Soak the black soybeans for at least 2 hours (better if for 8 hours or overnight)
Drain beans. Air dry them as good as possible - this step is very important when roasting in a pan*, but not so much if roasting in the oven.
Roast:A) In the oven - 50 minutes at 170ºC (340 ºF) , stirring a couple of times, the first after approximately 20 minutes.B) In a pan 40 minutes with low heat, stirring occasionally C) In the microwave 5 minutes at 600 W. Add 1 minute (for a couple of times) if needed.
The soybeans are ready when most are cracked and the inner side has a light brown color.
To make tea, use around 10 roasted soybeans per cup. Soak them in hot water for at least 5 minutes or cold brew them for 3 hours.
You can eat the soaked soybeans.
Notes
For more details on how to roast following each method, look at the instructions in the post above.*If your pan look burned after roasting, try this trick to get it clean easily and without rubbing.