Two inventions have changed bread-making significantly: ovens and the action of yeasts. If you leave unbaked bread dough to stand, yeasts in the air cause fermentation: from thin doughs comes a kind of fermented drink, while thicker ones form a yeast dough that can be baked into light, tasty bread. Great Inventions goes on the trail of a staple food that is indispensable in Europe and North America, is around forty thousand years old and originates from northern Iraq, southern Italy and Israel.