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Chahan Yeretzian - Articles and news items

Progress on coffee roasting: A process control tool for a consisten roast degree – roast after roast

Issue 3 2012  •  4 July 2012  •  Chahan Yeretzian, Flurin Wieland & Alexia N. Gloess, Zurich University of Applied Science, Institute of Chemistry and Biological Chemistry and Marco Keller, Andreas Wetzel & Stefan Schenker, Bühler AG

A real-time automated process control tool for coffee roasting was developed to consistently and accurately achieve a targeted roast degree. It is based on timeresolved on-line monitoring of volatile organic compounds (VOC) in the off-gas of a drum roaster, using Proton-Transfer-Reaction Time-of-Flight Mass-Spectrometry (PTR-TOF-MS). These experiments provide a detailed, real-time picture of the evolution of the roasting process with the aim of controlling the process and consistently achieving a targeted roast degree.

The flavour of a freshly prepared cup of coffee is the final expression and perceptible result of a long chain of transformations which link the seed to the cup. These include agricultural factors such the variety of the plant, the chemistry of the soil, the weather and the alti – tude at which the coffee is grown. Combined with the way the cherries are picked, further processed and stored, a green bean is obtained that contains all the ingredients necessary for the later development of the typical coffee aroma. Yet, the green beans give no clue as to what they might become once roasted. They have neither the characteristic smell nor the taste of a good cup of coffee. To reveal the typical coffee flavour, coffee has to be roasted.

From a scientist’s point of view, roasting is the collection of a large number of heat induced time and temperature dependent physical and chemical transformations. It turns a hard, spongy to bite, green / grassy smelling bean into an intensely fragrant, brittle, and extractable dark brown bean.

The smell of coffee – an analytical perspective

Issue 4 2010  •  26 August 2010  •  Chahan Yeretzian, Alexia Glöss, Sergio Petrozzi, Lucio D’Ambrosio, Kaja Knöpfli-Lengweiler, Flurin Wieland, Andrea Fridolin Wild and Ruedi Anliker, Coffee Research Group, Zürich University of Applied Sciences

Within the last century, coffee has become one of the world’s most popular beverages and represents a major economic factor for many coffee-producing countries and a significant business sector in consuming countries. The success of this fascinating brew has been overwhelming and its future seems even more exciting1,2. The ever transforming landscape of coffee-shops and coffee-houses, the various trends and fads in the growing speciality coffee sector, the mounting awareness about origins, the steady innovations in the coffee machine sector and last but not least, the rising media-hype around the Barista-scene are all just the tip of the iceberg for a steadily growing coffee-lover community and an astonishingly recession-resistant industry.

Fuelled by high-level media and PR coverage and endorsed by celebrity ‘ambassadors’ such as George Clooney (for Nespresso coffees) and Roger Federer (for Jura coffee machines), this trend is here to stay and grow. Today, coffee is a brew full of passion, pleasure and plenty of myths.


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