When cooking your buckwheat you want the groats to be soft enough to enjoy, but not have a mushy texture. They should be firm and chewy. The best way to avoid mushy buckwheat is to buy quality groats. Those that you buy from Eastern European markets will be the best, and you can also purchase these brands online if you don't have a specialty grocery store close to you. Also, be sure to measure the water correctly, and don't add any additional water from rinsing the groats. Mushy buckwheat usually happens if there is too much water and the groats get overcooked. Keep an eye on them, and remove them from the heat as soon as you see that the water has been absorbed and you no longer hear a hissing sound from the pan.