OILSEEDS, OILS, AND FATS

Oil Processing Through the Ages

K. S. Markley.

What it might be asked do the chocolate coating of a candy bar, creamy white shortening, and a bar of soap have in common? They and a thousand more everyday products are made partly or entirely from fats and oils, which people in all times and climes have depended on for medicinals, cosmetics, lubricants, and illuminants.

The story of their development, told now in the light of the advances this generation has made in age-old processes, reveals how chemist and technologist have enhanced the value and broadened the market for farm products through increased efficiency and lower costs of processing, recovery of byproducts, and development of new products.

Probably the first fats used by man were of animal origin tallows and greases which were separated from other tissue simply by heating or boiling with water. Extraction of oil from fruits and seeds called for more vigorous treatment. As animal and vegetable oils were used from the time of the earliest records, methods for their separations must have been worked out before the dawn of history. The ancient Egyptians and Phoenicians used vegetable oils for food and for anointing their bodies, but not for illumination. The Egyptians used olive oil as a lubricant in moving large stones, statues, and building material. As early as 1400 B. C., Egyptian chariot wheels were lubricated with axle greases consisting of fat and lime. Earthen vessels predating the First Dynasty have been found which contained several pounds of oxidized palm oil. From the Egyptians and Phoenicians, knowledge of how to apply fats and oils spread to the Hebrews, and thence to the Greeks.

THE HEBREWS had oil mills powered by treads that usually were operated by prisoners. Pliny left the earliest description of an oil mill, which was used to crush olives. It resembled the ordinary edge runner, the stones being flat on the inner side and convex on the outer side. The Greeks and Romans are said to have employed screw presses similar to wine presses for recovering olive oil.

The wedge press was used in very early times in the Orient, particularly in China, where it is still operated. Another type of extractor, known as ghani, chekku, or kolhu, was developed long ago in India. It operates on the principle of a pestle rotating in a mortar and is often powered by bullocks. The mortar is generally made of wood, but in some parts of India may be made of granite. The ghani is still used in remote rural areas of India. The wedge press was revived in the seventeenth century as the Dutch stamper press powered by windmills.

Wedge, edge-runner, and screw presses were used in Europe for oilseed processing until the invention of the hydraulic press. Their efficiencies were increased somewhat by precrushing and heating the seed in the presence of moisture, a practice in use today.

The development of the hydraulic press in 1795 made possible a marked increase in the recovery of oil. In its earliest form, this press was an adaptation of the wedge press, with hydraulic power substituted for that obtained by wedges and falling weights. By 1815, improved forms of the hydraulic press were introduced in France and Germany, where their use spread rapidly.

In the first hydraulic presses, bags of ground seed or meal were placed in a perforated metal cylinder surrounded by another metal cylinder. Pressure from a hydraulic ram pushed the bags upward against a fixed plate, squeezing out the oil from the seeds into the outer cylinder. The bags were a source of trouble and expense and were soon replaced by molded cakes wrapped in press cloths. A series of horizontal plates, between which the molded cakes could be placed and pressed, replaced the boxes that held the bags in the old presses. This press, commonly referred to as the plate or Anglo-American press, has been used in much of the world for processing many types of oilseeds. It has changed but slightly in the past 75 years.

A modification of the plate press, known as the cage press, was developed later, but, although relatively efficient, it is used much less widely than the plate press. Although the plate and cage presses made possible a much greater recovery of oil than was possible with the wedge press, the new presses still left 7 to 10 percent of oil in the cake.

The twentieth century brought a virtual revolution in the mechanical methods of processing oilseeds. An American invention, a machine for continuously pressing oil-bearing materials, was responsible. The new machine, still in use, is described in another chapter of this book.

The original continuous screw press, or expeller, was improved and built in increasingly larger capacities. The rise of the soybean-processing industry in the United States in the 1930's created a further demand for these presses. Efficiency, as well as capacity, increased until it became possible to process soybeans so as to reduce the residual oil content of the cake to 3.5 or 4.5 percent.

Oil technologists were not satisfied to leave even this amount of oil in the extracted cake, but efforts to reduce it appreciably below 3.5 percent by mechanical means were not successful. Other means therefore were sought to reduce the oil content of the cake or meal. This was eventually accomplished by extracting the seed with an organic solvent, or by pressing it to remove part of the oil and then extracting the cake with a solvent to remove the rest.

The first practical process for the solvent extraction of oil from oilseeds was developed by Jesse Fisher in Birmingham, England, in the 1840's, but no patent for the solvent extraction of fatty oils was granted in England until 1856. Since that time numerous patents have been granted in Europe and in the United States. Solvent extraction has been practiced on a fairly large scale in Europe since 1870. The first extractors were single-unit, unagitated, batch vessels. Soon multiple-unit, agitated, countercurrent extractors appeared. Many attempts were made to develop a continuous solvent-extraction process, and about 1920 Herrmann Bollman in Germany developed an extractor that was especially adapted to the recovery of oil from soybeans. This extractor and its operation are discussed in detail in the following chapter.

The development of the Bollman continuous extractor was followed by many other types. One of these, also developed in Germany by Karl Hildebrandt is a combination of two vertical enclosed screw conveyors connected at the bottom by a cross conveyor so that the whole forms a U. The previously rolled or flaked oilseed moves in one leg in the same direction as the flow of the solvent, and in the other leg in the opposite direction.

This type of continuous extractor was introduced in the United States for processing soybeans in 1934 and was followed very shortly by the Bollmann, or paternoster, extractor. Somewhat later, an extractor of American design the rotating-plate, vertical gravity extractor was introduced. It was followed by a modified type known as the stationary-place extractor.

These three types of extractors are used in all but a few solvent- extraction plants in the United States; the first two are used in most of the continuous-extraction plants in Europe.