Continuous-screw pressing

Equipment used in pressing has shown considerable change in the last twenty years. Until 1960, most red pomace was pressed in vertical hydraulic basket presses. In the 1960s and 1970s, the Willmes-type pneumatic horizontal bag press as well as horizontal screw presses became popular. These were batch process operations. More recently, horizontal continuous screw presses preceded by an inclined dejuicer have appeared in the North Coast and will probably increase in popularity. They are designed to separate automatically different grades of press juice (Figure 5). 

Separation of oil from crushed seed by draining squeezing cooked mash in cloths by lever, wedge or hydraulic presses continuous screw presses, or by solvent extractors. 

Continuous screw presses are used (1) for extracting fats and oils in small operations where investment capital or supplies of raw materials are limited and installation of a solvent extraction plant is impractical (2) to partially defat high-oil content seeds for easier handling in subsequent solvent extraction or hard pressing and (3) for extraction of animal flesh and bones, fish, and fleshy-type oilseeds such as palm fruit, olives, and copra (dried coconut meat ), and oilseeds. These machines have been generically referred to as expellers, but the Expeller trademark belongs to Anderson International Corporation, Cleveland, OH, successor to the company founded by Valerius D. Anderson who patented the first continuous screw press in 1899. 

Oil Extraction. Oil extraction is generally carried out using continuous screw presses comprising a perforated horizontal cage of a hgure 8 cross section in which two screws or worms run. A cone at the discharge end of the cage controls the pressure to ensure a minimum of residue oil in the press cake with an acceptable amount of broken nuts. 

The extraction of sesame oil from roasted sesame seed is generally performed with pressing. Solvent extraction is not used because the desirable roasted flavor may be removed during evaporation of solvent. In commercial production, continuous screw-press or hydraulic press is employed (42). The hydraulic press can be vertical or horizontal. The continuous screw may be operated twice in order to increase the oil yield (82). Proper cooking (100°C, 7 min) and addition of water (12.5%) after roasting can also raise the oil yield (83). 

The processing of soybeans has been described in more detail elsewhere than can be done here (132-134). Oil is recovered today by either mechanical means or through the use of organic solvents. In the preindustrial revolution period, soybeans were merely pressed with lever or animal-driven screw-operated batch presses. Around the turn of the Twentieth Century, when soybeans became a viable commercial crop in the United States, steam-powered hydraulic batch presses were used. Today, electric-powered continuous screw-presses, often referred to as expellers (but this is a trademarked name for screw presses manufactured by one supplier), or continuous countercurrent solvent extractors are used. 

Hydraulic press oil mills remained in use as late as the 1950s before the last of them were replaced with continuous screw presses and continuous solvent extraction plants, both of which required far less labor and could process at much higher rates. 

Manually operated presses, using jack screws to apply pressure, have been used for hundreds of years. Hydraulic cylinders made the presses more efficient and less labor intensive. The greater pressure generated by a hydraulic cylinder liberated more oil. In the early 1900s, hydraulic presses dominated the oilseed crushing industry. However, even then they were considered labor intensive. Valerius D. Anderson, as will be discussed in Section 4.2, had already developed a continuous screw-press, but it was 20-30 years before it swept through the animal fat and oilseed crushing industries. 

Today, continuous screw-presses dominate the mechanical extraction of fats. The only applications still favoring hydraulic presses are those requiring gentle handling, for example, pressing cocoa butter from cocoa beans where the defatted residue is to be fine-ground to make cocoa powder. The development of continuous screw-presses will be outlined in Section 4.2. The development and technology of hydraulic presses was covered in detail in previous editions of this book (109). This edition briefly summarizes the early development of hydraulic presses and then focuses on modern, continuous cocoa butter hydraulic presses used today. 

In the early 1900s, this new continuous screw-press, being immensely less labor intensive than hydraulic presses, revolutionized the crushing industry. It found ready acceptance in the pressing of animal residues as well as oilseed materials. In 1900, Anderson registered the trade name Expeller (111) for the screw-press. The name is still registered to Anderson. 

Most oilseeds and animal residues have a sufficient history of being pressed in continuous screw-presses. Therefore, all screw-press manufacturers have field-proven... 

Obtained by solvent extraction using petroleum hydrocarbons, or to a lesser extent by expression using continuous screw-press operations, of the seeds of either Glycine max (Leguminosae) or Glycine soja (Leguminosae). The oil is refined, deodorized, and clarified by filtration at about 0°C. Any phospholipids or sterols present are removed by refining with alkali. 

The preparation of soy protein products is described in this chapter, from the simpler to the more complex, but the technology did not develop in such an orderly fashion. Crude forms of SF were sold in the United States as early as 1926, as health flours (Smith Circle, 1972). SFs were initially made from whole soybeans, then from batch hydraulic-pressed or continuous screw-pressed (expeller) cakes, and later from solvent-extracted meals. 

Palm oil is the pulp oil extracted promptly after harvesting from the fleshy mesocarp of the oil palm fruit using continuous screw presses. The liquid coming from the press is a mixture of oil, water and non-oily solids (NOS). After separation from sludge in a setthng tank, clarification, purification and vacuum drying, crude pahn oil (CPO) is yielded from the press liquid. 

Prepress solvent extraction. In this process the oil-bearing material are first mildly pressed mechanically by means of a continuous screw press operation to reduce the oil by half to two-thirds of its original level before solvent extraction to remove the remaining oil in the pre-pressed cake. Pressing follow by solvent extraction is more commonly used when high oil content materials (e.g., canola/rapeseed, flaxseed, com germ) are processed. 

Extraction of oils has largely relied on mechanical or heat rendering process for centuries. Increased demand of productivity to separate oils from oilseeds has been the principal factor driving the changes of oilseed processing from the ancient hydraulic press to a continuous screw press or expeller in early 1900 s. This operation still left more than 4-5% residual oil in the pressed cake. More complete recovery of oil can only be effectively accomplished by solvent extraction. ... 

Some odier products that can be liandled by continuous screw presses are ... 

Pructning hi the United States, extraction of the ol is largely by the continuous screw-press solvent extraction method. 

Much of the fish that is processed is cooked in batch or continuous cookers to coagulate the protein, and passed through a continuous screw press to remove the liquid portion. The liquid then is separated by continuous decanters... 

Ward J. 1976. Processing High Oil Content Seeds in Continuous Screw Presses. J. Am. Oil Chem. Soc. 53(6) 261-264. 

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