Bread-Bakers v110.n038.5

IMHO, kefir and yoghurt are equivalent from a breadmaking perspective 
and very similar to milk but with an acidic, sour flavour and 
slightly lower water content (*).  It's useful when making naan and 
similar flatbreads or when you want a soured slightly enriched dough.

Dan

(*) See http://www.nal.usda.gov/fnic/foodcomp/search/ for the details.