Am.  Jour.  Pharm.  | 
December,  1920.  j 
Yeast  Enzymes. 
917 
this  inversion  takes  place,  under  normal  conditions,  within  the  cell, 
since  it  was  found  that  invertase  cannot  pass  out  of  the  yeast  cell 
by  exosmosis. 
In  a  similar  manner,  maltose  which  is  also  a  di-saccharide, 
like  cane  sugar,  must  also  be  reduced  to  a  simpler  form  by  the  active 
agency  of  another  enzyme  before  fermentation  can  take  place.  To 
this  enzyme,  the  name  maltose  has  been  given,  and  while  its  pres- 
ence was  suggested  by  Bourguelot  as  long  ago  as  1866,  its  actual 
existence  in  yeast  was  only  demonstrated  by  Kmil  Fischer  and  others 
in  more  recent  years.  Under  normal  circumstances,  the  decompo- 
sition of  the  di-saccharide  maltose  into  the  monosaccharide  dextrose 
takes  place  within  the  yeast  cell.  As  the  result  of  these  investiga- 
tions it  has  been  proved  that  neither  a  biose,  triose  or  a  polysacchar- 
ide is  directly  fermentable.  All  have  to  be  reduced  to  the  simpler 
monosaccharide  or  hexose  form.  At  one  time  it  was  believed  that 
certain  moulds,  Monila  Candidad,  for  example,  was  able  to  ferment 
cane  sugar  without  preliminary  inversion,  but  later  investigation 
showed  that  this  organism  contained  an  invertase  which  affected 
the  h3^drolysis  of  cane  sugar  in  a  similar  manner  to  that  of  the  yeast 
cell.  In  addition  to  the  two  sugars,  cane  sugar  and  maltose,  brewers' 
wort  also  contains  a  number  of  complex  carbohydrates,  such  as 
dextrin  and  intermediate  bodies,  known  generally  as  malto-dextrins. 
These,  as  every  brewer  knows,  have  an  important  bearing  upon  the 
character  and  stability  of  beer,  and  have  much  to  do  with  the  con- 
dition and  life  which  characterizes  a  well-brewed  beer.  It  is  quite 
obvious  that  some  degradation  of  these  substances  takes  place  in 
cask,  and  fermentation  proceeds,  after  the  normal  or  primary  fer- 
mentation has.  been  completed,  and  this  is  due  to  the  fact  that 
certain  yeast  secrete  diastase,  and  are,  therefore,  capable  of  liy- 
drolyzing  the  complex  carbohydrates  slowly,  and  so  enabling 
a  gradual  but  steady  fermentation  to  takes  place.  Yeasts,  and  even 
the  ordinary  mixed  yeasts  of  the  brewery,  differ  in  their  capacity 
for  cask  fermentation,  hence,  in  a  perfect  yeast,  if  one  excludes  the 
use  of  foreign  yeasts,  which  do  not  readily  accommodate  themselves 
to  a  wort  of  beer,  one  requires  the  power  of  degrading  certain  com- 
plex carbohydrates,  such  as  the  so-called  malto-dextrins.  It  is  in 
this  respect  that  the  various  types  of  yeast  differ  so  much  in  respect 
to  attenuative  capacity.  That  Saccharomyces  (\'revisiac  is  ad- 
mirably suited  to  the  fermentation  of  the  brewers'  worts  is  plain 
from  a  consideration  of  the  enzymes  enumerated.    The  cell  contains 
