My kefir is not sour. I use raw goat milk and I don't put a lid on the jar because the lady who sold me the grains told me to just cover the jar with a cloth. Because my apartment is a bit cool and it's winter, I keep the jar in the oven. I put the light on for a few hours and then turn it off for a few hours. I ferment them for at least 24 hours. Then I strain them in a plastic strainer to take out the grains, and then through cheesecloth to make quark cheese. (I just bought jelly bags to make that step a little easier.) Then since I started this whole process so that I could do the Budwig protocol, I blend the quark (strained kefir) with flaxseed oil and add some walnuts, berries and a bit of honey. It tastes divine.