Centrifugal dewatering of acid casein curd: Effect of casein manufacturing and centrifugation variables on curd compression in a laboratory centrifuge


Munro, P.A.; Van Til, H.J.

Biotechnology and Bioengineering 32(9): 1153-1157

1988


Data relevant to curd compression in a horizontal, solid bowl decanter centrifuge have been obtained by studying the dewatering of acid casein curd in a batch laboratory centrifuge. Analysis of curd compression under centrifugal force predicts a moisture content gradient in the dewatered curd from a maximum at the curd-liquid interface to a minimum at the centrifuge bowl wall. This moisture content gradient was also measured experimentally, and its practical implications are discussed. Increases in centrifugal force, centrifugation time, and centrifugation temperature all caused a marked decrease in dewatered curd moisture content, whereas increases in precipitation pH and maximum washing temperature caused a smaller decrease in dewatered curd moisture content.

Centrifugal
Dewatering
of
Acid
Casein
Curd:
Effect
of
Casein
Manufacturing
and
Centrifugation
Variables
on
Curd
Compression
in
a
Laboratory
Centrifuge
R
A.
Munro
and
H.
J.
Van
Til
Department
of
Food
Technology,
Massey
University,
Palmerston
North,
New
Zealand
Accepted
for
publication
November
20,
1987
Data
relevant
to
curd
compression
in
a
horizontal,
solid
bowl
decanter
centrifuge
have
been
obtained
by
study-
ing
the
dewatering
of
acid
casein
curd
in
a
batch
labora-
tory
centrifuge.
Analysis
of
curd
compression
under
centrifugal
force
predicts
a
moisture
content
gradient
in
the
dewatered
curd
from
a
maximum
at
the
curd
-liquid
interface
to
a
minimum
at
the
centrifuge
bowl
wall.
This
moisture
content
gradient
was
also
measured
experi-
mentally,
and
its
practical
implications
are
discussed.
Increases
in
centrifugal
force,
centrifugation
time,
and
centrifugation
temperature
all
caused
a
marked
de-
crease
in
dewatered
curd
moisture
content,
whereas
in-
creases
in
precipitation
pH
and
maximum
washing
temperature
caused
a
smaller
decrease
in
dewatered
curd
moisture
content.
INTRODUCTION
Centrifuges
are
widely
used
for
the
recovery
of
biologi-
cal
materials.
Their
use
for
the
recovery
of
protein precipi-
tates,'
for
the
dewatering
of
waste
water
sludges,'
and
for
cell
recovery
from
fermentation
broths'
has
been
reviewed
recently.
Most
research
work
on
centrifuge
performance
and
design
has
been
performed
by
equipment
manufactur-
ers
and
has
been
empirical
in
nature.
Relatively
little
fun-
damental
work
has
been
performed,
and
that
which
has
been
done
has
concentrated
on
liquid
clarification,
i.e.
par-
ticle
recovery.
However,
solid
deliquoring
is
equally
im-
portant
for
many
applications,
for
instance
where
the
solid
-liquid
separation
is
followed
by
a
washing
process
or
a
thermal
drying
operation.
For
porous,
compressible
bio-
logical
materials,
deliquored
solid
moisture
content
can
be
varied
greatly
by
altering
either
solid
preparation
variables
or
centrifugation
variables.
This
article
explores
the
effect
of
precipitate
manufacturing
and
centrifugation
conditions
on
the
centrifugal
compression
of
acid
casein
curd.
The
manufacturing
process
for
acid
casein
involves
isoelectric
precipitation
of
casein
from
skim
milk
followed
by
acidulation,
whey
separation,
multiple
stage
washing
with
water,
mechanical
dewatering
and
thermal
drying
of
the
resultant
precipitate.'
The
mechanical
dewatering
opera-
tion
has
been
carried
out
with
roller
presses,
belt
presses,
screw
presses,
and
decanter
centrifuges.
A
previous
labo-
ratory
study
on
casein
dewatering
focused
on
pressing
since
this
was
easiest
to
study
and
presses
were
the
pre-
dominant
industrial
dewatering
device.
4
A
laboratory
pres-
sure
cell
was
used
to
study
the
expression
of
water
from
washed
casein
curd
at
room
temperature.
