imponderable - a factor whose effects cannot be accurately assessed; "human behavior depends on many imponderables"

matter, substance - that which has mass and occupies space; "an atom is the smallest indivisible unit of matter"

baking powder - any of various powdered mixtures used in baking as a substitute for yeast

sourdough - a leaven of dough in which fermentation is active; used by pioneers for making bread

barm, yeast - a commercial leavening agent containing yeast cells; used to raise the dough in making bread and for fermenting beer or whiskey