Unicellular microorganisms belonging to the fungi (thallophyde = plants without roots and leaves), in spherical, oval, elongated to cylindrical or pointed form. They are between 5 and 14 thousandths of a millimetre in size (but significantly larger than bacteria). Most of them reproduce rapidly by cell sprouting, which is why they are also known as "sprout fungi". This process can take place up to 35 times.
The yeasts primarily need sugar as a source of energy, as well as some nutrients and trace elements, most of which are present in grape must. During fermentation, the sugars glucose (grape sugar) and fructose (fruit sugar) are converted into ethanol (alcohol) and carbon dioxide. The French scientist Louis Pasteur (1822-1895) made a great contribution to research into this complex process.
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