Mesquite bark has to be completely dry otherwise it gives a bitter tasteI do not remove the bark unless it is loose or if it has any type of fungus, rot, etc. I will remove the bark or just not use that piece at all.
I have performed tests using mesquite, pecan, oak and hickory with bark and without bark and I could not tell a difference in taste, tenderness or aesthetics.
I decided that it is one thing that I would not worry about in my own cooking.
I wonder if this where the general idea has come from. If wood is stored exposed to the weather I have noticed that it can be really damp between the bark and hard wood if well seasoned. Maybe bark hold moisture better in most woods and creates an off taste for some people.Mesquite bark has to be completely dry otherwise it gives a bitter taste