I have been roasting my own coffee at home for about 15 years now. There are tricks to getting better coffee from a market, but their's won't be better than my own efforts.
And while I am probably going into way too much detail here than I need to, once you do this process, it becomes second nature fast.
I literally wrote this off the top of my head in the span of 15 minutes.
I tell people that it is the difference between listening to your favorite song on a crisp new CD versus listening to that same song on an AM radio station 1000 miles away on a rainy night with static.
Yes, I know MP3 is more common, but you can also make a low bitrate MP3 that sounds like crap. I need that comparison.
If great grandma could do this using a skillet over an open fire, you can do it too using a popcorn popper and a lot of ventilation.
You only need Green Coffee Beans, and a good heat source.
Oh and I strongly suggest you get Whole Bean coffee and grind it at home. Once a coffee has been roasted, you lose flavor due to exposure to air. Only grind what you need for today. Get a small grinder, you will thank me.
A little science first.
You need green coffee beans. Unroasted coffee is a little green. Olive Drab I would say but I won't be too particular with that definition. Green coffee is uncommon because most people would rather get their coffee roasted, ground, and from the market. To them I say BLEURGH!
Don't get me started on the Burnt Beans you get at the Drive Through. Mine is better and so can yours be.
It is a Natural product. Similar to Wine and Cheese, coffee grown at 'this' location will taste different than coffee grown at 'that' location. Some prefer Colombian, Brazilian, Ethiopian coffees. Coffee only grows in the tropics, and it's fussy about climate. Shade Grown because the plants will burn out or just not thrive if there is "too much" sun, it also prefers a higher altitude because the shrubs don't like it "too hot".
Picked, washed, and dried, the coffee beans are packed in large sacks and shipped "to you" wherever you are.
Personally I prefer coffee from a little region in Guatemala (Huehuetenango) for its natural sweetness, but I have been drinking some from Ethiopia (Yirgacheffe) lately and find its complexity interesting for a change.
Yes, you can roast Decaf Coffee this way, and that is why I describe things in terms of "Crack" stages instead of temperatures and colors. Decaf starts out darker and it is difficult to do that kind of coffee by eye. I typically drink Half-Caff on non workout days, saving the High Test for a High Energy day.
And, Yes, you can tell a difference too. It's not just me. Tastes of chocolate, bitter, smoke and a long list of other words that may or may not make sense to you now.
Furthermore, the method you roast the beans and how long will change the flavor greatly. Not long enough and it's "Too Light" and the flavors won't come out. Too long and you end up with those "burnt beans" I sneer at.
So how do you know?
There is a process your beans go through while they are being heated and stirred. Color will change from green to tan to brown and even black.
There are two distinct stages of "Crack" that the beans will go through. It will crackle as it roasts, then quiet down, then crackle again.
First Crack and Second Crack.
First Crack is obvious when you hit it. The Beans are quiet in the chamber. All the sudden you get a crackling sound. The beans are expanding and venting off gasses. The beans are fairly hard so they need to let go of the gas somehow and you hear many of them crack. Similar to popcorn, but not quite so vigorous
This First Crack is where I pay close attention. When the cracks slow to one per three seconds each, I tend to stop the roast. Pour them into a large bowl to cool.
There are stages you can go through and each will give you a different flavor. Right after First Crack, you will get a higher amount of caffeine, and a more complex taste. If you are used to a super dark coffee like a Latin Coffee or a French Roast, keep roasting until you get to Second Crack.
Second Crack I personally consider too dark, but that is my own preference. Some of the complexity is gone by now as the heat is baking away some of the caffeine. The more subtle flavors will wane and you get a more smoky flavor. We have all had a "Strong Coffee" before and this will be where many of us will consider what we want.
Just not me.
Oh and stop after Second Crack. The beans will end up burning, literally and turn black.
However you will develop your own preferences and you will most likely change over time. I used to go to the beginning of Second Crack, but now I stop at First Crack when the beans slow to every 3 seconds.
The Roaster? How do I get one?
I use a popcorn popper. No, seriously. In fact I have used the same West Bend Poppery II that I bought at a thrift store in 2008 or so. It looks ugly, beat up, and has been stained by countless roasts in the yard and in the stove hood that vents outside. We put that in when we redid the kitchen, saves a lot of grief.
Why that specific popcorn popper at the back of the box on my stove? The base of the popper has a metal cup. The air blows in from the sides. If it blows in from the bottom, it is the wrong kind. The sides are important because it will keep the beans moving around vigorously while you are roasting. If it didn't, in the five minutes or so that it takes to roast, it would be uneven and you may still have unroasted beans commingling with burned beans. Not fun.
Yes you can roast with a skillet. It takes a fair amount of skill to stir things up while you are roasting, I just prefer to let the popcorn popper do the job for me.
Plug it in, wait for first crack, dump into a metal bowl to allow things to cool. Reset the process and repeat.
Finally when can I drink?
Tomorrow. Give it a day. I say "Roast Today, Grind and Drink Tomorrow." I have a quart (Mason) jar that I use to store the coffee in once roasted. Allow the coffee to cool open to the air, and vent off Carbon Dioxide gas and humidity, and you'll have a mug of coffee that will blow away anything you ever experienced.
Fresh simply does not describe this.
If you have gotten this far remember It Just Is Not That Difficult. Like anything it needs preparation time. Get your beans, get your popcorn popper, and enjoy the process!