Separator's Digest - GEA Westfalia Separator Group

are En Vogue
FrUiT jUicE anD FrUiT pUrEE prODUcTiOn
wiTh DEcanTErS
however, a high-quality end product not
only requires perfect raw materials:
correspondingly high-quality processing is
just as important. This means that lower
quality and rotten constituents of the raw
products have to be removed. crushing and
mash treatment are mandatory and have to
be used in accordance with the specific type
of fruit. in many cases, peeling and stoning
of the fruit are recommended for making
quality products.
Rapid juicing, short
processing times
an attempt is made to avoid the use of heat
and enzymes. Long processing times have
an even greater negative impact on quality.
after fruit has been crushed, enzymes such
as pectinases and oxydases are released;
these result in a biochemical change in the
juice.
Lengthy exposure to atmospheric conditions
results in a not necessarily desired change in
aroma and colour. For instance, in the
production of apple juice, the aroma is
released after the apple has been crushed.
in the initial phase, the concentration of key
components increases, and the aroma
becomes more intense. however, over a
period of time, these components change
or disappear. This process is normally
stopped by means of pasteurisation
involving heat treatment. ideally, the juice is
heated ten minutes after it has been
crushed. in order to be able to achieve this,
it is essential for the fruit to be juiced quickly,
for instance with a decanter. The very short
processing time also has the major
advantage that the microbic contamination
time is minimised. This results in a low
bacteria process.
Decanters as the core
element of process
technology
when a decanter is used, the mash is
conveyed through a feed tube into the bowl
which is rotating at high speed. The
centrifugal force in the bowl results in the
solids with a higher specific gravity being
separated from the mash, and the solids
then collect on the wall of the bowl. The
lighter phase, the juice, collects above the
solids. The solids scroll rotates at a slightly
higher speed in the bowl of the horizontal
scroll-type centrifuge. The solids are
discharged out of the bowl by the scroll as a
result of the slightly higher differential
speed. The solids first enter the conical part
of the decanter bowl, where they are further
juiced before being discharged out of the
bowl. This juicing process is based on the
process of the solids being lifted out of the
liquid layer and being subject to downstream
press dewatering (in the case of compressible
solids, such as most fruit mashes) or
dewatering by means of capillary flow (in
the case of incompressible solids).
ideal processing conditions can be created
by the choice of suitable technical parameters.
This is achieved by ensuring that the
technical parameters are consistent with
the process environment. The mash processing,
and in particular the crushing
process, is vital in most cases.
Adjustable consistency
Because smoothies are a mixture of fruit
juice and purees, it is important for the right
solid content of the individual fruit
components to be set. in certain cases, it is
important to retain a “coarse“ consistency.
a homogeneous structure, such as that
achieved by means of a homogeniser, is
desired only in exceptional cases. The
concentration of the solid phase in the liquid
phase is controlled by the various machine
parameters which can be adjusted during
operation. The concentration can be
increased or decreased depending on the
phase in which the required substances
occur in increased concentration.
accordingly, the decanters should be fitted
with devices for torque-dependent control
of the differential speed, variable adjustment
of pond depth in ongoing operation and
product discharge under pressure by means
of a centripetal pump.
raTE capaciTy carEFULLy
The market requires high quality fresh fruit juices and fruit
purees, smoothies. This requires a processing line which meets
the requirements of high quality processing. A processing
capacity of 800 kg / h has proven to be a good scale.