Coffee Roasting machines do not make coffee sour, they make them sweet. There are 3 things that can make coffee sour.

● under-roasted coffee, especially new crop.
● Defect in the green called ferment that comes from the improper processing of the green. That aroma/taste runs anywhere from vinegar, to rotting fruit to baby diapers. It happens, even with the best supplier
● Brewing, if you leave coffee sitting around, especially if it’s in a heated container, it will turn sour.