Unfortunately I have just finished packing my coffee roaster away as I am retiring and moving in a couple of months and had roasted my green beans in readiness to last until after the move.
I have never used the oven as I felt I wouldn't be able to turn the beans enough and still keep the heat correct for optimal roasting.
Instead my son converted an old Sunbeam bread maker we found on a waste collection pile out front of someone's house we were passing over 10 years ago. Hopefully when I move I can post a pic of the converted roaster.
Since green coffee beans can keep many years just fine it gives me the option of buying many different kinds of bean and creating single or blends of flavors and aromas I prefer when they are on sale.
I only ever roast enough to see me through 10-12 weeks as after roasting quality quickly deteriorates. I only grind these amounts when I am ready to use them also for deterioration
reasons.
My son screwed a holding bracket to the side of the bread maker to hold a heat gun positioned directly onto the green beans. A fan is placed at the side of the bread maker and keeps going during the process. As the beans oscillate (turn) in the bread maker they get even heating and cooling happening. We listen for what is called 1st crack, then wait for 2nd crack when the beans are about ready - First Crack vs. Second Crack: Light/Medium roasts are defined by the first crack (popping sound), while Dark roasts reach the sharper, louder second crack.. FYI Roasting beans smell yuk! You will need a resealable foil pack to store the beans in for a few days while the gasses burn off then the beans can be stored as you would usually before use
There is a colour chart online that you can refer to as to how dark or light you want your beans to be. It also explains whether it will taste light, mellow, dark, and the bean overtones you can experiment to get, caramel, chocolate etc. I used a site called coffeesnobs.com.au for a lot of info on how to treat my beans but only ever bought a couple of times from them because their prices were too high, you can shop around for better bargains in your own country.
Key Roasting Color Stages
Green: Raw bean, room temperature.
Yellow/Yellow-Tan
Moisture loss stage, develops a toasty or bread-like smell.
Light Brown
Maillard reaction occurs, beans expand before first crack.
1st Crack
Light brown color,, pronounced acidity, "City" roast level.
Medium Roast
Medium brown color, balanced acidity and body.
Medium-Dark
Rich dark brown, oil begins to appear, "Full City".
Dark Roast
Dark brown/shiny black, oily, "Vienna/French" roast, low acidity.
Commonly Used Roast Categories
Light Roasts (Cinnamon/New England): Pale brown, high acidity, non-oily.
Medium Roasts (American/City): Balanced, brown, widely used for drip coffee.
Medium-Dark (Full City): Rich, dark brown with some surface oil.
Dark Roasts (Vienna/French/Italian): Shiny black/dark brown, bittersweet, smoky.
We had fun trying light to dark before choosing what would be our daily use one and our special occasion blend.
Great fun and well worth it once you get into the routine, compared to store prices and freshness. It is definitely more successful than an oven or any other method that isn't able to turn your beans while they are roasting.
Hopefully any of our talented permie DIYers on here can give it a go and post their pics.