Coffee: Volume 1: Chemistry
Language: English
Pages: 306
ISBN: 9401086931
Format: PDF / Kindle (mobi) / ePub
The term 'coffee' comprises not only the consumable beverage obtained by extracting roasted coffee with hot water, but also a whole range of intermediate products starting from the freshly harvested coffee cherries. Green coffee beans are, however, the main item of international trade (believed second in importance only to oiI), for processing into roasted coffee, instant coffee and other coffee products, prepared for local consumers. The scientific and technical study of coffee in its entirety therefore involves a wide range of scientific disciplines and practical skills. It is evident that green coffee is a natural product of great compositional complexity, and this is even more true for coffee products deriving from the roasting of coffee. The present volume on the chemistry of coffee seeks to provide the re ader with a full and detailed synopsis of present knowledge on the chemical aspects of green, roasted and instant coffee, in a way which has not been attempted before, that is, within the confines of a single volume solely devoted to the subject. Each chapter is directed towards a separate generic group of constituents known to be present, ranging individually over carbohydrate, nitrogenous and lipid components, not forgetting the important aroma components of roasted coffee, nor the water present and its significance, together with groups of other important components.
used for 'parchment' coffee forces it by means of a screw feed of reducing pitch into a confined space in which the parchment is broken by friction and removed by an air current. Hullers used for dry processed coffee can be of similar principle but the moving parts are fitted with projections which assist in tearing off the husks. Some types of huller require that the coffee be pre-graded for size to achieve suitable efficiency; also it is often the practice, in order to avoid damage to the
detriment to quality. Optimum extraction or 'yield' depends on the tempera ture of the extraction water and its rate of fiow through the ground coffee, and in practice the incoming water can be as high as 180 ac under high pressure. Since simple extraction of freshly ground coffee at this tempera ture would ruin its cup quality, the counter-current principle is operated. The six columns are 10aded in turn with fresh coffee and emptied of spent grounds, and the incoming hot water is introduced
that water wou1d boiI at temperatures below 100 DC, was a factor to be considered in devising suitable oven methods, but this is of doubtful importance. Oven drying on a small scale involves similar parameters to those investigated on a larger scale. The mechanism is, of course, complex, which may be further understood by reference to Karel 10 and Leniger and Beverloo. 11 For convective heating from hot air, the following general equation is relevant: dw de = k(P s - P.) ha = T (t s - ta)
with traces of other sugars such as sucrose, ribose and xylose. Glucose and fructose are also sometimes found, though the presence of the latter may well be due to the addition of instant chicory. The main data which have been published are compiled in Table 8, with results obtained using modern analytical techniques. The wide range of values observed for ali the sugars is a refiection of both ditTerences in samples studied and inherent ditTerences in the analytical methods. The TLC method 20
followed by extraction ofthe free amin o acids with aqueous alcohol. An alternative approach would involve using a more powerful, and hence efficient, solvent, but in this case the extract would have to be cleared to remove proteins and other macromolecules by precipitation, prior to separation of the amino acids. On roasting, free amino acids are severely degraded with the result that only traces are found in the roasted product and subsequent brews. l09 The amin o acids may be degraded by