910  1  iia^i  r^n^yma^.  |     December,  1920. 
SUMMARY. 
It  has  been  shown  that  Liebig's  process  for  HCN  properly  con- 
ducted gives  quite  satisfactory  results,  but  that  Guerin's  suggestion 
of  using  borax  solution  avoids  the  uncertainty  that  may  occur 
through  the  use  of  too  much  alkali.  Comparison  of  the  B.  P.  process 
with  that  of  the  U.  S.  P.  and  the  Codex  shows  that  the  B.  P.  appar- 
ently prescribes  too  little  KI.  However,  if  three  or  four  times 
more  KI  is  used  the  process  agrees  well  with  the  gravimetric  re- 
sults. It  seems  probable  that  any  defect  in  the  B.  P.  process  may 
be  due  to  an  insufficiency  of  iodide. 
YEAST  ENZYMES.* 
All  brewers  are  aware  that  considerable  differences  in  attenuative 
power  are  exhibited  by  various  brewery  yeasts,  but  it  is  not  so  well 
known  that  this  is  in  great  measure  due  to  the  nature  and  quantity 
of  the  enzymes  they  secrete.  According  to  our  contemporary 
the  (London)  Brewers'  Gazette,  investigations  by  many  scientific, 
observers  have  proved  the  truth  of  this  and  one  has  to  recognize 
the  remarkable  fact  that  ordinary  brewers'  yeast  used  very  day  is 
able  to  secrete  a  number  of  enzymes,  and  each  of  these  have  a  specific 
function  to  perform  in  carrying  out  the  complex  reactions  associated 
with  fermentation.  When  the  nature  of  these  reactions  is  fully 
understood  the  relationship  which  exists  between  attenuative  power 
and  enzyme  action  becomes  more  apparent.  The  first  enzyme  to 
be  discovered  in  yeast  was  invertase.  This  type  of  enzyme  has  the 
power  of  inverting  cane  sugar,  and  that  present  in  ordinary  worts 
is  quickly  converted  into  a  mixture  of  dextrose  and  levulose  before 
actual  fermentation  commences.  So  readily  does  this  yeast  enzyme 
act  that  a  well-known  process  for  making  invert  sugar  in  the  brewery 
is  based  upon  the  action  of  this  enzyme.  The  optimum  temperature 
for  effecting  this  process  is  about  130  degrees  F.;  but  lower  tem- 
peratures, such  as  those  within  the  range  of  ordinary  fermentation, 
are  sufficient  to  enable  this  enzyme  to  exercise  its  action  upon  any 
cane  sugar,  generally  present  in  small  amount,  which  may  find  its 
way  into  the  fermenting  vessel.  This  inversion  of  cane  sugar  into 
equal  proportions  of  dextrose  and  levulose  must  take  place,  before 
actual  fermentation,  caused  by  the  enzyme  zymase,  can  take  place. 
It  is  nearly  thirty  years  ago  since  J.  O' Sullivan  demonstrated  that 
*  From  Pure  Products,  October,  1920. 
