I use it exclusively as a buttermilk replacement. It works great! For
maximum shelf life, just store the container of powder in the
refrigerator. The brand I use is "Saco". I purchased mine at Cub
Foods/Waremart (in Oregon) in the baking section, but here's Saco's
phone #1-800-373-7226 (business hours central time).
Also, I've heard you can also substitute plain yogurt, or "soured milk"
for buttermilk. To make 1 cup soured milk, put 1 TB lemon juice or
vinegar in a 1 cup measuring cup; add milk (I use skim) to the 1 cup
mark.
Another option is to ask the manager at the grocery store if they would
special order it for you. I think most reputable grocery store chains
are willing to check into their customer's requested products.
The full name of the product is: "Cultured Buttermilk Blend for Cooking
and Baking" by Saco. I have a 12 ounce container.
Hope this helps!
Darby