As you know, quinoa is actually a seed and not a grain. This bitter natural coating comes from a substance called saponin. Saponin has a bitter flavor which discourages birds from eating it. You need to wash your quinoa really well in a fine mesh colander before cooking. We actually like to rub the quinoa between our fingers to clean it really good. If you wash quinoa well, it will be mild and nutty flavor and not have any bitterness.