Some Exceptions: Sumatras often look like they are in the City roast while in fact they are into 2nd Crack. On the other hand, there is an occasional coffee that over-represents the degree of roast, that looks darker than it truly is, such as some Kenyas and St. Helena (and some would say that dry-processed Brazils are in the category too). Dry-processed "natural" coffees do not roast to an even color, so it is hard to judge the median color of the batch to determine the degree of roast. And none of these factors necessarily have a bearing on the quality of a raw coffee: quality is determined in the cup!
Degrees of Roast and Photos courtesy of SweetMarias
1. Green unroasted coffee - If you are holding an unroasted bean, you either are holding a berry right off of the plant, or see what has been processed out of the plant: the green coffee bean. The bean comes in many varieties, but regardless of origin, size, or shape, they will all have a tint of green to them.
2. Starting to pale - A recently heat-exposed coffee bean will look more pale in color.
5. Light Brown/Cinnamon stage. First crack is drawing near at this point. Some bean expansion is visible as the central crack in the coffee has opened slightly. This allows the coffee to release some of the silverskin in the form of chaff that has been attached to the bean in the folds of the crack
6. Brown Stage - right at the door of first crack. In a short time the coffee has browned considerably, which is partly due to browning reactions from sugars, but largely due to another browning reaction called the Maillard Reaction (which also is responsible for browning of cooked beef!)
7. City Roast. As the bean heats up, it comes to the point where heat must escape from the inside of the bean. This makes a crack sound known simply as "the first crack". This sound can be similar to popcorn pops, in distinction to the sound of the Second Crack, which has a shallower sound, more like a snap. Caramelization occurs in the bean browning it further. Some roasts are pulled here, but it is more rare than darker roasts.
8. City+ Roast. The stage between the first and second crack. The bean heats back up following the first crack. Further caramelization occurs. 
9. Full City Roast. At this point, the coffee is on the verge of 2nd crack. first crack is the physical expansion of the coffee seed as water and carbon dioxide split and CO-2 outgassing occurs. Second Crack is the physical fracturing of the cellular matrix of the coffee. This is more subtle sound, one of a rolling snap or pop (similar to Rice Crispies(R) snapping, crackling, and popping in milk).
13. Italian/Spanish/Fully Carbonized Roast. The bean has nothing left to do but burn up. It is completely black, fully carbonized with little trace of flavors remaining. The second crack is complete.
Why Roast Coffee?
HOME ROASTING TIPS from Imbibe Magazine
1) Never walk away from a roaster that’s roasting.
No matter how tempting it is to step away for a moment, DON'T. Just like a batch of cookies, coffee can get away from you quickly. It's better to hover nearby. And remember, a safe roaster is one that's unplugged when not in use.
2) Don’t smoke yourself out.
All roasters emit a certain amount of smoke (some more than others), so always be sure to roast your coffee in a well-ventilated area, such as a porch or garage.
3) Size matters.
The larger the batch, the more it will continue to coast into a darker color as you begin the cooling process, so plan for that. A smaller batch will roast faster than a larger one. A faster roast tends to be a little brighter, while a slower roast tends to have more body. Also, all roasting produces some smoke, but large batches generate more smoke than smaller batches.
4) Time is part of the recipe.
Once roasted, pay attention to how long the coffee needs to rest before it tastes best to you. It might seem contrary to the idea of freshness, but if your coffee begins to sing at four, five, even six days out, then plan ahead for that. Some coffees will be perfect the day after roasting, while some espresso blends find greatness more than a week later.
5) Try blending a coffee to itself.
Here's some homework: Roast a few batches of the same coffee—dark, light, and in between. Note how they taste different on their own, then start mixing the batches together. Some combinations will go muddy; others will become vibrant. You can have a lot of fun with this, and knowing one particular coffee well will give you greater insight if you do decide to introduce other beans into your blend.
Coffee Roasting Methods
Hot Air Corn Popper from Lucid Cafe
Gas Oven from Lucid Cafe
Popper Roasting (with photos) from Coffee Geek
Photo Guide to Coffee Roasting Using Popcorn Popper
Step by Step Guide Using Coffee Roaster from About.com
Guidelines For All Roasting Methods
The most important consideration when roasting your own coffee is knowing when to stop the roast. As you become more experienced you will be able to stop the roast with more precision while relying on the following methods:
Fresh roasted coffee
*Color: start with some roasted coffee that is roasted to the style you prefer. Use these beans as a guide, or refer to the photos shown above.
*Temperature: use a candy or deep fry thermometer to measure the temperature of the beans while roasting. If using a roasting machine, this method is not necessary.
*Smell: when the beans are nearly done the smell will change from a wet grassy vegetable smell to a coffee smell. As you gain experience, your sense of smell will become more refined.
*Sound: Once the beans get hot enough, they start to crackle as the water in the coffee turns to steam and is forced out. There are two distinct stages of cracking, commonly referred to first and second crack.
*Time: All other factors being equal, such as type and weight of the beans and the roasting temperature, you can duplicate previous efforts by timing the duration of the roast and recording this information for each type of green coffee you roast. This method is especially useful when roasting coffee in an oven or with a coffee roasting appliance.
Cooling The Beans And Removing Chaff:
As soon as a batch of coffee is done roasting, it should be cooled as quickly as possible. The coffee beans will continue roasting from residual internal heat even after the heat source is removed. To speed the cooling process if roasting with an oven, stovetop, or campfire method, dump the hot beans into a colander immediately after removing from the heat source. If you have a large quantity of beans, using 2 colanders is even more efficient. Pour the beans back and forth between the 2 colanders slowly. If you do this outside and there is a slight wind, you can effectively remove the chaff this way as well. It is not necessary to remove every bit of chaff as it will not affect the flavor in small quantities.
Venting The Roasting Smoke:
Roasting coffee produces a bit of smoke, and this will have to be vented if you roast coffee indoors. A stovetop exhaust fan is typically adequate to vent smoke from most roasting efforts unless a large quantity of coffee is roasted very dark (the darker the roast, the more smoke is produced). In the absence of an exhaust fan, a portable fan in front of an open window will usually take care of the smoke.
Resting & Degassing: The 24 Hour Wait To Prime Time:
Fresh roasted coffee reaches its peak flavor and aroma about 24 hours after resting. A 24 hour rest period is not necessary but is preferred by many coffee lovers to allow the beans to fully develop their flavor and aroma. The rest period allows excess CO2 to dissapate and permits the coffee bean chemistry to stabilize.
SOURCE : TalkAboutCoffee
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