The
most
signifi-
cant
finding
was
that
at
applied
pressures
greater
than
ca.
104
kPa
the
drainage
surface
of
the
curd
became
sealed
(restricting
water
flow
from
the
curd)
and
developed
a
translucent,
plasticlike
appearance.
Decanter
centrifuges
are
now
widely
used
for
dewheying
and
dewatering
casein
curd.'
Their
advantages
are
good
curd
dewatering,
good
control
of
curd
particle
size,
good
recovery
of
casein
fines,
and
relatively
hygienic
design.
Their
disadvantages
are
high
capital
costs,
high
repair
and
maintenance
costs,
high
noise
levels,
and
the
need
for
good
process
control.
De-
canter
centrifuges
were
included
in
a
comparative
study
of
three
pilotscale
casein
dewatering
machines.
6
This
paper
describes
experiments
on
casein
curd
compression
which
are
relevant
to
curd
dewatering
in
a
decanter
centrifuge.
CONCEPTUAL
ANALYSIS
OF
CURD
DEWATERING
IN
A
DECANTER
CENTRIFUGE
The
operating
principles
of
the
horizontal,
solid
-bowl
(decanter)
centrifuge
are
well
known.'
A
solid
-liquid
slurry
is
fed
into
the
central
portion
of
the
bowl
and
clari-
fied
liquid
and
dewatered
solid
leave
from
opposite
ends
of
the
bowl.
Conceptually
the
centrifuge
can
be
divided
into
three
zones.
At
the
cylindrical
end
of
the
bowl
fine
par-
ticles
are
centrifugally
settled
from
the
liquid
in
a
"liquid
clarification
zone."
In
the
center
of
the
bowl
there
is
a
"curd
compression
zone"
where
the
entering
particles
are
thrown
to
the
outside
of
the
bowl
and
are
compressed
by
centrifugal
force,
and
water
is
thus
squeezed
from
the
curd.
At
the
conical
end
of
the
bowl
further
liquid
drains
from
the
curd
as
it
is
conveyed
up
the
dry
beach
in
the
"curd
drainage
zone."
The
liquid
clarification
zone
may
be
Biotechnology
and
Bioengineering,
Vol.
32,
Pp.
1153-1157
(1988)
©
1988
John
Wiley
&
Sons,
Inc.
CCC
0006-3592/88/091153-05$04.00
analyzed
using
established
techniques
for
considering
the
settling
of
discrete
particles
from
a
dilute
slurry.
The
curd
drainage
zone
is
difficult
to
study
experimentally,
but
some
analysis
of
scroll
conveying
has
been
attempted.
2
This
article
considers
the
curd
compression
zone.
Curd
compression
is
much
more
important
for
porous,
com-
pressible
particles
such
as
casein
curd
than
for
the
incom-
pressible
particles
often
handled
in
decanter
centrifuges.
The
principles
of
centrifugal
compression
of
porous
protein
precipitates
are
similar
to
those
for
gravity
thicken-
ing
of
sewage
sludges,
which
have
been
well
studied.'
The
compressive
force
expressing
liquid
from
a
given
layer
of
particles
in
a
centrifugal
field
depends
on
the
density
dif-
ference
between
the
particle
matrix
or
solid
component
and
the
liquid,
and
also
on
the
mass
of
particles
above
that
layer
in
the
centrifuge.
There
is
thus
a
gradient
of
com-
pressive
force
in
the
settled
curd
from
zero
at
the
curd
liquor
interface
to
a
maximum
at
the
wall
of
the
centrifuge
bowl.
This
implies
that
there
should
be
a
gradient
in
mois-
ture
content
in
the
settled
curd
from
a
minimum
at
the
wall
of
the
centrifuge
bowl
to
a
maximum
at
the
curd
—liquor
in-
terface.
Such
gradients
in
moisture
content
have
been
demonstrated
experimentally
for
gravity
thickening
of
sewage
sludge.'
