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Modern Technology Of Oils, Fats & Its Derivatives

Author: NIIR Board

Format: PaperbackISBN: 8178330857Code: NI68Pages: 520

Price: Rs. 1,100.00 US$ 125.00

Published: 2002Publisher: National Institute of Industrial ResearchUsually ships within 3 days

The book contains the manufacturing processes and other related information ofimportant Oils, Fats and their derivatives. This is very helpful book for professionals,students, entrepreneurs and established one.

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Contents Hide

1. SOURCES, UTILIZATION, AND CLASSIFICATION OF OILS AND FATSClassification of Fats and OilsMilk Fat GroupLauric Acid GroupVegetable Butter GroupAnimal Fat GroupOleic-Linoleic Acid groupErucic Acid GroupConjugated Acid GroupMarine Oil GroupHydroxy Acid Group2. PHYSICAL PROPERTIES OF FATS AND FATTY ACIDSOiliness and ViscositySurface and Interfacial TensionDensity in the Solid StateDensity and Volume of Plastic Fats DilatometryHeat of CombustionSpecific Heats, heats of Fusion or CrystallizationVaporpressure and Boiling Points. Heat of VaporizationThermal ConductivityMiscibility with Organic SolventsSolubility in Organic SolventsMutual Solubility of Fats and Fatty Acids with Watersolubility of Gases In FatsRefractive IndexAbsorption SpectraResistance


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Dielectric Constant3. REACTIONS OF FATS AND FATTY ACIDSHydrolysisInteresterificationSaponification with Alkalies

Formation of Metal SoapsHydrogenation in the Carboxyl GroupFormation of Nitrogen DerivativesFormation of Acid ChloridesHydrogenationHalogenationAddition of ThiocyanogenAddition of Maleic AnhydrideSulfation, SulfonationChemical oxidation Epoxidation and hydroxylationAtmospheric oxidations Rancidity

PolymerizationIsomerizationReactions of Hydroxyl GroupsPreparation of Ketones, Aldehydes, and Hydrocarbons from Fatty AcidsPyrolysis to Produce Motor FuelsManufacture of Sebacic Acid4. VINYL LAURATE AND OTHER VINYLE ESTERS5. LINOLENIC ACID AND LINOLENYL ALCOHOLSome Reaction ProductsLinolenyl AlocoholLinolenyl AldehydesMiscellaneous6. FRACTIONATION OF FATS AND FATTY ACIDSFractional CrystallizationWinterization of Vegetable OilsCold Clearing of Fish OilsFractional Crystallization of animal FatsCrystallization of Vegetable StearinesFractional Crystallization of Fatty AcidsLiquid-Liquid ExtractionSolvents for Liquid-Liquid Extraction Liquid-Liquid Extraction In PracticeTheory and General PracticePurification of Fatty Acids by DistillationFractional Distillation of Fatty AcidsMolecular DistillationMethods Involving Chemical ReactionUrea AdductsChromatographyCountercurrent DistributionRecovery of Minor Constituents


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7. SOLIDIFICATION, HOMOGENIZATION, AND EMULSIFICATIONPlasticizing of lard and ShorteningsSolidification of MargarineSolidification of Soap ProductsEmulsification

Peanut OilMilling of GroundnutEffect fo Storage of Groundut Kernels of the Yield & Quality of Oils and CakeEffect fo Size Reduction of the Kernels Prior to CrushingCooking of Prepared Seed MaterialOptimum Quantity of Oils to be left in the First Pressed CakeSummary of The ResultsOlive OilPalm OilsSesame OilCorn Oil

Safflower OilTobacco Seed OilPoppyseed OilTeased OilKapok OilRice Bran OilSorghum oilOther Oleic-Linoleic OilsRapeseed OilOtherErucic Acid OilsLinolenic Acid OilsSoybean Oil (91)Perilla OilHempseed OilWheat Germ OilHorse FatOther Linolenic Acid OilsConjugated Acid oilsTung OilsOiticica oilIses in coatingIn ConclusionMarine OilsWhale OilSardine or Pilchard OilJapanese Sardine OilMenhaden OilHerring OilFish Liver OilsHyrdoxy Acid Oils


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Castory Oil8. KOKUMGarcinia Indica ChoisDescriptionFlowering And Fruiting

