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Trivial Yeast Question

John BRATTY bratty at BCH.UMontreal.CA
Fri Nov 25 20:13:32 EST 1994

In article <3atjbm$s9u at mark.ucdavis.edu> ez005528 at rocky.ucdavis.edu
(Kevin Morano) writes:

   At the risk of starting a long conversation, I think that most ales are 
   brewed with Sacharromyces carlsbergensis, a close relative, and many 
   lagers (what Americans would call "normal" beer) are done with industrial 
   strains of cerevisiae. I maintain a couple ale strains on YPD plates in 
   lab and they behave very similarly but look a little bit different under 
   the scope. They are actually known in the brewing world as 
   "top fermenting" and "bottom fermenting", respectively (I think). Has 
   something to do with bouyant density during respirofermentative growth. 
   Maybe a vacuolar phenotype? (We try to relate everything to the vacuole, 
   if possible.)


   Kevin A. Morano
   Internet:kamorano at ucdavis.edu    
   Bitnet:kamorano at ucdavis   
   Section of Microbiology, University of California, Davis

Close, but not exactly right: S. cerevisiae is ale yeast.  It ferments
best at 20-25C and floats on top of the beer until fermentation is
complete at which point it flocculates and settles to the bottom.
S. carlsbergensis is lager yeast.  It ferments best at much lower
temperatures (5-10C), stays put on the bottom of the fermenting
vessel, and generates lower quantities of the flavourful and aromatic
esters that are more typical of ales.  If I am not mistaken (any
german speakers out there please correct me), the term "lager" derives
from a germanic root that refers to the longer period of time required
to ferment the beer.  Indeed the verb "to lager" (in english) means to
keep your beer cool for a period of time (several weeks) to age it.

There are also other strains/species of yeast used in brewing.  For
example, Bavarian wheat beer is normally brewed with another
Saccharomyces species while the Belgian lambics are brewed with "wild"
yeasts and often other microorganisms as well that live in the
breweries.  These variant yeast strains make a very big difference to
the beer that results.

Now, who can tell me what baker's yeast is?



John Bratty			bratty at bch.umontreal.ca
Departement de biochimie	
Universite de Montreal		(514) 343-6111, ext. 5165
Montreal, Canada		(514) 343-2210  (fax)
H3C 3J7

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