People have used yeast, undoubtedly one
of the earliest domesticated organisms, for controlled
fermentation of food and drink and for leavening in baking
throughout recorded history. Today, they are also used in a
variety of commercial fermentation and biomass conversion
processes. Their usefulness is based on their ability to
convert sugars and other carbon sources into ethanol in the
absence of air anaerobic, and into carbon dioxide and water
in the presence of air aerobic. Ethanol is a valuable
alternative to petroleum as a fuel and as a raw material for
the manufacturing of many important commercial chemicals.
Yeast is a tiny fungal microorganism. Most yeasts belong
to the order Saccharomyces, in the class of Ascomycetes.
Among the 350 known species of yeast the most familiar, Saccharomyces cereviseae,
is used in the fermentation process to produce the alcohol
in wine and beer and the carbon dioxide gas that causes
bread to rise.
Hieroglyphics suggest that the ancient Egyptian
civilizations were using living yeast and the process of
fermentation to rise their bread over 5000 years ago. Of course, they had
no idea what was responsible for this leavening process. The
development of the microscope and experiments on
fermentation using grapes done in the 1850's by Louis
Pasteur focusing on production of wine have allowed us today
to more clearly understand the biochemistry of this
invaluable process.
Links
The following websites contain valuable information for this achievement
task.
-
http://www.purefood.org/ge/devioddna.cfm
-
http://www.phys.ksu.edu/gene/a1.html
-
http://www.redstaryeast.net/ingred.htm
-
http://www.breadworldcanada.com/sciencehistory/science.asp
-
http://www.redstaryeast.net/sciencefree.html
-
http://www.phys.ksu.edu/gene/Mating4.html
-
http://www.phys.ksu.edu/gene/gloss.html
-
http://genome-www.stanford.edu/Saccharomyces/yeast_images.html
-
http://www.botany.utexas.edu/facstaff/facpages/mbrown/movies/
-
http://www.cells.de/cellseng/medienarchiv/archiv/bp1c1562d/1562_a62.htm
