Kefir grains contain live active cultures, so I would advise not heating it.
Given this is the candida section of the board, I would recommend assuring that you have no yeast sensitivity before investing time/$ into making kefir. I used to live with some folks that did great on kefir and would extol its benefits. No matter how I ingested it, early/late, empty/full - I had a sensitive response to the yeasts/microbes that it is riddled with! Just a heads up...if there is no sensitivity then it should be extolled!
Sandor Katz offers an interesting perspective about why fermented food/drinks are more than substitutes for probiotics, but their superiority because of ever evolving microbiology.