whole wheat sourdough bread

I refreshed my still-kickin' sourdough starter to make this whole grain sourdough bread yesterday. In addition to the whole wheat flour, I added brown rice and oats to the dough, which resulted in a moist and very flavorful bread. My only complaint was that where some of the brown rice made contact with the hot baking stone, those rice bits became very hard, so some mouthfuls of bread had a little painful surprise when you bit down. No idea why this happened, because I didn't have this problem with earlier loaves containing brown rice.