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NEW  RESEARCHES  ON  ALCOHOLIC  FERMENTATION. 
NEW  RESEARCHES  ON  ALCOHOLIC  FERMENTATION. 
By  M.  L.  Pasteur. 
Contrary  to  the  opinion  generally  held,  I  am  able  to  affirm  that 
not  the  smallest  quantity  of  lactic  acid  is  found  in  alcoholic 
fermentation  ;  and  whenever  this  acid  is  found,  two  very  dis- 
tinct fermentations  are  accomplished  simultaneously.  Alco- 
holic fermentation  is  accompanied  by  lactic  acid  only  in  rare 
and  exceptional  circumstances,  and  when  peculiar  conditions, 
susceptible  of  being  reproduced  at  pleasure,  gave  rise  to  the 
yeast  which  I  have  made  known  as  lactic  yeast. 
This  new  yeast  being  formed  of  much  smaller  globules  than 
that  of  beer  yeast,  it  is  easy  to  ascertain  by  means  of  the  mi- 
croscope, if  there  is  a  mixture  of  the  two  yeasts,  and  thus  to 
anticipate  the  presence  or  absence  of  lactic  acid. 
One  question  naturally  presents  itself:  we  have  known,  from 
the  time  of  Lavoisier,  that,  in  alcoholic  fermentation,  the  liquor 
always  assumes  an  acid  reaction.  If  lactic  acid  is  found  excep- 
tionally by  the  means  which  I  have  just  pointed  out,  what  is  the 
cause  of  the  acidity  of  the  liquor  ? 
Numerous  experiments  have  enabled  me  to  ascertain  that  it  is 
to  succinic  acid  alone  that  the  acidity  of  the  liquor  in  alcoholic 
fermentation  is  due.  The  presence  of  this  acid  is  not  accident- 
al, but  constant,  and  with  the  exception  of  the  volatile  acids 
which  are  formed  in  infinitely  small  quantities,  it  may  be  said 
that  succinic  acid  is  the  only  normal  acid  of  alcoholic  fermenta- 
tion. In  whatever  conditions  I  have  hitherto  operated,  I  have 
found  succinic  acid  and  glycerin,  as  uniformly  as  carbonic  acid 
and  alcohol,  as  regards  their  existence  as  products  of  alcoholic 
fermentation. 
The  immediate  consequences  of  these  results  will  be  compre- 
hended by  every  one.  But  I  must  be  more  reserved  than  any  one 
in  their  discussion. — London  Chemist,  Oct.  1858,  from  Compter 
Mendus,  August  23  1  858. 
