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Monday, November 3, 2008


Posted by coffee

It is the quickest and the most critical processes of producing the coffee. It is done in few minutes, and in those minutes determine the result of the coffee. Any careless practice of roasting the beans will ruined the thousands of people time effort and money. Roasting coffee is an art, it takes years of practice before mastering the coffee roasting, just like all true art. Learned only by trial and error experience, cost many beans, maybe too many.
The main reason that roasting is difficult is that virtually every batch of beans is different from every other. The physical 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 depulping, drying, storing, and shipping, will be evaporated by the heat of roasting, and will thus lose weight. Moisture content can account for up to 23 percent of green bean density, dehydration during roasting is usually kept to a maximum of about 15 percent 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 the beans change color during roasting.

The process
It is estimated that a coffee bean contains more than 2,000 chemical substances, which may be broken down or changed during roasting into hundreds of volatile aroma compounds. Thr most important roasting effect is that the flavor is developed through those complex changes caused by heat. Various acids, proteins, starches, sugar, vitamins, oils and caffeine are altered, some are enhanced and some are diminished, for certain case some substances are both developed and then burned away if the roasting time is extended.
A light roast is seldom used commercially, as it shows up all the flaws inherent in beans, many of which will disappear, or at least be hidden by other flavors, in a dark roast. The darker the roast, the more uniform all coffees taste, as a truly dark roast will overwhelm the taste buds, allowing them to perceive nothing of the coffee itself. A darker roast may sweeten some coffees, but only to a point, past a certain degree of roast all coffee becomes bitter. The darker the roast, the greater the loss of acidity, that most sought after quality. 
The roasting process begin with preheating the equipments for several minutes, which all vary in size and capacity, before adding the green beans to make all the surfaces uniformly hot. Many roasters are equipped with a revolving drum, often lined internally with curved metal strips which constantly toss the bean towards the centre of the drum. The beans must be kept moving if they are to roast evenly without burning. If the drum stops revolving while the heat is still on and the beans are hot, there is a danger of instant combustion within the drum.   


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