Buttermilk refers to a range of fermented milk drinks where unrefrigerated fresh milk sours quickly. Buttermilk is produced from cow’s milk and has a characteristically sour taste caused by lactic acid bacteria.
It is very easy to find it at the grocery store. But, if you don’t happen to have when you are following a recipe, don’t worry, you may have what you need to not leave out this ingredient. In a liquid measuring cup, put a tablespoon of vinegar or lemon juice plus enough milk to measure an exact cup; let it sit for 5 – 10 minutes and ¡voilá!… your very own buttermilk.
See: Cornbread recipe