Integrierte Vermeidung und Verminderung der Umweltverschmutzung

2.1.2.2 Mixing/blending, homogenisation and conching (B.2)
2.1.2.2.1 Objective
Chapter 2
The aim of this group of operations is to obtain a uniform mixture of two or more components
or to obtain an even particle size distribution in a food material. This can also result in improved
characteristics and eating quality.
2.1.2.2.2 Field of application
These operations are widely applied in almost all FDM sectors.
2.1.2.2.3 Description of techniques, methods and equipment
Mixing or blending is the combination of different materials. The spatial distribution of the
separate components are reduced to obtain a certain degree of homogeneity. Various mixing
operations can be distinguished in the FDM sector.
Mixing solids with solids is carried out, e.g. during the production of animal feed, blends of tea
and coffee, dried soup, cake mixes, custard, ice-cream mixes and malt blends. Mixing
equipment commonly used includes rotating drums, rotary mixers, paddle and ribbon mixers
and mixing screws in cylindrical or cone-shaped vessels and variable speed drive screws.
Generally, cyclones are used as an integral part of the process to recover dust from the extracted
air. The recovered material is then reprocessed.
Mixing solid with liquid is carried out, e.g. during the production of canned foods and dairy
products. This type of mixing is also used in, e.g. the production of chocolates and sweets,
where the ingredients are mixed in a more or less liquid state and solidify on cooling. For
viscous mixtures, kneading machines are used. For low viscosity mixtures various types of
stirrers, impellers and agitators are used.
Mixing liquid with liquid is carried out, e.g. during the production of emulsions like
mayonnaise, margarine and mixtures of solutions. This type of mixing is also used to blend
different wines or mineral waters with each other or with additives or extra ingredients. Various
types of stirrers, impellers and agitators are used.
Finally, mixing liquid with gas is carried out, e.g. when making ice-cream, whipped cream and
some sweets. During spray drying, the liquid-phase is mixed in a stream of gas. Atomisers are
used to produce small liquid droplets, which are brought into contact with a stream of gas.
When making ice-cream, whipped cream or a foam, small gas bubbles are fed into a liquid.
The aim of homogenisation is to attain a more even particle size or a more homogeneous blend
of materials. It is, e.g. applied to whole milk to reduce the size of fat globules so that they stay
evenly divided in the milk, thereby preventing the fat separating and the cream rising. The
liquid, i.e. whole milk, is pressed under high pressure, 200 to 300 bar, through a small orifice.
Conching is a special method of kneading used in the chocolate industry. The molten chocolate
mass is placed in a special trough-shaped vessel and is kneaded by a granite roller moving
slowly back and forth. The aim of conching is to reduce the viscosity of the mass and to
improve the flavour and the texture.
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