Kitchenaid dishwasher - small pieces

Question

Kitchenaid dishwasher - small pieces of food are left on otherwise clean dishes. Water level comes to about 1 inch below heater coil. I ran it without dishes (or soap) and added about a quart of water so that level came to about 1/4 inch below heater and that's when I noticed food pieces on drain surfaces (nylon filter under bottom spray arm unit and circular plastic "trap" surrounding it). Spray arms holes are clear and water is hot.