Integrierte Vermeidung und Verminderung der Umweltverschmutzung

Chapter 2
Colours and flavours are added at the ageing stage. Continuous freezers are used to rapidly
freeze the ice-cream down to around -6 ºC, with compressed air being introduced into the icecream
during the freezing process. The increase in volume due to the addition of air is known as
over-run. The ice-cream is filled into containers and frozen further in tunnel freezers operating
at -30 to -40 ºC.
2.2.5.7 Whey
Whey is normally evaporated to a supersaturated solution with a total solids content of
60 to 73 % to produce lactose. In cooling down the solution, crystallisation starts and the
crystals begin to grow. The crystals are removed from the liquid phase by centrifugation.
Depending on the required grade, further purification or refining can take place by washing the
crystals, or redissolving them and recrystallising them, followed by treatment with active carbon
for the removal of any impurities.
2.2.6 Grain mill products
There are a number of cereals important as food sources. These include wheat, barley, maize,
oats, rye and rice. Wheat and rye grain is milled into flour. Durum wheat is milled into semolina
and is generally used to make pasta. Wheat is the prime ingredient used in the manufacture of
products such as bread and biscuits. In some countries, rye is used for bread. Barley is mainly
used for animal feed. Barley of a certain quality is processed to malt and then used, e.g. in
brewing and distilling. Maize is used as a source of starch but also as an ingredient in breakfast
cereals and snack foods. Oats are used for cereals, cakes, biscuits, and also for making
crispbread. Rice, along with wheat and maize is one of the major cereals of the world and is the
basic food for much of the world’s population. Rice is pearled and sometimes precooked.
The wheat grain has three main components, the skin or bran, the embryo or germ, and the
endosperm, which makes up the majority of the grain. The object of the milling process is to
separate the endosperm with minimal contamination from the bran and germ. The main
operations associated with flour milling are cleaning, conditioning, breaking, scalping,
purification, reduction and dressing.
The incoming grain is transferred to bulk silos prior to further processing. Gas or heat treatment
may be applied to prevent insect infestation. The grain is first washed by passing through a
series of screening, scouring, brushing and aspiration operations. These processes remove
extraneous matter such as other cereals, stones, metal contaminants, chaff, loosened bran layers,
seeds and dust. After washing, the grain is conditioned to optimise the milling process. This
involves dampening the grain by the measured addition of water, which immediately binds the
kernels. Conditioning may be made by using steam. Conditioning has a number of functions,
such as toughening the bran, and thereby improves the separation of the bran from the
endosperm, allowing the endosperm to be reduced more effectively in subsequent stages of the
process.
The conditioned grain enters the break system of the mill, which consists of pairs of corrugated
rollers which revolve in opposite directions and at different speeds. Five sets of break operations
are common, with the aperture gradually decreasing and the corrugation becoming finer
between subsequent sets. The grain is split by the break-rollers and the endosperm is scraped
from the bran. A screening operation known as scalping or grading is carried out after each
break-roller. This operation separates:
• coarse particles which contain the remains of the grain and some endosperm which is yet to
be recovered
• particles of intermediate size which contain chunks of endosperm which are called
semolina or middlings, depending on their particle size and purity
• flour.
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