Sarah,
I too am laying by a lot of baking soda. I too have spent enormous amounts of time pondering the absence of it. I found the answer in Carla Emory’s Encyclopedia of Country Living. It’s on page 220 in my book, under Acid-Base Leavenings. “In the real old days, they used to leaven with wood ash. Ashes are alkaline. If you add a teaspoon of ash to a mixture that contains an acid, such as real sour cream, buttermilk from slightly soured milk, or yogurt, then the two make bubbles. You have to work fast because the bubbles don’t last very long.”
My mother-in-law also confirmed this as the method used many years ago. – A.L.