DistributionEstimation of Seed ProductionCollection of SeedsOil9. MAHUADescriptionFlowering And FruitingDistributionLocaity FactorsPropagationEstimation of Seed Production

Other Uses10. NEEMDescriptionflowering and FrutingDistributionLocality FactorsPropagationUsefulness in AfforestationEstimation of Seed ProductionCollection And Storage of SeedsOil Other Uses11. PUNNA, UNDIFlowering And FrutingDistributionLocality FactorsPropagationEstimation of Seed ProductionCollection of SeedsOilUses of the oilOther Uses12. KARANJDescriptionFlowering & FruitingDistributionLocality FactorsPropagationUsefulness in AfforestationEstimation of Seed ProductionCollection and Storage of Seeds


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OilUses of the oilOther uses13. KUSUMDescription

Flowering And FruitingDistributionLocality FactorsPropagationEstimation of Seed ProductionCollection of SeedsOilUses of the oil and Cake14. DHUPADescriptionFlowering and Fruiting

DistributionLocality FactorsPropagationEstimation of Seed ProductionCollection of SeedsFatUses of FatOther uses15. NAHORDescriptionFlowering and FruitingDistributionLocality FactorsPropagationEstimation of Seed ProductionCollection of seedsOilUses fo The oilRefining of oilOther Uses16. KHAKAN, PILUDescriptionFlowering And FruttingDistributionLocality FactorsPropagationUsefulness in AfforestationEstimation of Seed ProductionCollection and Storage of SeedsFat


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Other used17. PISADescriptionflowering and FruitingDistribution

Locality FactorsPropagationEstimation of Seed ProductionCollection and Processing of SeedOil18. TALL OILRecovery of Tal oilApplication of Tall oil19. TALL OIL PRODUCTS IN SURFACE COATINGSTall Oil in Alkyd ResingTall Oil Formulation in Alkyd Resins

Esters of Tall Oil ProductsOther Uses for Tall Oil Products20. TALL OIL IN THE PLASTICIZER FIELDTallate DriersEsterification of Tall Oil For PlasticizersTall oil in Adhesives and Linoleum CementTall oil In Rubber-Based AdhesivesTall Oil In Hot-Melt AdhesivesTall Oil Production in Linoleum CementsFormulation with Tall OilFormulation with Tall Oil EstersTall Oil in Asphalt Products and Petroleum usesTall Oil In AsphaltRoadsSoil TreatmentRoofingAdhesivesAntistripping AgentsPlasticizersMiscellaneousTall Oil In Petroleum ApplicationOil and Gas Well FracturingDrilling MudsDemulsification AgentsCorroson InhibitorsCatalystLubricating Oil Additives21. TALL OIL IN LIQUID SOAPSTall Oil In DisinfectantsTall Oil In Synthetic Detergents & Wetting Agents


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Tall Oil In Biodegradable Detergents22. TALL OIL IN RUBBERStyrene-Butadiene RubberFoam rubberTall Oil In Paper Size

Paper Making ProcessRosin Sizing MaterialsForms of Size AvailablePaste SizeDry SizeMethods of Proeparing Liquid SizeCooking ProcessEmulsion ProcessBewoid ProcessDelthirna ProcessInternal And External Sizing

Effect of Wet Strength Resings and Paper Coating Resins of SizingSizing of Nonconventional paperTesting of Sizing23. SOAP AND OTHER SURFACE ACTIVE AGENTSCommercial Soap ProductsCharacteristics of Soaps Saponified by different MethodsEffect of Different Factors on Physical Characteristics of Bar SoapsTypes of Commercial SoapFurface-Active Agents Other Than SoapClassification of SurfactintsList of SurfactantsAnionic SurfactantsNonionic SurfactantsAmpholytic SurfactantsApplicationsDetergentsWetting Agents24. PAINTS, VARNISHES, AND RELATED PRODUCTSMaterialsUnmodified Drying OilsModified Drying OilsResins and Copolymerizing MaterialsDryersThinnersPigmentsMiscellaneous EngredientsManufactured ProductsOil PaintsVarnishes Adn EnamelsWater-Dispersible Paints


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Printing InksManufacturing OperationsCooking of Varnishes and ResinsMixing and GrindingOther Mechanical Operations

