by Roberto Zironi
He is professor of Food Industries at the University of Udine and president of the Department of Food Science in the same University. In addition, he is the chair of the scientific committee of the International Institute of Coffee Tasters and vice-president of the International Academy of Sensory Analysis.
The definition of specific markers which describe a coffee all throughout the production process makes it possible to monitor and optimize both its hygienic-sanitary and sensorial quality so that levels of acceptability can be set and anomalies in the composition of the final aroma can be spotted.
Among the various components which contribute to the creation of the aromatic profile of a coffee it is not easy to establish which of them can be defined as markers of quality in that it is necessary to mediate between the characteristics seen as related to the specific coffee and the place of origin and the market needs.
In order to identify the markers of quality for coffee it is necessary to examine the components which determine the positive aromatic characteristics typical of a specific coffee along with the components generated during the roasting process. The point is that while the flaws, as explained in the previous issue of Coffee Taster, come from a few chemical species, the positive elements are the result of the interaction of tens or hundreds of different molecules. Currently, the specialists are trying to identify the individual markers of quality or the simple connections between the elements transformed during the roasting process.
The chemical compounds that produce such distinguishing features are present in the raw material and they undergo major transformations during the roasting process which not only occasion significant transformation of the individual original compounds, but also combines them creating synergies and antagonisms which contribute to determining the final aroma of the beverage.
It is important to note what follows:
- the body is given by fats, macromolecules and colloids;
- the perceived acidity is given by the aliphatic volatile and non volatile acids, chlorogenic acids, phenol acids and inorganic acids;
- the bitterness comes from compounds such as caffeine, trigonelline and chlorogenic as well as chinic acids;
- the sweetness comes from the sugar compounds still present after the roasting process;
- the fruity and flowery notes typical of coffees from south America are given by aldehydes, ketones and alyphates.
Moreover, there are several other sets of compounds which contribute to the overall aroma, for instance the furnas – which give the caramel note, pyrazines – toasted note, tiazoli, pyrroles, phenols and thiophenes.
The ratios between such compounds have an impact on quality. For example, the ratio between 4-vinilguaiacol and 4-etilguaiacol, elements which – taken on their own – are characterised by markedly different aromatic notes, is responsible for distinguishing traits, in terms of aroma, of the Arabica and Robusta.
In collaboration with: E.Cossio, F.Battistutta