We’ve found our own quality — and quantity — yogurt maker in a fish tank! All we did was buy a standard 50-watt tropical fish aquarium heater (for approximately $5) from a local variety store. We then cut a wooden 1-by-1-inch board to fit snugly in the “middle top” of our big kitchen canner, and fastened the water warmer securely to this cross brace. Next, we filled the canner with a 115-degree bath, and six pint jars of inoculated milk, plugged in the heater (we had to fiddle with the thermostat dial a little to figure out that perfect 110-to-115-degree setting), put the lid on the canner, covered the kettle with a thick blanket, and left the whole thing alone for a few hours.
The result? Our aquarium-heater-controlled incubation chamber kept the water bath and the growing culture at a constant temperature, and we got quarts of thick, creamy yogurt. And we’ve made “fishy yogurt” ever since, because our technique works every time.