A surprisingly large amount of things depend on yeast. Bread, alchohol, certain kinds of cheese- ect are all formed using yeast. Many species, including humans, live symbiotically with yeast inside their bodies.

One of my weirder near-future settings had a vaguely defined, maybe/maybe-not supernatural, apocalyptic event about twenty years ago called White Midnight. One of it's (many) wierdly specific effects is the selective mass extinction of yeast. I have plotted out some of the consequences of this- for example, in a world without alcohol, milkshakes spiked with small (or not so small) amounts of harder drugs became popular. Most bread is unleavened. Ect.

The question is, any other more weird unforeseen consequences of a world without yeast? For that mater, would the sudden vanishing of yeast just collapse the ecosystem outright and kill everyone?