Yesterday's article on grains did not cover one important bit of information on quinoa. Quinoa is nearly "birdproof" when grown as grain because the grain is coated with a bitter saponin. So it is necessary to rinse the grain thoroughly before cooking. Note that even when the grain is rinsed enough to remove the coating, it still tends to give off a slightly "bitter smell" in the first few minutes of cooking, though this does not impact the final wonderful texture and taste of the finished product.
Wikipedia recommends soaking in water for a few hours, draining, resoaking and draining, then cooking; or rinsing in a strainer or chesecloth with running water. All the quinoa I have bought in a store has only required some rinsing under running water, warm is best, for about 1 minute.
This includes bagged quinoa from Costco which was labeled as being prewashed. The Costco quinoa had a bitter odor while cooking and tasted mildly bitter when cooked. The Costco quinoa required about 20 seconds of rinsing to render the finished product palatable. So always rinse before cooking as modern business practice is generally to do the minimum required to make an ad claim.
Obviously quinoa that you grow yourself for the grain will require more rinsing than store bought grain.
The leaves of both quinoa and amaranth contain small amounts of oxalic acid, as does spinach. So do not eat a steady diet of these greens as it does interfere somewhat with the absorption of calcium by the body.