Making Cultured Buttermilk
I buy cultured buttermilk about every other week to make pancakes, mostly, but I also use it in cakes and biscuits. One week, I decided to replace what I used with regular milk. By the next weekend, I had a somewhat thinner version of what I had started with - but it was still very much buttermilky.
I did a little research online and found that to get the thick buttermilk, you had to let it culture at room temperature for about 24 hours after adding the milk. This thickening is called clabbering. The cultures get their best activity at about 70F, which is why it was thickening so slow in the fridge.
I was a little nervous about leaving dairy out for that long, but the website I was visiting, created by a chemist, assured me that it would work and that he had done it for years. So I poured a little buttermilk in a quart jar and filled the rest with 2% milk (because that is what I had - he recommends whole milk). I put the open jar in a crock pot, put the lid on the pot, and waited 24 hours.
And it did work!
What you should be seeing here is the thickened buttermilk pulling from the side of the glass. Can you see how thick it got? And it smells so good!