Chapter 22 - Coffee

Abstract

In this chapter, it is shown how spectroscopic techniques can be applied for the discrimination of different types of coffee and of their geographical origin. In a first approach, a study on the application of Raman spectroscopy to the differentiation of coffee type (Arabica vs. Robusta) is described, based on the determination of kahweol content, wherein the results obtained allowed coffee type discrimination. Then, isotope ratio mass spectrometry (IRMS) is addressed as a tool for the determination of the isotopic composition of carbon (C), nitrogen (N) and oxygen (O) of the green coffee bean, allowing coffee differentiation at continental level. Studies involving isotope analysis of the coffee bean have shown that oxygen is a fundamental element to achieve this differentiation, reflecting the hydrology of the coffee-producing regions. Subsequently, IRMS has been combined with inductively coupled plasma mass spectrometry, to determine the isotopic composition of strontium (Sr) in the coffee bean, in particular the ratio of the isotopes 87 and 86 (87Sr/86Sr). The study demonstrated that the isotope ratios of Sr and O can be promising for coffee authenticity, as these elements reflect the local geology and hydrology. However, in order to expand the understanding of how environmental factors determine the isotopic composition of the different elements in the green coffee bean, it may be necessary to study a model region of production, such as Hawai’i. A study performed at microscale, with coffees from different Hawai’i islands, allowed the detail analysis of how the various environmental factors prevailing in the location and time of coffee production were reflected in the elemental isotopic composition of the coffee beans. This approach allowed the discrimination of coffees from the different islands of Hawai’i. It has also revealed that the isotopic composition of O, Sr and S in the green coffee beans is related to known environmental factors, namely, the isotopic composition of the O of local precipitation (δ18Oprec), the distance to the coast and the volcanic activity characteristic of that region. In short, this chapter describes the various tentative approaches to coffee geographical origin discrimination where isotope analysis may play an important role and also, how this tool can bring an additional value to each coffee (or provenance), an ecological value.