The original buttermilk was the left overs from making butter. But most of what is now called buttermilk is a cultured product, much like yogurt and sour cream.

Many US groceries carry 'powdered cultured buttermilk', made from 'cultured nonfat milk'. I keep this on hand for use in pancakes and other baking. I have also found a full-fat version in the bulk section of a health-foods shop.

But I do not consider this a substitute for dried milk as a beverage, or for making cream sauces. It also tends to pickup moisture and harden into clumps, more so than Nido.

paulj