Nowadays
can
be
bought
at
the
store
,
but
until
yeast
was
readily
available
,
or
unless
people
lived
near
a
where
yeast
was
grown
on
the
fermented
mashes
used
in
making
beer
,
other
ways
were
used
to
make
.
Using
sourdough
was
one
of
them
.
Sourdough
may
be
the
of
all
breads
,
dating
as
far
back
as
4000
B
.
C
.
,
but
,
according
to
one
theory
,
it
was
unknown
in
America
(
which
is
famous
for
it
now
)
until
landed
with
a
sourdough
starter
in
the
hold
of
his
.
Sourdough
is
simply
a
self
-
perpetuating
yeast
,
made
by
combining
flour
,
sugar
and
water
and
leaving
it
to
.
Yeast
cells
,
always
present
in
the
(
and
flour
)
,
settle
on
this
broth
,
begin
to
,
and
set
the
starter
to
working
,
i
.
e
.
fermenting
.
The
bread
became
identified
with
America
because
of
the
Californian
and
Alaskan
"
sourdoughs
"
,
gold
prospectors
who
carried
sour
dough
starter
pots
strapped
to
their
packs
so
that
they
could
make
a
batch
of
whenever
they
felt
the
need
,
without
walking
50
kilometres
to
the
nearest
town
for
a
bit
of
.
Using
sourdough
,
however
,
was
risky
,
because
differing
such
as
temperature
and
light
affected
its
activity
.
Until
yeast
was
available
,
many
housewives
made
their
own
yeast
using
hops
,
potatoes
,
sugar
,
salt
,
flour
and
water
.
When
they
baked
,
the
housewives
would
mix
a
little
of
it
with
their
flour
and
other
ingredients
to
form
.
The
cowboy
cook
made
his
starter
by
mixing
up
some
flour
and
potato
water
in
a
keg
and
leaving
it
out
in
the
sun
to
.
Whenever
he
took
some
starter
to
use
,
he
returned
to
the
exactly
the
same
amount
of
flour
and
water
he
had
taken
out
.
New
Zealand
pioneer
women
made
yeast
-
based
(
rising
agents
)
in
several
ways
.
One
was
to
shake
up
some
ale
,
flour
,
sugar
and
water
in
a
bottle
.
The
contained
enough
yeast
for
this
mixture
to
work
.
Another
pioneer
used
extensively
in
New
Zealand
in
the
early
days
used
boiled
potatoes
,
flour
and
sugar
.
The
boiled
mixture
was
then
left
to
ferment
.
The
air
borne
cells
used
this
mixture
as
a
medium
to
grow
on
.
Yet
another
of
sour
dough
can
be
made
using
yoghurt
rather
than
yeast
.
In
this
case
,
the
bacteria
in
the
break
down
the
sugar
.
The
fermentation
produces
alcohol
and
carbon
dioxide
gas
.
Crear