RESEARCHES  ON  ACETIC  FERMENTATION. 
343 
RESEARCHES  ON  ACETIC  FERMENTATION. 
By  M.  Pasteur. 
It  is  a  well  known  fact  that  wine,  beer,  and  cider  exposed  to 
the  air  turn  sour,  and  it  was  long  since  proved  that  this  phenom- 
enon was  due  to  the  alcohol  of  these  liquids  being  transformed 
into  acetic  acid ;  but  what  part  does  the  air  play  in  this  combus- 
tion, through  what  intermediary  state  of  transformation  does  the 
alcohol  pass  ? 
Acetic  fermentation  is  always  produced  by  the  exclusive  influ- 
ence of  an  organism — the  mycoderma  aceti — one  of  the  most  sim- 
ple vegetables,  consisting  essentially  of  frames  of  articulations 
slightly  compressed  towards  the  middle,  measuring  about  s^th 
of  a  millimetre  in  diameter,  and  double  that  in  length.  However 
much  charged  with  albuminoid  matter,  no  alcoholic  liquid  has 
ever  been  known  to  give  the  appearance  of  acetification  without 
the  presence  of  this  mycoderm.  On  the  contrary,  if  a  trace  of 
the  mycoderm  is  spread  on  the  surface  of  an  albuminoid  liquid, 
alcoholic  or  slightly  acid,  it  is  immediately  seen  to  develope,  ex- 
tend like  a  vail  over  the  surface,  and  by  a  correlative  action  the 
atmospheric  oxygen  in  contact  with  the  liquid  disappears  and 
the  alcohol  acetifies.  It  is  not  essential  for  the  liquid  to  contain 
albuminoid  matters  ;  provided  the  mycoderm  finds  there  besides 
the  alcohol  a  small  quantity  of  alkaline  and  earthy  phosphates,  it 
will  live  and  its  action  be  the  same  as  before  ;  and  this  identity 
proves  that  the  albuminoids  which  have  been  employed  were 
merely  nourishment  for  the  ferment,  and  not  the  ferment  itself. 
If  in  the  actual  process  of  vinegar  making,  acetification  takes 
place  without  the  previous  spreading  of  the  mycoderm,  it  must 
have  been  without  the  knowledge  of  the  experimenter ;  it  is  this 
organism  which  forms  the  gelatinous  mass  which  was  formerly, 
with  a  vague  idea  of  the  truth,  called  mother  of  vinegar ;  it  is 
this  which  by  spreading  over  large  surfaces  of  the  beechwood 
chips  used  in  the  German  process  produces  acetification.  By 
pouring  an  alcoholic  liquid  on  these  chips,  well  washed  and 
scoured,  and  thus  deprived  of  the  ferment,  no  trace  of  vinegar  is 
obtained  ;  but,  the  circumstances  being  favorable,  acetification  is 
produced  by  depositing  a  little  of  the  mycoderm  on  the  surface 
of  the  chips,  where  it  rapidly  developes. 
