Effect of fermentation and roasting on the quality of coffee

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Impact of two different roasting processes on the content of pyridines in coffee originating from different regions.

How heat transfer occurs in coffee bean processing has a significant impact on the quality of the final product. In this context, the aim of a recent study, carried out by a group of international researchers (Gancarz et al., 2022), was to analyse the effects of the roasting process in a convection-conduction-radiation roaster with a heat exchanger on the aroma profile of coffee, and to compare them with those of a system without heat exchanger.

In particular, for the research, coffee beans from five different regions of the world were used, namely: Peru, Costa Rica, Ethiopia, Guatemala e Brazil. The product was analysed using SPME/GC-MS technique (i.e. Ultra gas chromatography coupled with mass spectrometer with solid phase microextraction) and an electronic nose. In general, the analyses revealed the dominance of azines, alcohols, aldehydes, hydrazides, and acids in the coffee aroma profile.

The high content of pyridine from the azine group was characteristic for the coffee roasting process without a heat exchanger. The authors argue that the presence of pyridine causes the development of bitter and unpleasant aromatic notes and is therefore a defect of the coffee roasting process. In summary, the study concludes that the use of a radiation heat exchanger allows for a better stability of the process temperature, resulting in an increase in the quality of the final product.

The influence of self-induced anaerobiosis coffee fermentation on the quality characteristics of coffee.

Although the microbiology associated with coffee processing has been widely investigated, few reports about self-induced anaerobiosis fermentation (SIAF) on the quality of the final product are available. Therefore, the aim of a recent study, carried out by a team of Brazilian researchers (Pereira et al., 2022), was to assess the impact of this technology on the microbial, chemical and sensorial profile of coffee beans grown under different environmental conditions, comparing it with that of a standard fermentation process.

In particular, in the SIAF method, coffee fermentation is conducted in closed, cylindrical high-density polyethylene bioreactors, taken to dry in suspended terraces until 11% moisture was reached. Standard fermentation, on the other hand, takes place outdoors. The test allowed the isolation of 380 microorganisms; belonging to mesophilic bacteria (149), lactic acid bacteria (147), and yeasts (84). Hanseniaspora uvarum, Lactiplantibacillus plantarum, Leuconostoc mesenteroides, and Weissella cibaria were identified in all samples. Some metabolites such as chlorogenic acid, sucrose, lactic acid, and trigonelline were identified in fermented coffees with nuclear magnetic resonance spectroscopy (NMR).

In conclusion, the authors argue that the SIAF fermentation process positively impacts microbial behavior of coffee, resulting in more intensified coffees with a fruity attribute compared to reference samples.

References: Gancarz et al., Molecules, 27, 2022, 1-12, T.S. Pereira et al., Food Microbiology, 103, 2022, 103962.