Coffee Roasting |
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Coffee Roasting |
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Back on the plantation the beans were sorted by size, density and
color, mostly so that the roasting time and temperature will have an
identical effect on every bean. Ideally coffee beans should be
roasted before they they are blended. But in big factories that is
not convenient, so a button is pressed and the greens beans in one
silo slide down a chute to join up with greens beans from several
other silos, all in the right weight proportions, and the whole lot
go into the roaster. The roasters are timed to the second, and the temperature strictly controlled. Conventional roasters work at between 200 oC - 240 oC, and the time can vary according to the condition of the beans and the color desired: beans that contain less moisture can burn if the time is not exactly right. Between eight and 14 minutes is normal. Towards the end of the roast the beans start to turn brown very quickly as their moisture content lessens and they lose weight; around 15 per cent is acceptable. At the same time they become about a third larger; and suddenly seem to burst, making little popping sounds, very like popcorn without the fluffy white "blossoms". Pyrolysis, complicated chemical change, is occurring within the 2000-plus substances which constitute a coffee bean. To a coffee lover, what really matters is that flavor and aroma are developing. The flavor of robusta beans benefits from a darker roast, but if they are blended with arabica beans before roasting, all will still be will: in the same roasting time, the drier, browner robusta will turn darker than the moisture-laden arabica. The darker the beans are roasted, the more the various kinds lose their distinctive flavors. This is particularly the case with arabicas, whose acidity lessens as the color deepens. Eventually the overall flavor is that of the roast itself, rather than the type of bean. In some cases this is desirable, as many a flaw can be disguised in a roast, but when an expensive arabica is roasted just that little bit too dark, its wonderful flavor and the high price that was paid for the beans are simply going up in smoke. As soon as the desired color has been attained, beans in a large commercial roaster will undergo "quenching", which is a quick showering of water over the beans. The water becomes an instant sizzle, but it serves its purpose, which is to stop the cooking process, cool the beans and prevent them from losing their aroma. There is no world standardization of terms indicating degree of roast, and although the names can be confusing, the solution is to drink enough coffee of different roasts to recognize what the color means in terms of personal preferences. All roasts are shades of light, medium and dark.
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