Maybe 5 minutes. The warmer it is the faster it will work. You will be
able to notice some thickening. I find that the result is not as tart
as regular buttermilk, so I add a little more vinegar.

I do live in the mountainsat 7700 feet, but I don't that matters.

LaUna, in New Mexico

Jo Ann Schiefelbein wrote:
After mixing Tablespoon of Vinegar with milk to equal 1 cup...how long
should it "sit" at room temperature to become sour/buttermilk and safe
before using it for baking and etc.?
Jo Ann