A recent stroll past the beverages section of my local natural foods store revealed five brands of kombucha in twenty-five plus flavors. In addition, there was kombucha soda pop—six or seven kinds. At the deli counter, I noticed kombucha on tap—eight flavors. Yet all I had to do to discover this latest health food craze was take a peek in our school’s glass recycling bin. Yep, mostly kombucha bottles.

For fifty years I’ve watched food fads rise and fall. First it was whole-wheat, which turned...