glycoside content tasted better when brewed. This groundbreaking research by Suntory gave the world critical insight into the science behind a truly delicious cup of coffee.

Raw coffee beans

Objectively evaluating taste from raw coffee beans

Sensory analysis (human taste and smell) has been used to evaluate the taste of coffee beans. However, because each person is different in terms of their sensitivity, factors like evaluator training and environmental design are critical if these studies are to produce reliable results. To overcome these limitations, Suntory sought to create an objective scale of taste not dependent on human sensation. Coffee flavor is generated from changes in a vast number of metabolites when raw beans are roasted. Working off of the idea that the kind and amount of metabolites in raw beans determine the taste of brewed coffee, Suntory set out to find the key metabolite that could predict coffee quality from raw beans.

Roasted coffee beans (left) and raw beans before roasting (right)
Roasted coffee beans (left) and raw beans before roasting (right)

Analyzing thousands of metabolites

Raw coffee beans contain many kinds of metabolites in different amounts. However, the ones that have the most impact on the taste of brewed coffee are sometimes those found in the lowest amounts—so studying them required a sophisticated technique for measuring metabolite content in raw beans. Through a collaborative project with Dr. Hiroyuki Wariishi at Kyushu University’s Faculty of Arts and Science, Suntory was able to adopt a technique called metabolomics—a medical diagnostic technique that uses metabolite information from a small amount of blood and saliva to identify diseases. This innovative method made it possible to analyze even the subtlest differences in thousands of coffee bean metabolites.

Coffee bean ripeness, metabolite level, and taste

Since riper beans at harvest typically produce better coffee, Suntory’s hypothesis was that the amount of some key metabolite was dependent on the ripeness of the coffee fruit. To test it, we harvested coffee fruits at four different levels of ripeness from nine cultivars in a coffee field at the Hawaii Agriculture Research Center. In our joint research project with Dr. Chifumi Nagai at the center, we used metabolomics to analyze the components of the raw beans and discovered that immature fruits contained higher amounts of the amino acid tryptophan, and that this amount decreased as they became riper.

Tryptophan is known to be the precursor of auxins in corn and rice, but Suntory’s trailblazing research revealed for the first time that it plays a significant role in coffee maturation as well. Our pilot experiments on roasting also revealed that tryptophan is a precursor of the indoles that cause the unpleasant, unripe odor in poor-quality coffee. These results confirmed that the tryptophan in raw beans negatively impacts the taste of brewed coffee.

Coffee trees at the Hawaii Agriculture Research Center
Coffee trees at the Hawaii Agriculture Research Center
Nine cultivars of harvested coffee fruits at four levels of ripeness
Nine cultivars of harvested coffee fruits at four levels of ripeness

Discovering a new compound that creates rich-tasting coffee

Thanks to metabolomics, we were able to go further with our coffee research to identify two isomers of 3-Methylbutanoyl Glycosides in raw beans, one of which is the novel structure in a world first. Further studies confirmed that coffee made from raw beans with these isomers tasted better. Suntory was therefore able to create a method for identifying the raw beans that would brew the most delicious coffee by tracking tryptophan and the isomers of 3-Methylbutanoyl Glycosides.

Analysis of minor components using precise analytical devices
Analysis of minor components using precise analytical devices

Selecting the perfect beans

The results of our study make it possible to develop a technique for selecting only the finest coffee beans while they are still raw—and it may also become possible to adjust the relative amounts of the components that determine taste. Generally, the quality of coffee beans is based on seller criteria, such as distribution prices and the grades given to different production areas. If we, as buyers of raw ingredients, have our own indicators to judge taste, we will be able to develop products that take advantage of certain bean characteristics. Suntory will continue its research with the goal of eventually creating our own delicious coffee beans in our ongoing endeavor to create ever more delicious coffee.

Related link
[News Release] Chemical Compounds in Green Coffee Beans Predict Precisely the Quality of Coffee Beverage (Apr. 16, 2015)
[News Release] World's First Elucidation of the Strong Correlation between Tryptophan in Coffea arabica green beans and the Maturity Level of Coffee Cherries, a Determinant of Coffee Flavor Quality (Sept. 11, 2014)
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