Of all the
processes involved with coffee, the quickest and most critical is
roasting. Roasting coffee is a terrible responsibility, because, in a few
minutes, beans that cost hundreds of people time, effort and money can be
completely ruined by ignorance or carelessness. Roasting coffee is an art,
and like all true art, it takes years of practice before one becomes a
master roaster; also, roasting is learned only by trial and error
experience, and the errors may ruin many beans.
reason that roasting is difficult is that virtually every batch of beans
is different from every other. In factories, a small sample of every
shipment is "batch" roasted to anticipate every potential problem that
could arise in a commercial-size roast of perhaps 114 kg/250 lb of beans. A
bright rather than a dull roast is desired, as dullness can indicate
over-drying or poor processing; also, a good quality sample of beans will
appear even, since a variety of colors, particularly "pales", among the
coffee beans can indicate immature picking, poor sorting of cherries, and
varying degrees of fermentation and drying on the plantation. Misshapen
beans, broken beans, or simply an overly wide variety in bean sizes
constitutes a "ragged" roast, as different-sized beans roast to different
colors in the same roast.
changes that occur to beans during roasting are many; the obvious changes
are that the beans get bigger, gaining up to a third more of their former
"green" size; this is because the decomposing carbohydrates create carbon
dioxide, which literally causes the cells of the bean to expand.
Meanwhile, most of the moisture remaining in the green beans after the
plantation de-pulping, drying, storing and shipping, will be evaporated by
the heat of roasting, and the beans will thus lose weight. Although
moisture content can account for up to 23 per cent of green bean density,
dehydration during roasting is usually kept to a maximum of about 15 per
cent of the beans' weight, lest they become tasteless, brittle objects
that reduce to powder at the first touch of a grinder's blade. The other
very obvious physical change is that beans change color during roasting.