Why does quinoa taste bitter and how is saponin removed before selling?

The bitterness comes from saponin, a natural coating on the seed. Buyers and consumers want low saponin clean grain, so the seed has to be either dry polished or washed and dried to remove it. This is a real cost and a real step. Small farmers usually cannot do good saponin removal at home cheaply, so most sell raw clean grain to a processor who does the polishing, which means a lower price to you. If you want the better value addition price you need access to a dehuller or polisher and a proper drying setup, which only makes sense at FPO or cluster scale. Decide early whether you are selling raw grain to a processor or investing in processing, because that decides your real income.