Sources generally agree the discovery of the powers of yeast was accidental."No one has yet managed to date the origins of beer with any precision, and it is probably an impossible task.Instead of placing the dough pieces for baking on the bottom or sole of the baking chamber, the Jews put the pieces on the sides.Being damp and sticky they remained in place intil they had dried out, when they fell to the bottom of the oven.When the heat was sufficient the embers were raked out and the pieces of dough placed in the hollows and covered over.
619-620) "It seems that the discovery of ale was stimulated by the process of bread-making.There is an alternate theory regarding the invention of brewing.Some historians believe it is possible that brewing began when the first cereal crops were domesticated.At some stage in the Neolithic era people had learned that if, instead of using ordinary grain, they used grain that had been sprouted and then dried, it made a bread that kept unusually well. The Egyptian process was to sprout the grain, dry it , crush it, mix it to a dough and partially bake it.The loaves were then broken up and put to soak in water, where they were allowed to ferment for about a day before the liquor was strained off and considered ready for drinking." ---Food in History, Reay Tannahill [Three Rivers Press: New York] 1988 (p.48) "Leavening, according to one theory, was discovered when some yeast spores--the air is full of them, especially in a bakehouse that is also a brewery--drifted onto a dough that had been set aside for a while before baking; the dough would rise, not very much, perhaps, but enough to make the bread lighter and more appetizing than usual, and afterwards, as so often in the ancient world, inquiring minds set about the task of reproducing deliberately a process that had been discovered by accident.