25. MISCELLANEOUS OIL AND FAT PRODUCTSLinoleumOiled FabricsPutty and Other Sealing or Calking MaterialsRubberlike MaterialsCore OilsLubricating GreasesCutting OilsOil For Leather TreatmentTextile Lubricants and Softening AgentsPlasticizers

Illuminants and FuelsCosmetic And Pharmaceutical OilsTinning OilsHydraulic OilsInsecticides and FungicidesCommercial Stearic and Oleic AcidsOther Fatty AcidsMetal Soaps26. ISOCYANATE-MODIFIED DEHYDRATED CASTOR OILIntroductionMaterials and MethodsAnalytical MethodsPreparation of Urethane DerivativesFilm CharacteristicsResults and Discussion27. STYRENE COPOLYMERISATION OF ISOMERISED TOBACCOSEED (NICOTIANA TOBACUM) OIL AND ITS ALKYDExperimentalMaterials usedIsomerisationStyrenation of tobacco seed oilPreparation of styrenated alkydsPost-strenation ProcessResults and DiscussionIsomerisationStyrenationDrying CharacteristicsFlexibility and AdhesionScratch hardnessWater resistance


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Acid resistanceAlkali ResistanceConclusion28. MODIFIED MAROTI OIL (HYDNOCARPUS WIGHTIANA) FOR ALKYDSExperimental Techniques and Results

Formulation of alkydsEvaluation of film propertiesDiscussionConclusion29. IMPROVED ALKYDS WITH EPOXIDISED RUBBERSEED OILExperimental Techniques and ResultsFormulation of alkydsEvaluation of film propertiesDiscussionConcluion30. ALKYDS BASED ON BLOWN KARANJA OIL

ExperimetalFormulation of alkydsDiscussionConclusion31. THE PREVENTION OF GELATION DURING THEMALEINISATION OF DEHYDRATED CASTOR OILExperimentalPreparationMaleinisationWater solubilityResults and DiscussionReaction with AcrylonitrileReaction with acetic anhydride and phosphorus pentachloride32. UTILIZATION OF NONCONVENTIONAL OILSDiscussiohConclusion33. CASTOR-UREA RESINOUS OILExperimentalDiscussion of Results34. PALMDIESEL AS ALTERNATIVE RENEWABLE ENERGYChemistry of The ReactionLaboratory Evaluation of Alkyl Esters as Diesel SubstitutesStationary Engine testPrelminary Field TrialPorim vehiclesTaxisExhaustive Field TrialPilot PlantRecovery of Vitamin E & Other Minor Components from Methyl EstersFuture Development


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Reduction of pour points of methyl estersOne Step conversion of the processMore uses of GlycerolMethylesters as kerosene SubstituteOther uses of esters

ConclusionInclusion CompoundsCage (Clathrate) inclusion Compounds35. EXTRACTION OF FATS AND OILSPreparation of Animal MaterialPreparation of Oil SeedsHeat Treatment of Oil-bearing MaterialsRendering of Animal FatsCooking of Oil SeedsBatch PressingMechanical Expression of Oil

Continuous PressingLow-Pressure PressingCentrifugal ExpressionSolvent ExtractionApplicationRecovery of Oil from Fruit PulpsExtraction of Olive OilExtraction of Palm Oil36. REFINING AND BLEACHINGRefining & Bleaching MethodsEffect of Refining & Other Processing Treatment on specific ImpuritiesRefining LossesApplicationsDesliming or DegummingDegumming by hydrationPreparation of Commercial LecithinAcid RefiningRemoval of Break Material by Heat TreatmentAlkali RefiningReffining with Caustic SodaColor StandardsChemical Bleaching37. HYDROGENATIONImportance of HydrogenationHeat of reactionDiversity of Possible ReactionsSelectivity with Respect to Different classes fo GlyceridesNickel Alloy or Raney CatalystsHydrogenation EquipmentCharacteristics of hydrogenated Fats


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Hydrogenation of Shortening StocksHydrogenation of Margarine OilsHydrogenation of Hard Butter SubstitutesHydrogenation of Inedible Fats and Fatty Acidsremoval of Nickel From hydrogenated oils

