Zurich University of Applied Science - Articles and news items

NIRS of chocolate and its chemometric analysis

Issue 6 2012  •  11 January 2013  •  Jürgen Stohner, Brenno Zucchetti, Fabian Deuber and Fabian Hobi, ZHAW Zurich University of Applied Sciences, ICBC Institute of Chemistry and Biological Chemistry and Bernhard Lukas and Manfred Suter, Max Felchlin AG

In today’s modern society, chocolate has been established as a premium lifestyle food product. Besides oil and coffee, cocoa is one of the most valuable commodities of global trade. About four per cent of cocoa beans traded on the world market originate from the noble criollo bean and are the basis of the so-called premium grand cru products (for more information, see www.icco.org). Due to fluctuating prices on the stock market and a current high price close to USD 2500 per tonne, chocolate manufacturers demand an efficient, reliable and speedy method for product and quality control. We report here on the analysis of cocoa with the help of near infrared (NIR) spectroscopy in the wavenumber range from about 4000 to 12000 cm-1 combined with chemometrics to determine the fat, protein, sugar and water content in chocolate base.

It is not just the flavour components of chocolate that largely influence the quality of chocolate – fat, protein, sugar and water also contribute to the desired mouth-feel, melting behaviour and flavour release. The quality of chocolate is significantly influenced by the content of the four constituents, namely fat, protein, sugar and water. It is, therefore, of great importance to develop and refine precise and reliable analytical methods to determine their amount in chocolate. The concentrations of these components are currently largely determined through costly analysis by external laboratories, which also delays the production process.

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.