Every kilogram of strained yogurt leaves about two kilograms of acid whey behind. It cannot go down the drain, it is hard to dry, and the 2013 "dark side of Greek yogurt" story was about it. Where it goes now, and what is changing.

One litre of milk, a spoon of live yogurt, a cloth and about 12 hours. The method, the temperatures that matter, what to do with the whey, and why your batch came out thin.

The two bacteria, the temperatures, the straining methods (cloth bag, separator, ultrafiltration), the 3-to-1 milk ratio and what happens to the whey.