Special hydrogenation ProcessesHydrogenation to Produce Fatty AlcoholsFatty Alcohols by Sodium ReductionConjugated HydrogenationHydrogenation of Nitriles to Produce Fatty AminesHydrogenation in Solvents38. DEODORIZATIONHistoricalNaturel of Deodorization ProcessGeneral Design FeaturesBatch Deodorization

Continuous Deodorization39. CUTTING OILManufacture of Soluble Cutting OilSoluble Cutting Oil by Sulphonated OilsManufactur fo Straight Cutting OilsProcessPlant Economics40. RICE BRAN OILIntroductionProcess of ManufacturePlant EconomicsManufacturers of Raw MaterialsManufacturers of fatty acids, fatty oils, drying oils & Its derivatives (UK)

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Sample Chapters(Following is an extract of the content from the book) Hide

Extraction of Fats and OilsThe separation of oils and fats from oil-bearing animal and vegetable materialsconstitutes a distinct and specialized branch of fat technology. The widely differingcharacteristics of fatty materials from diverse sources have given rise to extractionprocesses such as rendering, pressing, and solvent extraction. All extraction processes,however, have certain objects in common. These are, first, to obtain the fat or oiluninjured and as free as possible from undesirable impurities; second, to obtain the fat oroil in as high a yield as is consistent with the economy of the process; and third, toproduce and oil cake or residue of the greatest possible value.


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Fatty animal tissues consist largely of fat and water which may be separated from thesolid portions of the tissue and from each other with relative ease by one of the renderingprocesses. The extraction of vegetable oils is a more difficult matter. Vegetable materials,and in particular some of the oil seeds, contain a large proportion of solid materialassociated with the oil. Here, careful reduction of the material, followed by heat

treatment, and the application with the oil. Here, careful reduction of the material,followed by heat treatment, and the application of heavy pressure, is required to obtain anefficient separation of the oil from the solids.

Even after the most efficient pressing, an oil cake will retain an appreciable amount toabsorbed oil, usually amounting to 2.5 to 5% by weight. In the case of seed or othermaterials initially high in oil and low in solids content, the un-extracted residue willcontain only a small fraction of the total oil. However, in seeds of low oil content, forexample, soybeans, it may contain as much as 15% to 20% of the total oil. For theprocessing of low-soil seeds solvent extraction is particularly valuable, since it willreduce residual oil in the extracted seeds to less than 1%. The chief disadvantages of

solvent extraction are the high initial seeds to less than 1%. The chief disadvantages ofsolvent extraction are the high initial cost of the equipment and the fact that some oilseeds disintegrate under the influence of the solvent and consequently are difficult tohandle.

A number of more-or-less critical operations in oil milling are auxiliary to the actualexpression or extraction. Wherever possible it is desirable to decorticate oil seeds beforethe oil is removed in order both to increase the capacity of the extraction equipment andto avoid loss of oil through absorption by the hulls. The seeds must then be rolled, ground, or otherwise reduced to fine particles. After they are reduced, they must be givenheat treatment to make the walls of the oil cells permeable to the oil and to render the oilfree-flowing, except where solvent extraction is used; then heat treatment is not generallynecessary. In processing cottonseed, special attention must be given to the inactivation ofgossypol or other toxic constituents.

In extracting oil from oil seeds there are some major differences between commonAmerican and common European practice. They result from basic differences in thesupply of raw materials. Most American mills operate on domestic oil seeds, and they areusually located close to producing areas. Frequently only one type of oil seed isprocessed. The quality of the seed is generally high, with relatively little variation in seedcharacteristics through the processing season or from one season to another. Europeanmills, on the other hand, process imported raw materials almost exclusively, and eachmill must be prepared to handle a variety of oil seeds differing widely in quality andprocessing characteristics. As a result, American milling practice has become highlyspecialized, with the object in each case being to perform a specific operation with thehighest possible efficiency. In European mills it has been necessary to sacritice someoperating efficiency in favour of flexibility of operation. This accounts for the greater usein Europe of cage-type as opposed to open-type batch presses; and for the employment ofmultistage continuous pressing, as compared to single-stage high-pressure pressing inAmerica.


