The markers of quality

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

The markers of non-quality

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.

Coffee is a drink that expresses most of its sensory characteristics in its smell and its aroma. The aroma is the sensory characteristic resulting from a combination of smells contributed by the chemical substances and by their intrinsic synergies and is the result of high-quality raw materials and of technological steps for the processing of the green matrix into roasted coffee which are thoroughly carried out. It is important to point out that the aromatic precursors are already present in the green bean which, exposed to roasting, develops new substances that contribute to the complexity with more than 800 volatile components found in a cup of coffee.
With regard to coffee, quality is based on two main aspects: the hygienic-sanitary quality, defined by regulations in force, and the sensory quality, defined by the aromatic and sensory profile.
Let us start with the hygienic-sanitary quality. For both the Arabica and Canephora (Robusta) varieties there are regulatory restrictions re the quantity of Ochratoxin A (OTA), secondary metabolite of moulds, mainly belonging to the Aspergillus type, present in both the green and the roasted coffee. Such restrictions are the result of proven negative effects on the consumer’s health. It is interesting to point out how the presence of OTA often goes hand in hand with a low sensory quality given that the attacks of moulds also bring about the formation of several secondary metabolites capable of influencing both the aroma and the taste of the finished product.
The contamination by moulds, coming from the raw material as well as from inadequate conditions during harvesting, processing, storage and transportation is among the factors which have the greatest impact on the sensory quality of a coffee. Components produced by moulds such as the 2-methylisoborneol, the geosmin and the 2,4,6-tricloanisole (TCA), for example, are responsible for major off-flavours: they create sensations of mouldy, earthy phenic, and rio flavour. It goes without saying that the absence of the said flaw-producing elements can be deemed as the first step towards impressive productions. Therefore, the above-mentioned elements can be seen as markers of non-quality to be determined, alongside the traditional parameters, during the qualitative assessment of a batch of green coffee.

In collaboration with: E.Cossio, F.Battistutta