482 
Diastase  in  Malt  Extract. 
/  Am.  Jour.  Pharm. 
\       Sept.,  1889. 
ON  THE  ESTIMATION  OF  DIASTASE  IN  MALT 
EXTKACT. 
By  A.  Percy  Smith,  F.  C.  S. 
The  method  usually  recommended  for  the  estimation  of  diastase  in 
wort  or  extract  of  malt  depends  for  its  results  upon  the  time  taken  to 
saccharify  a  known  weight  of  starch,  the  end  of  the  reaction  being 
ascertained  by  the  failure  of  iodine  to  strike  a  blue  color. 
This  method  is,  in  my  opinion,  defective  and  inaccurate.  A  non- 
diastasic  extract  cannot  be  distinguished  from  one  which  contains  a 
small  quantity  only  of  the  ferment  without  the  employment  of  an 
elaborate  system,  using  starch  solutions  of  many  and  varying 
strengths.  The  end  reaction  is  not  sharp,  owing  to  the  starch  being 
reduced  to  a  minimum  and  to  the  solution  being  hot. 
A  more  convenient  and  exact  method,  although  not  claiming  scien- 
tific accuracy,  consists  in  estimating  the  reducing-power  of  the  extract 
on  Fehling's  solution  before  and  after  digestion  with  an  excess  of 
starch  during  a  period  of  four  hours  at  a  temperature  of  60°  C. 
The  starch  solution  I  employ  has  a  specific  gravity  of  about  1*02, 
and  is  made  by  dissolving  a  dessertspoonful  of  starch  in  about  two 
litres  of  water,  using  the  supernatant  fluid  after  deposition  has  taken 
place.    The  actual  strength  is  of  no  consequence. 
In  the  examination  of  thick  malt  extracts  I  make  a  1  per  cent, 
solution  in  distilled  water,  taking  care  not  to  heat  it  above  60°C.  in 
the  act  of  solution  ;  10  cc.  of  this  are  diluted  with  150  cc.  of  water 
and  boiled  in  a  dish,  while  the  Fehling  is  added  from  a  burette  held 
in  the  hand.  I  prefer  this  method  to  the  converse,  as  it  is  easier  to 
determine  the  presence  than  the  absence  of  a  blue  tint.  The  operation 
is  more  rapid,  and  one  avoids  the  discrepancy  caused  when  invert 
sugar  acts  upon  a  larger  quantity  of  copper  solution  than  it  is  able  to 
reduce. 
In  a  duplicate  experiment  in  which  the  copper  solution  is  added  all 
at  once,  instead  of  gradually,  it  will  be  found  that  \  cc.  less  is  re- 
quired. 
The  same  quantity  of  solution,  viz.  10  cc,  is  digested  with  25  cc. 
starch  solution  for  four  hours  at  60°  C,  when  it  is  diluted  with  150 
cc.  water  and  treated  as  above.  The  number  of  cc.  of  Fehling  used 
in  each  case  is  calculated  into  "  sugar  99  per  cent.,  and  their  difference 
into  "  increase  per  cent."    Less  than  four  hours'  digestion  with  starch 