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Table 1.Average yield of oil from commercial processing of common oil seeds (Percent oil fromseed of normal moisture content)a

Babassu (kernels) 63 Perilla seed 37Castor beans 45 Roppyseed 40Coconut (copra) 63 Rapeseed 35Corn (germs) 45 Rice bran 14Cottonseed 16 Safflowerseed 28Flaxseed 34 Sesam seed 47Hempseed 24 Soybeans 18Kapok seed 20 Sunflowerseed 25Oiticica (kernels) 60 Teaseed 48Plam, African (kernels) 45 Tung 35Peanuts 35

The average yields of oil obtainable by commercial extraction methods from a number ofcommon oil seeds are summarized in Table 1. Certain comparative data on whole seedsand kernels are found in Table 2. For information on yields from fruit pulps and animalsources, reference should be made to the specific fats and oils in other portions of thischapter and in other chapters.

It is probable that the first methods of fat extraction were rendering procedures practicedby primitive man, following cooking techniques developed for the preparation of meatsfor food. The pressing of oil from olive pulp probably antedated the pressing of oil seeds,although seeds were processed by the Chinese and others at an early date usingmechanical presses operated by wedges or levers. On the other hand, the more efficienthydraulic operation of mechanical presses was not adopted until early in the nineteenthcentury. The continuous screw press is a modern development, and the solvent extractionof oil seeds on a large scale was not a reality until after World War I.

*Soyabeans are now being dehulled at many mills so as to produce a 50% proteinsoybean meal especially suitable where low fiber content is important in a feed.

The residues from the processing of oil seeds or animal tissues for fat are generally highin protein content and are in good demand as animal feedstuffs. They have a limited useas a source of human food (soybean or cottonseed flour), or as a source of industrialproteins (for example, for making glues). The residues from castor beans and tung nutsare toxic unless specially treated; hence they are used only as fertilizer, etc.

Mechanical PretreatmentPREPARATION OF ANIMAL MATERIALFatty animal materials, as compared with oil seeds and other vegetable materials, requirecomparatively little preparation prior to the rendering operation. Fatty stock destined for


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the production of neutral, low-temperature-rendered fats, such as oleo stock or neutrallard, is carefully trimmed and washed before it is charged to the rendering units. Ordinarystock, such as that used in making prime steam lard, is always washed and is lesscarefully trimmed.

In the larger establishments the stock to be rendered is sorted into different classes ofmaterial, partly to avoid mixing high-quality materials with those of low quality, andpartly because some stocks, such as those containing large bones, require more severerendering than others.

In either dry rendering or steam rendering, separation of the fat is more rapid if the fattystock is first cut into small pieces, although this operation is ordinarily omitted in steamrendering. Prolonged wet rendering under pressure will disintegrate even large bones orwhole carcasses, so that the preparation of stock for this process is not critical.

Rotary hashers, similar in principle to ordinary household food choppers, are used for the

reduction of stock which is free from bones. The degree of reduction is usually muchcoarser than that employed in the processing of oil seeds; the dimensions of the hashedpieces may be measured in large fractions of inches or even in inches. Most animalmaterials disintegrate quite readily. Whale blubber is particularly tough and requiresmore drastic treatment. Blubber presses, consisting of heavy corrugated rolls, are now inuse. Passage of large chunks of blubber through these rolls reduces them to semi fluidcondition and decreases the rendering time.

PREPARATION OF OIL SEEDSCleaning. The first step in the processing of oil seeds is cleaning to separate foreignmaterial. Sticks, stems, leaves, and similar trash are usually removed by means ofrevolving screens or reels. Sand or dirt is also removed by screening. Permanent orelectromagnets installed over a conveyor belt are used for the removal of tramp iron.Specialm "stoners" are employed for taking out heavy stones and mud balls from shelledpeanuts. As stated previously, the cleaning of oil seeds is preferably carried out before theseeds are placed in storage. Often, however, it is not, since adequate cleaning capacity iscostly.

Dehulling and Separation of Hulls. Wherever practicable, oil seeds are preferablydecorticated before they are extracted. The hulls of oil-bearing seeds are low in oilcontent, usually containing not more than about 1%, although contamination with kernelswill, of course, increase the oil content with resultant loss of available oil. If the hulls arenot removed from the seeds before the latter are extracted, they reduce the total yield ofoil by absorbing and retaining oil in the press cake and, in addition, reduce the capacity ofthe extraction equipment.

The hulling machines used for the decortication of medium-sized oil seeds with a flexibleseed coat, such as cottonseed, peanuts, and sunflowerseed, are of two principal types: barhullers and disk hullers.


