91C-30 |
Evolution of carbon dioxide during roasting of coffee beans |
R. GEIGER1, R. Perren, and F. E. Escher. (1) Institute of Food Science, Swiss Federal Institute of Technology (ETH) Zurich, ETH-Zentrum, Zurich, CH-8092, Switzerland Roasting of coffee beans is a traditional thermal process, which is still designed and operated on an empirical base. Formation of aroma and of color compounds and changes in microstructure are the result of complex chemical reactions. Thereby, large quantities of carbon dioxide are formed and entrapped in the roasted coffee bean. The release of carbon dioxide during the subsequent storage causes flavor and requires special packaging techniques. In the present investigation the influence of various roasting parameters on the formation of carbon dioxide during roasting and the subsequent rate of release was studied. Batches of 100 g coffee beans were roasted in a fluidized bed hot air roaster at high temperature short time (HTST, 260 °C, 2.8 min) and low temperature long time (LTLT, 220 °C, 12 min) conditions. Evolution of carbon dioxide was monitored in the exhaust air by a LI-800 GasHound Analyzer and related to bean core temperature, moisture content, color development, volume increase and roast loss. Gas released during storage was followed by recording headspace pressure of closed containers. The rate of gas formation is strongly dependent on the absolute value and the rate increase of bean core temperature. LTLT roasting leads to higher amounts of carbon dioxide than HTST roasting. But HTST roasted beans showed a higher gas release during storage than LTLT roasted beans. Part of these differences can be explained by difference in bean microstructure. By combining these results with a judgement of flavor quality, selection of roasting conditions and of suitable packaging design can by placed on a more rational basis.
Session 91C, Food Engineering: Food process engineering
|