The
compressive
stress
useful
for
expressing
liquid
at
any
location
in
the
compressed
curd
layer is
given
by:
o
crr
P
(1)
Where
cr
T
is
the
compressive
stress
generated
by
the
mass
of
solids
above
this
layer
in
the
centrifuge
bowl
(Pa)
and
p
is
the
drag
force
exerted
on
the
particles
by
the
upward
flow
of
liquid
through
the
settled
solids
(Pa),
and
r
=
(1
-
pLIPs)w
2
rC
dx
(2)
where
p,,
p
s
are
densities
of
liquid
and
solid,
respectively
(kg/m
3
);
w
is
the
centrifuge
angular
velocity
(s
5;
r
is
the
centrifugal
radius
(m);
x
is
the
distance
below
the
curd
liquor
interface
(m);
and
C
is
the
solids
concentration
in
the
sedimented
curd
at
the
radial
position
x
(kg/m
3
).
The
first
term
in
eq.
2
is
the
stress
created
by
centrifugal
force
on
the
solid,
and
the
second
term
is
the
buoyancy
provided
by
the
liquid
in
the
sample.
Under
steady-state
conditions,
i.e.
after
long
centrifugation
times,
p
becomes
very
small
and
a
-
=
o
-
T
.
Equation
(2)
may
then
be
used
to
calculate
the
compressive
stress
forcing
liquid
from
the
curd,
and
to
predict
the
general
shape
of
the
moisture
content
profile
in
the
settled
curd
layer.
crr
EXPERIMENTAL
Preparation
of
Casein
Curd
Low
-heat
skim
milk
powder
(N.
Z.
Cooperative
Dairy
Company
Limited,
Hamilton,
New
Zealand)
was
dispersed
in
warm
distilled
water
to
produce
skim
milk
with
a
total
solids
content
of
9%
(w/w).
Acid
casein
curd
was
pre-
pared
by
heating
2
L
skim
milk
to
53°C,
stirring
vigor-
ously,
and
rapidly
adding
enough
0.3M
H
2
SO
4
to
obtain
the
desired
pH.
The
curd
—whey
suspension
was
stirred
slowly
at
53°C
for
10
min
(acidulation
period)
before
being
sepa-
rated
on
a
stainless
-steel
mesh
screen.
The
pH
of
the
whey
was
measured
after
cooling
to
20°C.
The
whey
pH
was
in
the
range
4.55-4.60
except
in
the
experiments
where
pre-
cipitation
pH
was
varied.
The
dewheyed
curd
was
nor-
mally
washed
three
times
at
temperatures
of
55,
75,
and
30°C,
but
the
maximum
wash
temperature
was
varied
in
one
series
of
experiments.
Each
wash
was
in
2
L
water
and
was
of
10
min
duration.
Centrifugation
Experiments
Centrifugation
experiments
were
performed
in
50
mL
round
-bottomed
tubes
in
a
Sorvall
RCSC
refrigerated
cen-
trifuge
(Sorvall
Products,
Wilmington,
DE).
Most
experi-
ments
used
an
SS
-34
angular
rotor.
Centrifugation
radius
at
the
bottom
of
the
tubes
was
107
mm.
However,
centrifu-
gal
force
values
were
calculated
using
a
radius
of
94.5
mm,
which
corresponded
approximately
to
the
mid
-point
of
the
curd
samples
at
the
beginning
of
centrifugation.
The
required
centrifugation
temperature
was
achieved
by
incu-
bating
a
curd
—water
slurry
in
a
water
bath
at
the
required
temperature.
For
temperatures
above
ambient
the
cen-
trifuge
was
run
at
medium
speed
until
frictional
heat
had
produced
the
desired
temperature.
The
centrifuge
was
maintained
at
the
required
temperature
by
the
refrigeration
circuit.
The
curd
was
drained
on
a
stainless
-steel
mesh
screen
(0.39
-mm
apertures),
and
20
g
was
placed
in
each
of
three
centrifuge
tubes.
A
sample
of
the
drained
curd
was
taken
for
moisture
content
determination.
After
centrifuga-
tion
the
surface
water
was
poured
from
each
centrifuge
tube,
and
all the
curd
from
each
tube
was
placed
in
a
mois-
ture
dish.
Mean
moisture
content
of
the
centrifuged
curd
sample
was
determined
by
oven
drying
for
18
h
at
105°C.
To
investigate
the
layering
of
curd
under
centrifugal
force
in
a
centrifuge
tube,
experiments
were
performed
as
above
but
with
a
HB-4
swing
-out
rotor.