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The rotating member of a bar huller is a cylinder equipped on its outer surface with anumber of slightly projecting, longitudinally placed, sharply ground, square-edged knivesor "bars." Opposed to the cylinder over an area corresponding to about one-third of itssurface is a concave member provided with similar projecting bars. The seeds are fedbetween the rotating cylinder and the concave member, and the hulls are split as the seeds

are caught, between the opposed cutting edges. The clearance between the cutting edgesmay be adjusted for seeds of different sizes.

The disk huller is more or less similar in principle to the bar huller except that the cuttingedges consist of grooves cut radially in the surfaces of two opposed and verticallymounted disks, one of which is stationary and the other rotating. The seeds are fed to thecenter of the disks and are discharged at their periphery by centrifugal force. With eithertype of huller the condition of the seed is somewhat critical. Wet seed are difficult to splitcleanly and may clog the huller, particularly if it is of the disk type. On the other hand, ifthe seeds are very dry, the kernels may disintegrate excessively.

Different seeds very considerably in the readiness with which they fall out of the splithulls. Peanuts, for example, are loose in the shell and separate readily. Cottonseed kernelsor "meats : are more adherent to the hull; consequently, the hulls are customarily passedthrough a hull beater to detach small meat particles after the first separation of hulls andmeats by screening. The separation systems used for cottonseed, peanuts, etc., consist ofvarious combinations of vibrating screens and pneumatic lifts. It is necessary not only toseparate the hulls from the meats but also to separate and recycle a certain proportion ofuncut seeds which escape the action of the huller. In the case of cottonseed the followingseparations are commonly carried out: (a) separation of large meat particles from hullsand uncut seed screening: (b) separation of hulls from uncut seed by an air lift:(c)separation of small meat particles from hulls by beating and screening; and (d)separation of hull particles from meats by air.

In practical mill operation, especially on cottonseeds, the greatest yield of oil is obtainedby nicely balancing the degree of separation attained. If an attempt is made to separatehulls from the meats too cleanly, there will be a loss of oil due to meats being carriedover into the hulls. If an excessive proportion of hulls is left in the kernels, there willlikewise be an undue loss of oils from absorption by the hulls. Under certain condition,there may be an appreciable loss of oil due to absorption by the hulls. Under certaincondition, there may be an appreciable loss of oil due to absorption by the hulls an thelatter come into contact with the oily meat particles during the separation operation. It isgenerally advisable to effect the separation of kernels and hulls as quickly as possibleafter the seeds are hulled, in order to avoid excessive contact between hulls and kernels orkenel particles.

Cottonseed are invariable delivered to the mills from the gins without removal of theircoating of short fibers or linters, and must be delinted before they are hulled. Delinteringmachines (known as "linter") are similar in principle and appearance to cotton gins,consisting essentially of a revolving assembly of closely spaced circular saws which pickthe lint from the seed. The fibers are removed from the saw teeth by a revolving


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cylindrical brush or by an air blast that suspends them in an air stream in which they areconveyed through pipes to collection equipment. The lint is not ordinary removed fromthe seed in a single operation but is taken off in two or three cuts. Each successive cut isof lower grade than the cut preceding it since increasing quantities of hull material areremoved by the saws as delinting proceeds and fiber length is decreased.

Previously soybeans were seldom decorticated before processing for oil (except wherethe meal was destined for human consumption) because of mechanical difficulties andbecause the hull constitutes but a small part of the seed and is relatively nonabsorbent.Today, dehulling is increasingly common. It is usually accomplished by first cracking thebeans on cracking rolls and then separating the hulls from the kernels in two stages :

Hulls are secreened from kernels and uncracked beans and aspirated at the end of the topdeck of a double-deck shaking screen. Uncracked beans are returned to the cracking rollswhile the kernels are put on a second deck of finer mesh screen at the end of which hullsare again aspirated. Fines are joined to the whole kernel flow.

Hulls which have been aspirated contain some kernel particles. Therefore, these aresubjected to an air separation using a gravity table to separate the light hulls from theheavier kernels. Depending on the degree of separation required, a "middling" fractionmay be taken and this broken down on another gravity table.A somewhat different system makes use of simultaneous grinding and aspiration todehull the beans and separate the hulls. In general, the choice of system, depends on theprocessor, who may use many modifications of general techniques for his purposes.

