Difference Spectroscopy in the Analysis of the Effects of Coffee Cherry Processing Variables on the Flavor of Brewed Coffee

Infrared difference spectroscopy was used to study how changes in the processing of Arabica coffee cherries into green beans affected the flavor of coffee brewed from roasted green beans. Paired samples of green beans, in which the drying step or fermentation/washing step in their processing was altered, were roasted and brewed in a standard manner and their ATR-FT-IR spectra obtained. Difference spectra of the 1800 to 1680？cm？1 carbonyl region of water-subtracted spectra of paired samples of these brewed coffees provided data which indicated differences in brewed coffee flavor due to changes in fermentation/washing steps and drying steps involved in the processing of coffee cherries. The role of acid, ketone, aldehyde, ester, lactone, and vinyl ester carbonyl components on the flavor of brewed coffee is proposed that is consistent with the flavors as perceived by the coffee tasters. 1. Introduction The blending of taste from volatile and nonvolatile compounds sensed in the mouth and aroma from volatile compounds sensed in the nose gives brewed Arabica coffees their distinct flavor [1–4]. All Arabica coffee cultivars are derived from two original, or heirloom, varieties, the Typica and Bourbon. Mutations and hybrids of Typica from the Amsterdam Botanical Garden and Bourbon from the island of Bourbon are now grown worldwide resulting in significant variation in the flavor profiles of coffee brewed from them. Factors influencing coffee flavor are the species of coffee cultivar, the geographical conditions where the cultivars are grown (including type of soil, climate, and altitude), methods used to process coffee cherries into green beans, and how the green beans are roasted. Processing variables involved in converting the coffee cherries into green beans appears to be of major importance. In an effort to improve the overall taste of their coffee beans, some coffee plantations are exploring ways to tweak the washing and drying of coffee cherry processing. Normally, determining the effect of these changes rely on taste testing of coffee brewed from roasted green beans. Taste tests are subjective, and a more empirical analytical technique to assess the effect of these variables on the flavor of brewed coffee is of interest, particularly one that sheds light on the molecular changes that produced the perceived flavor differences. Difference spectroscopy was initially developed to characterize reaction-induced changes in protein conformation by assessing differences between a sample spectrum and a reference spectrum. It was later used to show how changes in