I don't recall if the text says anything about it... I always drank it at room temperature. I drink most liquids at room temperature because it is said that's best for your body.
But I've read posts here where people keep it in the fridge, or warm it up like a tea.
I would imagine that, as with most foods, the more you change the temperature, the more it affects the vitamins, nutrients, etc.
But, you know, whatever works. :)
Also, the B&P shakes are not part of the Master Cleanse, though some people add them. For some people, it seems to be helpful, for others, it constipates them, so you might want to stick with herbal laxative tea and the salt water flushes.
If you haven't read the full text by Stanley Burroughs yet, there's a link to it online in a post below.