Pressing processes.

With many oil-bearing seeds and nuts, rendering will not liberate the oil from the cellular structures in which it is held. In these cases the cell walls are broken by grinding, flaking, rolling, or pressing under high pressures to liberate the oil. The general sequence of modern operations in pressing oilseeds and nuts is as follows:

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1) the seeds are passed over magnetic separators to remove any stray bits of metal; 2) if necessary, the shells or hulls are removed;

3) the kernels are converted to coarse meal by grinding them between grooved rollers or with special types of hammer mills; and

4) they are pressed in hydraulic or screw presses with or without preliminary heating, depending on the type of oil-bearing material and the quality of oil desired.

Oil expressed without heating contains the least amount of impurities and is often of edible quality without refining or further processing. Such oils are known as cold-drawn, cold-pressed, or virgin oils. Pressing the coarse meal while it is heated removes more. Such oil is more highly coloured than cold-pressed oils. Residual meals are concentrated sources of high-quality protein and are generally used in animal feeds.

Exercise 2. Translate the following word-combinations.

Cold-pressed oils, the coarse meal, oil-bearing material, during deshelling operation, the least amount of impurities, the corn-milling industry, extracting with volatile solvents, any stray bits of metal, over the magnetic separators, without preliminary heating.

Exercise 3. Complete each sentence with a word or phrase from the box.

preliminary heating raw materials grooved rollers magnetic separators mechanical presses

1. The ___ for the oil industry are fleshy fruits and various oilseeds.

2. One of the most popular methods of recovering oils from the oilseeds is pressing with ___. 3. To remove any stray bits of metal seeds are passed over ___.

4. Pressing operations may be carried out in hydraulic or screw presses with or without ___. 5. In pressing ___ are used for grinding kernels to convert them into coarse meal.

Exercise 4. Checking facts and ideas. Decide if these statements are true or false.

1. Corn oil is obtained from the corn specially grown for this purpose. 2. Virgin oils do not require refining or further processing before eating. 3. Cold-drawn oils are more highly coloured than warm-pressed oils.

4. Residual meals are generally used in animal feeds.

5. Rendering, pressing and extracting are of the same mechanical simplicity.

Exercise 5. The purpose of preparation is to modify the seed into a shape that is suitable for fast and effective extraction by mechanical pressing or by solvent extraction. Match the preparation processes with their purposes.

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