Pita breads are also steam leavened, the big central hole comes from rolling from the center out. Other steam leavened recipes are pate a choux and popovers . Since the 1800s, when Louis Pasteur discovered how yeast works, scientists have isolated and reproduced different strains of yeast for yogurt and cheese, beer and wine as well as bread. Yeast is just not a product you can stow away and forget about until you need it next year. It is, after all, a living organism and if it's not alive at the time you need it, you won't get any use out of it.
Yeast is an ancient leavening, brewing, fermenting agent is a single celled microscopic fungus.
It's the carbon dioxide trapped by the dough that makes the air cells in the bread expand when heated, hence making it rise. The alcohol burns off during baking and flavors the bread. Packaged yeasts are finely ground and absorb moisture quickly to convert the flour's starches and sugar into carbon dioxide. There are several kinds available from the grocery store . Yeast will vary amongst brands and produce slightly different textures and flavor, all very successfully.