Saccharomyces cerevisiae is the
scientific name of the yeast used in
bakery. This yeast is naturally present
in air. The size of each yeast is
between 6 and 10 microns.
(1 micron = 1 thousandth of mm)

Yeast (Saccharomyces cerevisiae)

In the absence of oxygen, glucose is degraded in ethyl alcohol (alcohol) and CO2 (carbon dioxide) by the yeast, it is the alcoholic fermentation:

CO2 fabricated by the yeast during baking is encapsulated in the paste.

The bread fills under the carbon dioxide pressure. You will notice that there is manufacture of ethyl alcohol.
Do this means that our breads are alcoholised? Not really because ethyl alcohol evaporates during baking.

The bread is made from flour and water but in these ingredients there is not glucose. Theoretically the previous chemical reaction cannot take place. However the baker adds a pinch of sugar.

In summary when you fabricate bread do not forget to add a pinch of sugar to your ingredients