In order to produce a nicely roasted bean it is very important that you start with high quality beans which have been selected with skill and dried correctly. You can spend all the money you want on a machine to coffee maker and machine to grind your brew, but if your beans aren't to your liking, neither will your coffee. Some coffee bean producers soak the beans in order to remove the unwanted fruit from the outside of the bean. Different densities of bean will float at different levels which makes it easier for them to separate them. Some other producers use a much more intensive and expensive dry process to separate the fruit.
Beans which have been dry processed will have a slightly less acidic taste. In wet beans they can be quite acidic. People do like a little acidic taste in their coffee, but not too much. What happens to beans as they heat up during roasting? When the beans are heated up, the beans start by absorbing heat. This changes the color of the green beans into a slightly yellow color.
At this stage the beans should smell a little like toast or possibly popcorn. When the beans reach around 170C sugars start to caramelize, this is made quicker by the pressure of moisture within the bean. This is why it's so important to choose beans which have the right moisture content, and ones which have been dried properly. When sugar is caramelized it's not as sweet.
When the beans get to around 205C the beans will start to swell up, they should double their original size and start to look brown. They will lose around 5% of the weight they had to start off with. Once the temperature gets to 220C they lose another 13% of their weight and start to release Carbon Dioxide.
If the temperature gets to 230C then the beans will become quite a dark brown color and have a glossy surface. Beans at this stage may crack for a second time. You must be careful at this stage as going much further could simply burn the beans and make them unsuitable for your coffee.
This can cause the beans to taste burnt and flavorless. You need to get the process right so that you end up with beans that have the right balance of flavors. When a coffee taster is referring to the body of the coffee they are not actually talking about the thickness of the liquid. It actually means how the coffee feels when they drink it. When the coffee is rubbed onto the roof of the mouth it feels a particular way. This varies depending on the fat content in the coffee, which is changed by the growing conditions and mostly by roasting.
If the roast is too light then it will be very acidic and bitter when you produce your final brew. If it's too dark a roast then it will be a much burnt coffee taste. You need to experiment in order to find a happy balance which suits your tastes.
Greg Hansward works normally for http://www.coffee-espresso-maker-tips.com , a web publication covering information on brewmaster coffee maker and grind and brew coffee. On his site you might come across his abstracts on brewmaster coffee maker and grind and brew coffee makers.