Centrifugation
radius
at
the
bottom
of
the
tubes
was
146
mm,
and
centri-
fugal
force
values
were
calculated
using
an
average
cen-
trifugation
radius
of
120
mm.
After
centrifugation,
curd
layers
5
mm
thick
were
removed
from
the
centrifuge
tube
and
placed
in
separate
moisture
dishes
in
order
to
measure
the
moisture
content
profile
down
the
tube.
The
compara-
tive
mechanical
strength
of
various
curd
layers
was
deter-
mined
using
a
penetrometer
device.
A
3
-mm
-diameter
spherical
probe
was
attached
to
the
crosshead
of
an
Instron
Universal
Testing
Machine
(Instron
Ltd,
High
Wycombe,
Bucks.,
England).
The
probe
was
driven
axially
into
a
tube
of
centrifugally
compressed
casein
curd,
and
penetra-
tion
force
was
recorded
versus
penetration
distance.
1154
BIOTECHNOLOGY
AND
BIOENGINEERING,
VOL.
32,
OCTOBER
1988
RESULTS
AND
DISCUSSION
Layering
of
Curd
under
Centrifugal
Force
Results
for
curd
moisture
content
versus
depth
in
the
tube
(Fig.
1)
show
a
systematic
variation
from
drier
curd
at
the
bottom
of
the
tube
to
much
wetter
curd
near
the
liquid
interface.
Penetration
force
data
(Fig.
2)
also
indicate
lay-
ering
in
the
centrifuge
tube
with
more
compact
and
there-
fore
stronger
curd
at
the
bottom
of
the
tube.
It
was
also
observed
that
curd
plasticized
sooner
and
more
easily
at
the
bottom
of
the
tube.
Thus,
all
three
pieces
of
experi-
mental
evidence
indicate
drier,
more
compact
curd
at
the
bottom
of
the
centrifuge
tube.
Moisture
content
results
qualitatively
similar
to
these
were
reported
by
Sokolov
and
Sedov
9
for
the
centrifugation
of
cottage
cheese.
This
variation
in
curd
moisture
content
with
depth
in
the
tube
is
predicted
by
eq.
2.
As
a
first
approximation,
if
variations
in
r
and
C
with
depth
in
the
tube
are
neglected,
eq.
2
becomes:
=
(1
pdp
s
)w'rCx
(3)
i.e.
an
approximately
linear
increase
in
compressive
stress
with
depth
into
the
curd
layer.
Curves
for
dewatered
curd
moisture
content
versus
centrifugal
force
(Fig.
3)
or
versus
applied
pressure
for
press
dewatering
4
are
both
hyperbolic
shaped
with
a
vertical
asymptote
at
zero
pressure
and
a
horizontal
asymptote
at
55-58%
(w/w)
moisture
content.
This
predicts
the
general
shape
exhibited
in
Figure
1
for
curd
moisture
content
versus
depth
with
a
low
slope
at
the
bottom
of
the
tube
where
further
increases
in
pressure
cause
little
decrease
in
moisture
content.
Calculation
of
°
T
for
the
experiment
conducted
at
4000g
to
generate
Figure
1
indicates
a
compressive
stress
of
approximately
131
kPa
at
the
bottom
of
the
centrifuge
tube.
This
is
in
the
range
of
applied
pressures
where
increased
pressure
has
little
effect
on
curd
moisture
content.
4
Since
r
and
C
both
increase
70
0
cu
4—
6
0
0
LJ
CU
L.
rn
0
50
10
20
30
40
Curd
Height
(10
-3
m)
Figure
1.
Curd moisture
content
vs.
distance
from
the
bottom
of
the
centrifuge
tube
for
curd
centrifuged
for
20
min
at
30°C
and
(0)
2000g,
(L)
4000g,
and
6000g
(0).
y'
r
ee
.
,•
,Y
ee'
,Y
aJ
e
ee
.
L.)
/
C.—
O
Curd
Depth
05
1.0
Figure
2.
Force
exerted
on
the
penetrometer
probe
vs.
proportional
dis-
tance
from
the
curd
—water
interface
for
curd
centrifuged
for
20
min
at
30°C
and
(—)
1000g,
(--)
2000g,
(--)
4000g
and
(
)
6000g.
