Unicellular, to the mushrooms counting microorganisms (Thallophyde = plants without roots and leaves), in spherical, oval, oblong to cylindrical or pointed shape. The size is between 5 and 14 thousandths of a millimeter (but significantly larger than bacteria ). Most of them multiply rapidly by cell sprouting, which is why they are also called "sprout mushrooms". This process can take place up to 35 times. The yeast need above all sugar as an energy source, as well as some nutrient and trace elements most of which are in grape available. The yeasts play at the winemaking a crucial role. In the fermentation become the types of sugar glucose (Dextrose) and fructose (Fructose) in ethanol (Alcohol) and carbon dioxide converted. French scientist Louis Pasteur (1822-1895) earned special merit in researching this complex process.
The process is usually largely undermined anaerobic Conditions (that is, the absence of oxygen). Areobic conditions in the presence of oxygen are important before or at the start of fermentation, since the yeasts can only multiply in an oxygen-rich environment. The glucose is processed much faster, so in the residual sugar especially fructose present. As early as 1861, Louis Pasteur reported that yeast consumed much less sugar in an aerobic environment. With higher amounts of glucose in the grape must from about 100 mg / l can also under aerobic Conditions alcohol are formed. That is called Crabtree effect (or Pasteur effect). With small amounts of glucose, yeast inhale the sugar directly in the presence of oxygen, so it is not converted into alcohol.
The most important genus of yeast is "saccharomyces" (sugar mushrooms), of which there are over a hundred different types. The most common in the fermentation of Wine. beer and the type of sourdough involved is "cerevisiae" (cereals), in German meaning "brewer's yeast" or "baker's yeast". An older name is "Saccharomyces ellipsoideus" due to the mostly elliptical shape of these yeasts. The naming and classification of the different yeasts is extremely complicated. By DNA analysis many of the family relationships assumed up to now, and thus also the names, have turned out to be wrong. The taxonomic Due to these new findings, order will certainly change in one or the other point in the future.
There are over a dozen different...