Baking Without Yeast
Only the soft spongy dough produces delicious edible bread. This is what made people since Ancient Egypt use yeast in baking. They had observed that mixing flower meal with water, and leaving them on a hot day caused dough to expand before baking, and when it is baked they avoid getting the normal flat, hard cake. There would have been 'something' caused this change, and this 'something was yeast.
The word 'yeast' is originated from other words meaning boil, foam, or bubble.Yeast is a member of the plant kingdom which utilizes sugars to grow producing carbon dioxide. It is added to dough to produce carbon dioxide which penetrates it making it to expand and rise, and when baked it takes a spongy soft texture, with the yeast itself killed by heat.
Dough hosts yeast to cause a physical change in its structure, that is similar to that formed in Pumice.
How does Yeast Form Bubbles
A bubble is a foam in which gas is surrounded by a thin film of liquid. During mixing of dough, it entraps air- this air is composed mostly of Nitrogen and Oxygen - The yeast consumes oxygen during its aerobic respiration, leaving the nitrogen which is slightly soluble in water thus it retains its gaseous state, and this nitrogen gas is surrounded with a thin film of water forming bubbles.
As the yeast ferments, it produces carbon dioxide gas which is dissolved in water forming Carbonic acid, as the solution is saturated with carbon dioxide, then any formed gas is entrapped by the nitrogen bubbles already present, which then grow in size causing the dough to expand and rise. When the dough is baked, the gas is evaporated leaving holes inside the loaf, and the baked loaf is light and airy.
Yeast also plays a role in dough maturity/development, where the enzymes especially the proteolytic ones (that modify the gluten protein), although this is of more significance in bulk fermentation.
Yeast and Other Leaveners
It is understanding the role of yeast in leavening dough what made other leaveners possible.