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Chapter 23 Separation Techniques: Mechanical and Chemical Methods
fi rst grain mills ground dried grain kernels between two moving
stones. The weight or pressure of the stones crushed the grain into
fi ne particles. Although some small specialty mills still grind grain
between moving stones, most mills use metal rollers. Today, milling
is moving kernels of grain between a series of rollers. The space
between the rollers gets progressively smaller.
The size of the particles produced by milling will vary with the
molecular structure of each part of the grain. The bran remains in the
largest pieces due to its high cellulose content. Because of its higher fat
content, the germ portion remains in larger pieces than the endosperm.
The dry protein and starch mixture that makes up the endosperm
crumbles into the smallest particles and is called fl our.
Once grain is ground, the parts of the kernels are separated for
further processing and distribution. For example, ground corn is
separated so oil can be extracted from the germ portion. Presses are
used to squeeze oil from the germ.
Magnetic Force
Another type of force used to separate some food components
is magnetic force. Magnets will attract or pull iron and steel toward
them. This force has been used to help separate nutshells from the
meats of nuts. The shells are coated with a thin fi lm of an iron solution.
The nuts are dried and the shells are broken. The shells are easily
separated from the nut meats when the two components are conveyed
past magnets. Magnets are also used to remove metal fi lings that
may enter food mixtures during processing.
Combination Separation Processes
The separation of many food components requires a combination
of mechanical processes. For instance, olive, corn, canola, and other
vegetable oils come from the seed or fruit portion of plants. The oil
is suspended in solutions within cell membranes. Presses are used
to rupture or break the membranes and separate the oil and juices
from the plant solids. Then the liquid is centrifuged to separate the
oil from the water-based juices. Chocolate, soy, and sugar cane are
among the complex mixtures that must undergo several types of
separation processes.
Chemical Separation
Some food components are separated by chemical means.
Chemical separation requires a grasp of the physical and chemical
properties of foods. Chemical separation methods include the use of
solvents, crystallization, precipitation, evaporation, and distillation.