Total
distance
penetrated
ranged
from
29
mm
at
6000g
to
35
mm
at
1000g.
somewhat
as
one
passes
down
through
the
curd
layer,
o
-
,
will
increase
somewhat
more
rapidly
with
x
than
predicted
by
the
linear
relation
in
eq.
3.
Particle
segregation
in
the
centrifuge
tube
with
larger,
drier
particles
settling
first
to
the
bottom
and
small
ones
at
the
top
might
also
be
used
to
help
explain
the
results
in
Figure
1.
However,
this
is
unlikely
to
be
important
since
the
particles
are
large,
mainly
1-6
mm
in
diameter,
w
and
all
settle
by
gravity
well
before
they
are
put
into
the
cen-
trifuge.
The
major
practical
implication
of
the
variation
in
curd
moisture
content
between
curd
layers
is
that
cen-
trifuges
for
dewatering
compressible
materials
should
turn
the
solid
over
during
dewatering
so
that
the
damp
upper
layers
of
curd
are
also
effectively
dewatered.
The
decanter
centrifuge
achieves
turn
over
of
solid
by
using
a
screw
to
convey
the
curd.
In
all
subsequent
experiments
the
mean
moisture
content
of
the
dewatered
curd
was
determined
by
taking
all
the
curd
from
each
centrifuge
tube
and
drying
the
whole
sample.
Effect
of
Centrifugation
Variables
on
Moisture
Content
Dewatered
curd
moisture
content
decreased
with
in-
creasing
centrifugal
force
(Fig.
3).
However,
centrifugal
accelerations
above
6000g
have
relatively
little
effect
in
further
reducing
moisture
content.
Similar
results
were
re-
ported
for
press
dewatering
4
with
applied
pressures
above
100
kPa
having
virtually
no
effect
on
curd
dewatering.
The
cutoff
was
more
dramatic
for
press
dewatering
because
of
plasticization
of
curd
at
the
drainage
surface.
Dewatered
curd
moisture
content
decreased
with
in-
creasing
centrifugation
time
(Fig.
4),
producing
a
similar
curve
shape
to
that
versus
centrifugal
force
(Fig,
3).
Simi-
lar
results
were
presented
for
press
dewatering.
4
For
press
dewatering
it
was
possible
to
continuously
monitor
curd
MUNRO
AND
VAN
TIL:
CENTRIFUGAL
DEWATERING
OF
ACID
CASEIN
CURD
1155
80
0
0
0
0 0
0
cu
70
000
0 0 0
C
c._
60
\4C41
-1
"
I
'
°
-
--t
o
.________
SO
4
12
Centrifugal
Force
(10
3
g)
Figure
3.
Curd moisture
content
(0)
before
and
(•)
after
centrifugation
vs.
centrifugal
force
for
curd
centrifuged
for
20
min
at
30°C.
80
0 0 0
70
0000
0
0 0
-4-
0
60
tn
z
50
20
40
60
Time
(min)
Figure
4.
Curd
moisture
content
(0)
before
and
(0)
after
centrifugation
vs.
centrifugation
time
for
curd
centrifuged
at
30°C
and
4060g.
thickness
and
hence
curd
moisture
content.
The
decrease
in
curd
moisture
content
with
time
was
still
continuing
after
pressing
at
207
kPa
for
8
x
10
4
s.
From
the
results
in
Fig-
ures
3
and
4
centrifugation
conditions
of
4060g
for
20
min
were
chosen
for
the
rest
of
the
experimental
program.
Variations
in
sample
mass
had
relatively
little
effect
on
dewatered
curd
moisture
content
(Fig.
5).
Presumably
the
effect
of
greater
pressure
on
the
curd
with
a
larger
mass
of
curd
above
it
is
balanced
by
the
effect
of
the
longer
drainage
distance
for
moisture
to
travel
out
of
the
curd.
Adding
an
extra
15
g
water
to
a
centrifuge
tube
to
increase
the
hydrostatic
pressure
on
the
curd
had
no
effect
on
dewa-
tered
curd
moisture
content.
