Make no mistake about it, roasting your own coffee beans is not inexpensive. The beans themselves are quite expensive and can easily go beyond $10 per pound. If you buy a commercial home roaster, it can set you back around $200 or more. Those are very nice and allow temperature and time control. Some even take away the dust, chaff and smoke that accompanies coffee roasting.

My main contribution in this Instructable is a very simple one, put a chimney on a popcorn popper to make roasting easier. There are any number of YouTube videos that show how to use a popcorn popper to roast green coffee beans.

But, as long as I'm at it, I'll share my experiences with roasting green coffee beans.

Step 1: Materials and Equipment.

Coffee Beans

I bought green coffee beans from amazon.com. They are available at homeroastcoffee.com and other websites. It is incredible how many countries grow coffee and all of the variables that go with growing coffee--altitude,country latitude, how the green coffee beans are dried and washed, and genetics.
Basically, there are two varieties of coffee beans, Coffea arabica and Coffea robusta. Gourmet coffee is typically of the Coffea arabica variety and grocery-store coffee is of the Coffea robusta variety.
My specific first attempt to roast green coffee beans utilized Costa Rica Nectar beans. I bought three pounds so I would have enough to practice a lot.

Equipment

Popcorn popper (air popper) - mine is a very old one, but is still available in a more modern form. The temperature reaches about 360 degrees fahrenheit. Ask anyone, and they will say it is far too low. It would be better if it reached the upper 400 degree area. But, it works.
Power strip with electrical switch - my popper does not have a switch, so I use a power strip with a switch to allow for better on-off control.
Timer - I used the timer on my iPad for exact timing. Most smartphones have an app that can do timing as well. use whatever timer is handy.
Optional - Infrared thermometer. This is handy to see what kind of heat output I got, but it is not necessary

Step 2: The Air Popper

This is my contribution to the world of coffee roasting.

At first, I used the standard top on the popper, but the beans would tend to pop out and scatter on the floor. Then I used a wooden block to tilt the popper towards the back to keep the beans in as long as possible. That worked to some extent, but was not very handy. It definitely was not stable and would tip over easily.

I thought that if I could only extend the popping chamber, I would have a good home roaster. I looked around for something to extend it with and discovered that the Campbell Chunky soup can would do the trick. It is a tapered can and has a narrower top than bottom. The top fit into my popper exactly. So, I hurriedly ate a can of soup, washed it and then used a can opener to cut the lids of both ends. I used a plier to smooth the edges so I wouldn't get cut. This idea works like a charm.

Step 3: Roasting Green Coffee Beans

Here is where the rubber hits the road.

You need to decide how much roasting you want in your finished beans. It can vary from light roast to dark roast.

The popcorn popper roasting method only allows for manual timing and does not provide any kind of temperature control. Adding more or fewer beans can control roasting temperature somewhat, but that is a guessing game.

In any case, the bottom line for me is to use slightly less than 1/2 cup or about 120 cc of green, raw beans at a time. I settled for approximately 7 minutes of roasting time. That gave me a nice, dark roast, which is how I like my coffee. You can see in the pictures accompanying this step, what various roasts look like. I actually prefer an even darker roast in which the resin collects on the surface of the roasted bean and gives a shiny sheen to it.

Commercial, grocery store coffee is typically a medium roast for comparison.

Step 4: A Very Strong Hint

One thing you absolutely should do is to use this method outside.

The roasting process can give off a very strong odor--almost smoke, not quite. That raises complete havoc with any fire alarm, especially those connected to house wiring--the ones that cannot be turned off.

Also, the roasting process produces a LOT of chaff as the roasting proceeds. It's nice to do this on a breezy day and let the wind take care of the chaff--it is biodegradable, so you are not messing with the environment.

Step 5: Acknowledgement

I need to acknowledge my brother-in-law, Banlu, from Thailand. He taught me everything I know about coffee. He learned about coffee from the Doi Chang company which is located in Chiang Rai province in northern Thailand. He passed a lot of things that he learned on to me. So, anything that resembles the "academic" I learned from Banlu.