I've prepared a quinoa salad at least half a dozen times. Up until these last two times the quinoa always came out fine. But this time some of the grains were hard in the center; you could even see that the center was white, not the cream color of the outside of the grains. The first time I noticed this I figured I undercooked the quinoa, so I made sure the cook it a bit longer this last time. It didn't seem to help. I don't want to end up with overcooked quinoa so I'm reluctant to increase the cooking time further. I'm wondering if this particular batch of quinoa might be old, or at least part of the batch is stale. Any ideas?