When I put the Kidney Tea in the VitaMix I do get some white foam when its macerated, I think this is normal since it did that every time it was macerated but it goes away as soon as it settles.
Yes, each time you drink a cup of tea you are supposed to drink it heated. I never thought about adding a sweetener to the tea since I don't mind the taste. I'm not sure about that so I'll let someone else answer that for you but I'm thinking that if you did you'd have to use something natural like honey. I'm not sure how that would react with the healing properties of the tea.