Yeast dough in the course of preparation increases in volume that noticeable with the naked eye – it rises in a pan and can even "escape" - to exceed the limit of the occupied capacity. Activity of barmy fungi is the reason of such rapid increase of volume of the test.
For preparation of the simplest test (for example, for bread making) the following components are necessary: flour, water, sugar, salt and yeast. All this carefully mixes up and in any capacity is located at several o'clock to the warm place: dough has to rise, otherwise bread will turn out rigid and tasteless. Here also work yeast, more precisely – barmy fungi begins. They, having got to conditions, favorable for their development, begin to breed. Fungi eat the starch which is contained in flour and sugar. At the same time carbon dioxide, alcohol and a number of organic compounds is emitted – there is a fermentation process. The formed vials of carbon dioxide create in the test of a cavity – the time loosening dough. The more this time, the test volume increases stronger, the quicker it rises. In the course of the reproduction, yeast eats some part of the test, but lump doesn't decrease due to increase of volume of yeast. The carbon dioxide concluded in the test seeks to escape outside, but doesn't allow to make it to it gluten – the substance which is formed at contact of starch with water. Viscous and strong gluten holds vials of carbon dioxide in the test, enveloping them from all directions. And dough grows more and more promptly and rises. However process of fermentation slows down at excess of carbon dioxide. Therefore dough is pressed down – carefully mix. At the same time surplus of carbon dioxide leaves the test, but it is enriched with oxygen that stimulates development of barmy fungi. At last, the risen dough is made in a heated oven or the furnace. In the hot atmosphere gluten dries up, its elasticity decreases. And each vial of carbon dioxide breaks off the cover and is released. And cavities (time) remain, and the baked bread turns out friable, porous, air – it what we love. Only yeast can provide "raising" of the test therefore products from a yeastless dough have absolutely other taste and an appearance, without having splendor and lightness.