298 94 307/02 Untersuchungen zum Stand der Umsetzung des ...

Teil 3 Seite 6-18
ceous earth filter being followed by a filter that uses commercially available cellulose filter
pads, which are about 1 cm thick. The extract may pass a cloth filter bag first, to remove
residual coarse particles. During filtration the temperature of the solution is kept at 55 -
60 ºC.
The filtration equipment usually of the type used in several branches of the food industry
and is readily available. The diatomaceous earth filtration can be either pressure vacuum
operated. For pressure operated filtration the filter bed is in a closed vessel which is
pressurised. When the maximum pressure is reached, the filter meshes are automatically
cleaned and covered with new filter aid. For vacuum filtration the filter is usually a rotating
drum filter with the filter layer on the outside of the drum. The extract is sucked into the
inside of the drum. With this kind of filter, the filter aid and the layer is automatically
scraped off, so the filter has continuously a fresh surface.
G Ion exchange
The filtered extract is passed through an ion exchange resin to remove all dissolved salts
from the solution. With limed bone gelatine the solution normally first passes the cation
column and then the anion column. Most installations consist of two cation columns and
two anion columns of which one of each is in use, while the other two are either regener-
ating, or are on standby. Modern installations have an automatic control system that
changes the flow to the standby column as soon as the column in use reduces in effec-
tiveness and it starts the automatic regeneration procedure for the exhausted column.
Older installations are less automated. The cation and anion exchangers are regenerated
with approximately 5 % hydrochloric acid and approximately 5 % sodium hydroxide and
both are rinsed using de-ionised water. An example columns size is 157 cm diameter and
175 cm height. The flow through such a column is about 7000 litres/hour. During the ion-
exchange the temperature of the solution is generally kept at 55 - 60 ºC. The installations
are made of synthetic material or of plastic coated steel.
H Concentration
After the solution that comes from the ion-exchangers the next step is to concentrate it in
multiple-effect vacuum evaporators, this facilitates the removal of water at relatively low
temperatures. Different designs of evaporators can be used for this. The vapour ex-
tracted from the first effect is used to heat the second and that from the second is used to
heat the third. The heating and cooling is undertaken very quickly so that the product is
not damaged. At this stage in the process the solution is now about 20 - 30 % gelatine.
The equipment is made of stainless steel.
I Sterilisation
The concentrated gelatine solution is sterilised either by direct steam injection such that
the temperature is raised to 138 - 140 ºC or by operating the final effect at a temperature
of about 120 - 140 °C. If direct steam injection is used, the solution is kept at this tem-
perature during at least 4 seconds and a pressure of at least 4 bar is maintained. The
temperature of the gelatine is measured and monitored continuously. The sterilising
equipment is made of stainless steel.