How to not burn the sugars in veggies when simmering in a dutch oven for a long time? I cooked a vegetable stew (onions, carrots, cabbage, potatoes) in a dutch oven on the stovetop for about 30-40 minutes on medium heat.  The food turned out fine, but there's a thick layer of black residue in the bottom of the dutch oven when I'm done cooking (which I am able to clean off).  Is this the burned sugars from within the veggies?  Is there a better way to cook for a long time with a dutch oven on a stovetop without leaving blackened residue on the bottom?
It sounds like either your heat is too high, or there is not enough liquid in your stew. If you can't reduce the flame, consider a heat diffuser.