Thanks for the encouragement, everyone, especially to Katherine, who emailed me her secret whey substitute: plain yogurt. Yep, that’s it. I just had the best ginger ale of my life, and I made it myself. Ingredients: freshly peeled and chopped ginger root, a little bit of plain yogurt, distilled water. Seal tightly in a jar and wait two days, and strain out the yogurt curds and ginger.
It’s not carbonated, but it frims big-time!