Casein dewheying and dewatering screens


Hobman, P.G.; Elston, P.D.

New Zealand Journal of Dairy Science and Technology 11(2): 136-137

1976


A commercial-scale screen was designed at the request of a dairy company, to provide the flexi-bil:ty required to maintain efficient separation for a variety of casein curd types. The screen (Plate 1) incorporates a readily removable screen, the angle of which can be quickly and easily adjusted in the range 20° to 45°, thereby allowing for variations in curd characteristics. To prevent whey from spilling-over the front of the screen following adjustment of the screen angle. a reservoir extending beyond the front of the screen collects and subsequently discharges the whey (or wash waters). The screening material consists of 80-mesh (180 gym) stainless steel mesh, approximately 0.75 m × 1.20 in, and has a processing capacity of approximately 23 000 1/h of coagulum. When used for dewatering, however, the aperture size of the screen can be increased (to 300 micro-m for example), since only a minimum quantity of fines is normally produced during washing. Because of the increased aperture size, and since the quantity of liquid and solids (on a volume basis) decrease during washing, due to curd shrinkage, the capacity of the screens can be effectively doubled when used for dewatering.

136
Technical
Notes
New
Zealand
Journal
of
Dairy
Science
and
Technology
N.Z.
II
Dairy
Sci,
Technol.,
11,
136-137
(1976)
Casein
Dewheying
and
Dewatering
Screens
During
the
manufacture
of
casein
in
New
Zealand.
the
primary
separation
of
curd
and
whey
is
generally
performed
on
stationary.
inclined,
fi
ne
-mesh
screens,
fabricated
from
stain-
less
steel.
Similar
screens
arc
used
for
dewatering
curd
after
each
washing
stage'.
The
use
of
dewheying
screens
which
arc
poorly
designed
or
inefficiently
operated,
can
reduce
the
effectiveness
of
the
separation
and
may
influence
the
manufacturing
economics.
Such
a
reduction
can
be
caused
by:
(i)
Fine
curd
particles
passing
through
the
screen
with
the
whey.
This
may
be
due
to
the
production
of
an
excessively
fi
ne
curd
or
the
use
of
a
torn
screen.
(ii)
Whey
spilling
over
the
front
of
the
screen
with
the
curd.
This
may
occur
when
the
screen
is
blocked
or
overloaded
or
if
the
curd
characteristics
are
poor,
e.g.
'mushy
curd'.
Fines
which
are
lost
in
the
whey
represent
a
reduced
yield-
and
a
consequential
loss
of
revenue,
hence
their
recovery
is
important.
The
cost
of
recovering
excessive
quantities
of
fi
nes
from
the
whey,
however,
may
be
relatively
expensive.
A
more
satisfactory
approach,
there-
fore,
is
to
control
the
casein
manufacturing
oper-
ation.
so
that
the
production
of
fi
ne
curd
particles
is
avoided.
If
relatively
large
quantities
of
whey
enter
the
fi
rst
washing
vat
with
the
dewheyed
curd,
the
efficiency
of
the
washing
operaCon
is
decreased.
This
consequently
increases
both
the
volume
of
wash
water
required
for
the
operation
and
the
associated
water
-treatment
costs.
Furthermore.
there
is
an
increase
in
the
quantity
of
effluent
from
the
operation,
the
treatment
or
disposal
of
which
can
be
relatively
expensive.
If
the
whey
is
to
be
further
processed.
(e..t.
in
the
manufacture
of
lactalbumin),
then
a
loss
of
whey
in
the
wash
waters
represents
a
significant
decrease
in
the
potential
yield
of
the
whey
product
and
a
lower
return
for
this
product
(on
the
basis
of
milkfat
or
protein
in
the
milk).
Dewheying
studies
at
the
New
Zealand
Dairy
Research
Institute
using
pilot
scale,
stationary,
Plate
1.
Dcwheying
screens
in
operation.
inclined,
fine
-mesh
screens,
have
shown
the
dcwheying
efficiency
for
acidulated,
lactic
-acid
curd,
to
be
a
function
of
the
angle,
length
and
aperture
size
(in
the
range
180-350
p.m)
of
the
screen:
these
factors
being
in
decreasing
order
of
significance.
The
screens
have
also
been
found
to
operate
efficiently
in
the
dcwheying
and
de
-
watering
of
a
wide
range
of
casein
curd
types,
including
lactic
acid,
mineral
acid
and
rennet
caseins,
coprecipitates,
and
several
high
-moisture
or
'sticky'
curds,
which
are
inherently
difficult
to
dewhey
or
dewater.
Based
on
the
results
of
the
above
studies,
a
commercial
-scale
screen
was
designed
at
the
request
of
a
dairy
company,
to
provide
the
fl
exi-
bil:ty
required
to
maintain
efficient
separation
for
a
variety
of
casein
curd
types.
The
screen
(Plate
1)
incorporates
a
readily
removable
screen,
the
angle
of
which
can
be
quickly
and
easily
adjusted
in
the
range
20°
to
45°,
thereby
allowing
for
variations
in
curd
characteristics.
To
prevent
whey
from
spilling
-over
the
front
of
the
screen
following
adjustment
of
the
screen
angle.
a
reservoir
extending
beyond
the
front
of
New
Zealand
Journal
of
Dairy
Science
and
Technology
'37
the
screen
collects
and
subsequently
discharges
the
whey
(or
wash
waters).
The
screening
material
consists
of
80
-mesh
(180
gy
m)
stainless
steel
mesh,
approximately
0.75
m
x
1.20
in,
and
has
a
processing
capacity
of
approximately
23
000
1/h
of
coagulum.
When
used
for
dewater-
ing,
however,
the
aperture
size
of
the
screen
can
be
increased
(to
300
1
.1.m
for
example),
since
only
a
minimum
quantity
of
fi
nes
is
normally
pro-
duced
during
washing.
Because
of
the
increased
aperture
size,
and
since
the
quantity
of
liquid
and
solids
(on
a
volume
basis)
decrease
during
washing,
due
to
curd
shrinkage,
the
capacity
of
the
screens
can
be
effectively
doubled
when
used
for
dewatering.
Dewheying
screens
such
as
that
described
above,
have
been
operating
successfully
in
a
com-
mercial
lactic
acid
casein
factory
for
the
past
season
and,
combined
with
other
modifications
in
the
design
and
operation
of
the
manufacturing
equipment,
have
resulted
in
a
more
efficient
plant.
P.
G.
Hobman
P.
D.
Elston
N.Z.
Dairy
Research
Institute,
Palmerston
North,
New
Zealand
1.
King.
D.
W.
(1970).
N.Z.
11
Dairy
Sci.
Technol.,
5,
100.
2.
Roeper,
J.
(1973).
New
Zealand
Dairy
Research
Institute
45th
Annual
Report,
88.