PROCESS  OF  CANNING  AND  PRE-
SERVING

Nature  of  the  Process. — Canning
or  preserving  is  a  process  of  killing,
by  means  of  heat,  the  germs  that
cause  decay  and  preventing  the  con-
tact of  other  germs  by  covering  the
produce  with  boiling  sirup  and  seal-
ing it  hermetically  so  as  to  exclude
the  air.  The  reason  that  boiling  is
necessary,  is  that  the  germs  of  decay
may  be  already  present  in  the  sub-
stance of  the  produce  itself.  Hence
it  must  be  boiled  until  the  heat  has
penetrated  every  part  and  eff'ectually
destroyed  the  germs.  And  the  rea-
son that  air  must  be  excluded  is  that


the  microscopic  germs  that  cause  pu-
trefaction float  in  the  air  in  very
large  numbers.  Hence  if  a  bubble  of
air  remains  among  the  fruit,  or  if
air  is  admitted  through  a  crevice  as
fine  as  a  needle  point  in  the  rubber
ring  or  metal  top  of  the  jar,  putre-
faction will  certainly  result.
Other  substances  such  as  clear  wa-
ter or  fruit  juices  exclude  the  air
as  well  as  sugar  sirup.  Sugar  is
added  partly  because  it  makes  the
product  more  palatable  and  nutri-
tious, and  partly  because  the  pres-
ence of  sugar  is  unfavorable  to  bac-
terial growth.  Hence  the  amount  of
sugar  to  be  added  to  a  given  quan-
tity of  fruit  may  be  varied  at  wiU.
