Hi again Andy,I asked a chef today.It is the heat apparently,not so much the lime juice. To prevent curdling add some starch to the yoghurt,a tablespoon of flour to each cupful of yoghurt is the ratio. Also, to help even more,instead of adding the cold yoghurt to the hot sauce,add a couple of spoons of the sauce to the yoghurt to warm it up and then stir and add back to the pan.This'll be more gentle!This makes me hungry....hope you get some success with this.Barb