First off the burner that is burning yellow needs to have the air plate adjusted to make it burn blue or turn down the gas. Secondly, you can keep the exterior of the dutch oven clean by coated it lightly with dawn detergent. Let it dry. Now when you use it again the soot will collect on the soap layer and be rinsed off when you wash the oven. We use our dutch ovens when we camp out and we maintain the exterior with the soap. Hope this helps.