| Supply / Cleaning
After the delivery the potatoes are coarsely cleaned for removal of
soil and stones and then stored. They are transported into the factory
by flumes, which are equipped with strow and stone separators. The main
cleaning is conducted in a trough washing machine where the potatoes are
spinned around. Constant abrasion completely removes soil and also most
of the skin. The washing water is then pumped into clarification pools
for sand and stone removal and reintroduced into the process.
Rasping
The purified potatoes are mashed by means of a rotary saw blade rasp.
In these rasps rows of saw blades are closely arranged on a drum which
is driven by high rotation speed. Sharp saw teeth convert the potatoes
into a fine mash. This process results in an almost complete disruption
of the potato cells, which therefore release the starch. Simultaneously
the potato skins are only roughly torn. This is inevitable to avoid that
fine skin fragments pass through the sieves during the following extraction
step and remain in the starch, which would lead to poor starch quality.
Extraction and fruit water separation
Firstly coarse skin and cell fragments, the so called pulp, have to
be separated from the rasped potatoes. This separation step is conducted
by means of conical rotating sieves, the so called centrisieves. For better
starch isolation water is applied to the sieves through nozzles. While
starch and fruit water passes through, the fibres are retarded by the
sieves. The remaining pulp is drained or pressed off and used directly
as feed while still damp or dried in flash dryers. The pulp is used as
mix feed because of its high feed value because of its protein and residue
starch content.
In the next step, the fruit water is separated in several steps by means
of hydro-cyclone plants. Separated fruit water has a high content of proteins,
amino acids, and mineral nutrients. About one half of the soluble proteins
are coagulated by treatment with acid and heat and then separated in decanters.
The remaining fruit water is evaporated and used for fertilizing.
Dewatering and drying
Refined starch milk has a dry matter content of about 35 % to 40 %.
The starch is dewatered by rotary vacuum filtration to moisture contents
below 40 %.
Drying is conducted by means of a flash dryer. Starch must not exceed
15 % of residual moisture to be suitable for storage.
|
