Bakers know two ways of getting dough to rise :
the first one, only for biscuits and cakes, is the use of a chemical powder which makes dough expand as soon as it is put into the oven ; the second one, for bread and Viennese pastry, is the use of natural living yeast which requires fermentation before it is put into the oven in order for the dough to develop.
The use of chemical powder may seem more simple and convenient, but its use is not appropriate for bread making. On the one hand, carbon dioxide is not produced in sufficient quantity to obtain a light and alveolated bread texture and, on the other hand, only a fermentation agent like yeast can give bread its organoleptic quality.
Bread is symbolical food which, in spite of its various compositions, is appreciated worldwide thanks to a special manufacturing process : fermentation.
	Between 1857 and 1863 Louis Pasteur demonstrated the role of yeast as a micro-organism responsible for fermentation. " All yeast which ferment bread, beer, wine and cider correspond to microscopic living cells of a microscopic fungus, Saccharomyces cerevisiae. Many varieties of Saccharomyces cerevisiae exist in nature and they are more or less suitable for the various types of fermentation".