DRY MILLING TECHNOLOG shallow (dull) profile disposed towards the case of water the separation usually depends on nip The relationship between rolls may thus one or more component being denser than water be described as 'dull-to-dull, sharp-to-sharp and others being less dense. When air is used, dull-to-sharp or sharp-to-dull(Fig. 6.2). It the force of an air current supports particles of is conventional to give the fast roll disposition lesser density to a greater degree than the denser first in such descriptions ones, allowing them to be carried upwards and 2. Flaking flaking rolls are smooth-surfaced later deposited when the force of the current is and are generally heavier than grinding rolls reduced The process is described as aspiration and they are operated at zero differential. TheThe lighter particles frequently also have a purpose of this is to increase the surface area flat shape which enhances their buoyancy. of the feedstock, either to facilitate subsequent Aspiration features in purifiers used in wheat separation of components(eg. germ from (particularly durum) milling to remove bran from endosperm) or to impart desired product semolina, and in rice milling, to remove pearling haracteristics, as in porridge oats from decorticated grains Multiple factors Grains or milled stocks are thrown against a hard and possibly abrasive surface. This is usually The paddy separator(see p. 120)is an example achieved by feeding stocks into the centre of a of a machine in which several grain characteristics very high-speed rotor. The process is very versatile are exploited in effecting their separation. Specific It be used means of dehulling (as of gravity, surface roughness and shape all combine ats), abrading, size-reduction, (as in pin milling), to direct grains into appropriate streams on a or disinfestation, destroying all stages in the life- tilted vibrating table with a cunningly sculptured cycle of insect pests found in grain and four surface Fractionating processes Changes in temperature and/or moisture Water can be added with or without substantial hich involve grinding, sieving features at some physical conditions, as in stabilization of oats,or tage, to separate stocks as final products or for to change the mechanical properties of the grain further appropriate treatment components, as in wheat and rice milling, when the temperature is of less importance Shape Stocks produced from grains or intermediates processes suc h as oat milling and rice milling milled at very high moisture need to be dried to grains are graded on a shape(and size)basis, before permit proper processing or safe storage. Drying dependent; and during the milling process, as small been heated may subsequently require cooling grains which escape treatment need to be re-fed Shape-sensitive fractionating machines include Fine grinding and air classification disc separators and trieur cylinders The contents of cells comprising the bulk of Specific gravity storage tissues of many legume cotyledons and cereal endosperms consist essentially of starch Particles differing in density may be separat granules embedded in a protein matrix. In oats on a fuid medium such as air or water. In the and some legumes an appreciable amount of oilDRY MILLING TECHNOLOGY 131 shallow (dull) profile disposed towards the case of water the separation usually depends on nip. The relationship between rolls may thus one or more component being denser than water be described as ‘dull-to-dull, sharp-to-sharp, and others being less dense. When air is used, dull-to-sharp or sharp-to-dull’ (Fig. 6.2). It the force of an air current supports particles of is conventional to give the fast roll disposition lesser density to a greater degree than the denser first in such descriptions. ones, allowing them to be carried upwards and 2. Flaking - flaking rolls are smooth-surfaced later deposited when the force of the current is and are generally heavier than grinding rolls reduced. The process is described as aspiration. and they are operated at zero differential. The The lighter particles frequently also have a purpose of this is to increase the surface area flat shape, which enhances their buoyancy. of the feedstock, either to facilitate subsequent Aspiration features in purifiers used in wheat separation of components (eg. germ from (particularly durum) milling to remove bran from endosperm) or to impart desired product semolina, and in rice milling, to remove pearlings characteristics, as in porridge oats. from decorticated grains. Multiple factors The paddy separator (see p. 120) is an example of a machine in which several grain characteristics are exploited in effecting their separation. Specific gravity, surface roughness and shape all combine to direct grains into appropriate streams on a surface. Changes in temperature and/or moisture content Water can be added with or without substantial change in temperature, it may be added specific￾ally to achieve a required combination of the two physical conditions, as in stabilization of oats, or to change the mechanical properties of the grain components, as in wheat and rice milling, when the temperature is of less importance. Stocks produced from grains or intermediates milled at very high moisture need to be dried to permit proper processing or safe storage. Drying is performed by heating, and stocks that have been heated may subsequently require cooling. Fine grinding and air classification The contents of cells somprising the bulk of storage tissues of many legume cotyledons and cereal endosperms consist essentially of starch granules embedded in a protein matrix. In oats and some legumes an appreciable amount of oil Impacting Grains or milled stocks are thrown against a hard and possibly abrasive surface. This is usually achieved by feeding stocks into the centre of a very high-speed rotor. The process is very versatile; it may be used as a means of dehulling (as of or disinfestation, destroying all stages in the life￾cycle of insect pests found in grain and flour. Fractionating processes Size This is an important criterion by which par￾ticles are separated. In most milling systems which involve grinding, sieving features at some stage, to separate stocks as final products, or for further appropriate treatment. Shape In processes Such as Oat milling and rice milhgy grains are graded on a shape (and size) basis, before treatment, as machine clearances are grain-size dependent; and during the milling process, as small grains which escape treatment need to be re-fed. Shape-sensitive fractionating machines include disc separators and trieur cylinders. Specific gravity Particles differing in density may be separated on a fluid medium such as air or water. In the Oats), abrading, size-reduction, (as in Pin milhg)Y tilted vibrating table with a cunningly sculptured