That is exactly what I am doing. First ferment has kefir strained out, then that probiotic liquid goes to the wort. Been a fun journey, according to my hydrometer 2nd ferment can get as high as 7-8% ABV. Higher ABV has a negative effect when i bottle with respect to fiz. Still trying to work...
I got into brewing kefir beer by accident. When i started there was really not a whole lot out there on how to do it, recipes, etc. Going on almost a year of experimenting. Currently I am fermenting my Pumpkin Ales. I tried to embed a link to my blog i started to document all the variations...