I haven't yet tried it, but King Arthur Flour Co. lists dried buttermilk
twice in their catalog with slightly different comments:
Substitute for fresh buttermilk - 1/4 c. buttermilk powder + 1 c. water = 1
c. buttermilk.
In recipes calling for 1 c. buttermilk we recommend 1/4 c. buttermilk
powder (added with your other dry ingredients - it won't reconstitute) + 1
c. water. Our convenient-to-use, low-fat dried buttermilk is just 3.5% fat
dry weight, lower than store brands. In 1-pound bag.
1158 Dried Buttermilk, 1 lb., $3.50
They also list in the catalog 4209 Sour Cream/Buttermilk Starter, 1/4 lb.,
$3.00
Call toll-free, 1-800-827-6836. (Beware of contracting a bad case of the
"gimmes" if you get their catalog--lots and lots of appealing equipment and
ingredients.)
Their home page is <http://www.kingarthurflour.com>
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