Brewing kefir with powdered cinnamon
Since no one else answered, I'll give you what I can.

Disclaimer: I never brewed with kefir grains. I brew beer, ciders, sometimes yogurt, and kefir started from commercial kefir.

I'm a big fan of cinnamon. So what I tried:


Filtration bags from brewers store simply fail to keep cinnamon dust in.
Filtration bags, extra fine cinnamon dust and gunk glue them so good that you can't really taste cinnamon in the final product.
Muslin bags as one of the above, depending on how thick and dense fabric is.
Dense metal mesh like the one you use on frying pan - tried to use it in couple of ways but nothing really worked.


Now, what worked? The only thing that worked for me was to first brew without cinnamon, then get my yeast out for reuse, and only then add cinnamon. After a day or two I decanted my brew leaving gunk on the bottom. Sadly this probably won't work for milk kefir. Sure won't work for yogurt, it's too thick. For juice-based drink it might work. It worked for me with ales and ciders fermented with yeast. Note: I needed to pitch fresh yeast with priming sugar to get any carbonation.