Increasing
centrifugation
temperature,
which
normally
equals
the
temperature
of
the
last
washing
stage
in
a
casein
plant,
caused
a
marked
decrease
in
curd
moisture
content
both
before
and
after
centrifugation
(Fig.
6).
The
upper
temperature
was
limited
to
40°C
by
the
method
of
tempera
-
80
70
C
60
0 0
0
0
0
CU
to
4-
0
z
50
0
10
20
30
Curd
Mass
(g)
Figure
5.
Curd moisture
content
(0)
before
and
(•)
after
centrifugation
vs.
mass
of
wet
curd
placed
in
the
centrifuge
tube
for
curd
centrifuged
for
20
min
at
30°C
and
4060g.
80
70
4_
0.)
-4-
0
60
a)
V)
50
15
30
Temperature
(
°
C)
45
Figure
6.
Curd moisture
content
(0)
before
and
(•)
after
centrifugation
vs.
centrifugation
temperature
for
curd
centrifuged
for
20
min
at
4060g.
ture
control
used.
No
curd
plasticization
was
observed
at
25°C
or
below,
moderate
plasticization
at
30
or
35
°
C
and
extensive
plasticization
at
40°C.
Increasing
wash
water
temperature
causes
substantial
shrinkage
of
casein
curd
particles
leading
to
lower
moisture
contents
after
screen
drainage."
2
This
curd
shrinkage
with
temperature
clearly
also
facilitates
further
moisture
removal
by
centrifugation.
The
data
for
moisture
content
after
centrifugation
in
Fig-
ure
6
can
be
represented
by
a
straight
line
with
a
slope
of
—0.36°C'
and
a
correlation coefficient
of
r
=
0.977.
Munro
and
co-workers
°
studied
the
behavior
of
three
pilot
-
scale
dewatering
machines
between
20
and
50°C.
The
re-
sults
gave
dependencies
of
moisture
content
(%w/w)
on
temperature
of
—0.11°C
1
for
the
roller
press,
—0.94°C
1
for
the
screw
press,
and
—0.83°C'
for
the
decanter
centri-
fuge.
The
low
temperature
dependency
of
the
roller
press
was
attributed
to
the
simple
one-dimensional
pressing
in
the
roller
press
which
does
not
expose
new
material
to
the
1156
BIOTECHNOLOGY
AND
BIOENGINEERING,
VOL.
32,
OCTOBER
1988
drainage
surface,
and
to
sealing
of
the
drainage
surface
at
high
temperatures.
Centrifugal
dewatering
in
a
batch
labo-
ratory
centrifuge
employs
simple
one-dimensional
water
removal,
but
there
is
no
perforated
drainage
surface
so
sur-
face
sealing
does
not
occur.
An
intermediate
value
for
tem-
perature
dependency
might
therefore
have
been
expected.
Effect
of
Casein
Manufacturing
Variables
on
Moisture
Content
Precipitation
pH
had
a
marked
effect
on
curd
moisture
content
before
centrifugation,
and
a
less
pronounced
effect
on
dewatered
curd
moisture
content
(Fig.
7).
The
effect
of
precipitation
pH
on
casein
curd
properties
is
well
known
with
a
high
precipitation
pH
producing
large,
strong
curd
particles
with
a
comparatively
low
moisture
content
and
usually
a
high
calcium
content:
0
'
13
'
14
These
effects
are
at-
tributed
to
electrostatic
repulsion
below
the
isoelectric
point
and
to
calcium
binding
above
the
isoelectric
point.
Increasing
the
hot
wash
temperature,
i.e.,
the
maximum
washing
temperature
encountered,
caused
a
small
but
sig-
nificant
decrease
in
curd
moisture
content
both
before
and
after
centrifugation
(Fig.
8).
The
shrinkage
of
casein
curd
at
high
washing
temperatures
is
generally
regarded
as
re-
versible.
11
''
2
However,
the
results
in
Figure
8
indicate
some
irreversible
changes
to
the
curd
on
exposure
to
high
wash-
ing
temperatures.
Hobman
and
Hughes"
found
that
hot
wash
temperature
had
an
important
effect
on
casein
grind
-
ability
with
higher
hot
wash
temperatures
making
casein
easier
to
grind.
