Question: Why does roasting change a coffee seed?
About the article "Coffee", section "Roasting".

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The degree of roast has an effect upon coffee flavor and body.
Darker roasts are generally bolder because they have less fiber content and a more sugary flavor.
Lighter roasts have a more complex and therefore perceived stronger flavor from aromatic oils and acids otherwise destroyed by longer roasting times.
Roasting does not alter the amount of caffeine in the bean, but does give less caffeine when the beans are measured by volume because the beans expand during roasting.
A small amount of chaff is produced during roasting from the skin left on the seed after processing.
Chaff is usually removed from the seeds by air movement, though a small amount is added to dark roast coffees to soak up oils on the seeds. 
The next step in the process is the roasting of the green coffee.
Coffee is usually sold in a roasted state, and with rare exceptions all coffee is roasted before it is consumed.
It can be sold roasted by the supplier, or it can be home roasted.
The roasting process influences the taste of the beverage by changing the coffee seed both physically and chemically.
The seed decreases in weight as moisture is lost and increases in volume, causing it to become less dense.
The density of the seed also influences the strength of the coffee and requirements for packaging.
The actual roasting begins when the temperature inside the seed reaches approximately , though different varieties of seeds differ in moisture and density and therefore roast at different rates.
During roasting, caramelization occurs as intense heat breaks down starches, changing them to simple sugars that begin to brown, which alters the color of the seed.
Sucrose is rapidly lost during the roasting process and may disappear entirely in darker roasts.
During roasting, aromatic oils and acids weaken, changing the flavor; at , other oils start to develop.
One of these oils, caffeol, is created at about , which is largely responsible for coffee's aroma and flavor.
Roasting coffee transforms the chemical and physical properties of green coffee beans into roasted coffee products.
The roasting process is what produces the characteristic flavor of coffee by causing the green coffee beans to expand and to change in color, taste, smell, and density.
Unroasted beans contain similar acids, protein, and caffeine as those that have been roasted, but lack the taste.
Heat must be applied for the Maillard and other chemical reactions to occur.
As green coffee is more stable than roasted, the roasting process tends to take place close to where it will be consumed.
This reduces the time that roasted coffee spends in distribution, giving it a longer shelf life.
The vast majority of coffee is roasted commercially on a large scale, but some coffee drinkers roast coffee at home in order to have more control over the freshness and flavor profile of the beans. 
Home roasting is the process of roasting coffee from green coffee beans on a small scale for personal consumption.
Home roasting of coffee has been practiced for centuries, using simple methods such as roasting in cast iron skillets over a wood fire and hand-turning small steel drums on a kitchen stovetop.
Until the early 20th century it was more common to roast coffee at home than to buy pre-roasted coffee.
Following World War I commercial coffee roasting became prevalent and, combined with the distribution of instant coffee, home roasting decreased substantially.
In recent years there has been a revival in home roasting; what was originally a necessity has now become a hobby.
The attractions are four-fold: enjoying fresh, flavorful coffee; experimenting with various beans and roasting methods; perfecting the roasting process; and saving money.
These hobbyists are being catered to by various sources including coffee suppliers selling green coffee in small quantities and manufacturers making counter-top roasters. 
In modern times, "Kaldi Coffee" or "Kaldi's Coffee" is a popular name for coffee shops and coffee roasting companies around the world.