'624  Preparation  of  Pressed  Yeast.  { ^'"Dec"'i8S2"''"'' 
12°  saccharometer.  On  analysis,  the  potato-mash  gave  O'l  per  cent, 
dissolved  nitrogen,  60  per  cent,  being  assimilable.  It  is  shown  that, 
contrary  to  the  opinion  usually  held,  this  solution  is  well  adapted  to 
the  growth  of  yeast. 
Delbriick  describes  the  employment  of  potatoes  in  the  cultivation  of 
pressed  yeast.  According  to  the  process  of  Schuster  and  Burow,  the 
potatoes  are  steamed,  water  being  previously  added.  Schuster  further 
uses  a  small  quantity  of  sulphuric  acid.  The  pressure  is  maintained 
at  a  moderate  degree.  Burow  recommends  to  introduce  into  the  steam- 
ers first  the  potatoes,  then  the  necessary  quantity  of  water,  and  finally 
the  reqinsite  quantity  of  bruised  maize.  The  effect  of  the  addition  of 
a  small  amount  of  sulphuric  acid  is  not  only  to  improve  the  color,  but 
to  prevent  the  formation  of  bacteria. 
Birner  recommends  the  use  of  asparagin  as  nutriment  for  the  yeast 
cell ;  for  this  purpose  leguminous  seeds  are  steamed  and  added  to  the 
mash. 
Schuster  proposes  to  prepare  pressed  yeast  and  s])irit  from  unbruised 
corn  without  the  application  of  steam  })ressure.  The  corn  is  digested 
with  sulphuric  acid  at  40°  (100  kilos,  corn,  660  cc.  pure  sulphuric 
acid,  and  200  liters  water).  After  the  expiration  of  48  to  60  hours 
the  material  is  brought  into  a  mashing  vat  and  ground  to  a  fine  pow- 
der, which  is  effected  with  great  ease.  The  saccharification  is  more 
rapid  and  complete. 
Hayduck  has  studied  the  influence  of  alcohol  on  the  development  of 
yeast.  Fusel  oil  was  found  to  retard  considerably  the  progress  of  the 
fermentation  of  yeast.  0*5  per  cent,  amyl  alcohol  in  a  10  per  cent, 
solution  of  sugar  impeded  its  progress,  while  2  j)er  cent,  completely 
prevented  the  fermentation.  Alcohol  arrests  the  fermentation  if  pres- 
ent to  the  extent  of  15  per  cent,  by  volume,  and  smaller  quantities 
retard  the  action.  The  fact  that  the  formation  of  yeast  is  usually 
completed  after  the  expiration  of  about  30  hours  is  explained  either  by 
the  c(msumption  of  an  ingredient  in  the  mash  indispensable  to  the 
development  of  yeast,  or  by  tlie  formation  of  a  fermentation  product 
which  prevents  the  further  progress  of  the  yeast.  It  was  also  found 
that  a  solution  of  potato-mash  containing  9*25  per  cent,  (by  volume)  of 
alcohol  showed  signs  of  fermentation  xifter  filtration  and  addition  of 
yeast,  but  did  not  develop  yeast.  After  the  removal  of  alcohol  from 
another  portion  of  the  filtrate  by  distillation,  adding  water  to  make  up 
the  solution  to  the  original  volume,  and  treatment  with  yeast,  a  further 