This
also
suggests
irreversible
changes
to
the
curd
on
exposure
to
high
washing
temperatures.
The
financial
support
of
New
Zealand
Dairy
Research
Institute
(NZDRI),
Palmerston
North,
for
a
previous
study
on
"Dewatering
of
Dairy
Protein
Precipitates,"
is
gratefully
80
cu
4-
0
60
cu
in
O
50
42
0
4.5
4.8
51
pH
Figure
7.
Curd
moisture
content
(0)
before
and
(0)
after
centrifugation
vs.
precipitation
pH
for
curd
centrifuged
for
20
min
at
30°C
and
4060g.
80
7
0
4-
-4-
c
60
C1J
L
VI
0
50
50
60
70
Temperature
(I)
80
90
Figure
8.
Curd moisture
content
before
(0)
and
(II)
after
centrifuga-
tion
versus
hot
wash
temperature
for
curd
centrifuged
for
20
min
at
30°C
and
4060g.
acknowledged.
The
work
of
J.
P.
Dyer,
R.
A.
King,
and
T.
W.
Fraser,
students
in
the
Department
of
Chemical
and
Materials
Engineering,
University
of
Auckland,
in
devel-
oping
the
methods
used
in
this
study
is
gratefully
acknowl-
edged.
P.
D.
Elston
(NZDRI),
C.
R.
Southward
(NZDRI),
and
R.
M.
McDonald
(Ruakura
Agricultural
Research
Cen-
tre,
Hamilton)
provided
valuable
discussions
during
the
course
of
this
work.
References
1.
D.
J.
Bell,
M.
Hoare,
and
P.
Dunnill,
Adv.
Biochem.
Eng.,
26,
1
(1983).
2.
U.
Wiesmann
and
H.
Binder,
Adv.
Biochem.
Eng.,
24,
119
(1982).
3.
C.
R.
Southward
and
N.
J.
Walker,
in
CRC
Handbook
of
Processing
and
Utilization
in
Agriculture,
Vol.
1,
Animal
Products,
I.
A. Wolff,
Ed.
(CRC,
Boca
Raton,
FL,
1982),
pp.
445-552.
4.
J.
T.
Vu
and
P.
A.
Munro,
New
Zealand
J.
Dairy
Sci.
Technol.,
16,
265
(1981).
5.
P.
D.
Elston,
21st
Int.
Dairy
Congr.,
Brief
Commun.
,
Vol.
1,
Book
2,
67
(1982).
6.
P.
A.
Munro,
J.
T.
Vu,
and
R.
B.
Mockett,
New
Zealand
J.
Dairy
Sci.
Technol.,
18,
35
(1983).
7.
C.
F.
Lockyear,
Effluent
Water
Treatment
J.,
19,
223
(1979).
8.
C.F.
Lockyear
and
M.
J.
D.
White,
"The
WRC
thickenability
test
us-
ing
a
low
-speed
centrifuge,"
Water
Research
Centre
Technical
Re-
port
118,
Water
Research
Centre,
Stevenage,
England,
(1979).
9.
V.
I.
Sokolov
and
A.
D.
Sedov,
Molochnaya
Promyshlennost'
,
8,
24
(1984).
10.
M.
S.
Jablonka
and
P.
A.
Munro,
J.
Dairy
Res.,
52,
419
(1985).
11.
G.
M.
O'Meara
and
P.
A.
Munro,
New
Zealand
J.
Dairy
Sci.
Tech-
nol.,
17,
147
(1982).
12.
P.
A.
Munro
and
B.
K.
Tan,
J.
Chem.
Technol.
Biotechnol.,
34B,
279
(1984).
13.
M.
S.
Jablonka
and
P.
A.
Munro,
J.
Dairy
Res.,
53,
69
(1986).
14.
M.
S.
Jablonka
and
P.
A.
Munro,
New
Zealand
J.
Dairy
Sci.
Tech-
nol.,
21,
111
(1986).
15.
P.
G.
Hobman
and
I.
R.
Hughes,
New
Zealand
J.
Dairy
Sci.
Technol.,
12,
242
(1977).
MUNRO
AND
VAN
TIL:
CENTRIFUGAL
DEWATERING
OF
ACID
CASEIN
CURD
1157