Small oil seeds, such as flaxseed, perilla, rapeseed, and sesame, are usually processedwithout decoration. In some cases it would be desirable to hull the small seeds if thiscould be done economically; but so far the process has been considered impracticable.Owen has reported a series of experiments in the dry decortication of flaxseed and othersmall oil seeds using an experimental machine of unspecified design. He concludes thathulling of linseed is impracticable because a large portion of the total oil is contained inthe separated hull, but he suggests that it might prove advantageous in the case of certainother small seeds, for example, hampseed.

The various palm kernels, such as oil palm or Africa palm kernels, babassu kernels, andcohune kernels, constitute a special class of oil seeds, since they are of relatively largesize and are surrounded by a particularly hard, thick shell. Because of the low cost oflabor in the producing regions, the large size of the nuts, and the refractory nature of theshells, these nuts are often cracked and the kernels separated by hand. The entireproduction of Brazilian babassu kernels, amounting in some seasons to 25,000 tons, hasin the past been separated in this manner.

In Africa, nuts of the oil palm, which are less thick-shelled than most of the Americanpalm nuts, are apparently hand-cracked to some extent; but on the plantations ofIndonesia and Malaysia they are usually machine-cracked. In one type of machine thenuts are fed to the center of a rotor provided with curved baffles, along which the nuts areflung out against a heavy steel housing and broken by impact Another type of machine is


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simply a special type of hammer mill. The rotor consists of a frame supporting four heavysteel paddles; the nuts are dropped into the path of the paddles and cracked by impact.

After the nuts are cracked they are dropped to rotary screens where some separation ofkernels and shells is obtained. A considerable proportion of shell fragment, however,

cannot be separated by screening. Owing to the high density of the shells, air separationlike that used on cottonseed and peanuts, etc., is likewise ineffective in producing afurther separation. Here are two methods in vogue for separating palm kernels from shellfragments of a size comparable to that of the kernels. The dry method takes advantage ofthe fact that the kernels are founded and roll easily, whereas the pieces of shell are flatand sharp edged, and hence do not roll as readily on an inclined surface.

Dry separators consist of inclined belts provided with sharp projections which movecontinuously upward. When a mixture of kernels and seeds is fed onto the surface of thebelt the kernels roll down the belt and are collected at the lower end, whereas thefragments of shell are caught on the projections and carried over the top of the belt into a

separate bin. Means must be provided for recycling of material after both the crackingand separating operations, since neither cracking nor separation is complete after onepassage of the material through the machines.

The alternative method of separation consists of floating the kernels from the more denseshells in brine solution. This method has the advantage of producing a clean separation ofkernels and shells, but the separated kernels must be dried before they can be stored orshipped.

The American palm nuts of the Attalea family, including the babassu and cohune, areexcessively thick-shelled and extremely difficult to decorticate by machinery. Thebabassu is particularly troublesome because it contains several kernels, each of which isenclosed in a separate cavity within the shell. Whereas the splitting of an oil palm nut ormost cohune nuts along a single plane of cleavage will usually free the kernel, the similarsplitting of a babassu nut may not release a single one of its four to eight kernels.

Recently, a number of different machines have been devised for cracking American palmnuts. The machines designed for round nuts of the coyol type have either been of thecentrifugal or hammer-mill design or have utilized the positive action of mechanically orhydraulically operated hammers striking against the nut as it is confined against astationary anvil member. Some of the machines designed for cohune or babassu nutsemploy chisel-like cutting edges which split the nut into a number of segments, like thoseof an orange. Other machines for cohune and babassu nuts employ the hammer-millprinciple. These machines break up the kernal rather badly, and thorogh drying of thekernels is relied upon to inhibit excessive enzyme action in the broken kernels duringshipment.

In the case of any variety of palm nut, adequate drying of the nuts prior to cracking ismandatory to ensure that the kernel will not adhere to the shell. Green or undried kernelsfill the shell cavity tightly and adhere very strongly. In Malaysia the general custom is


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said to be to expose oil palm kernels to the air in layers 4 to 5 feet deep in roofed shedsequipped with concrete floors. A month's drying under these conditions suffices forreasonably good cracking and separation, and 6 week's drying ensures good separation.Some factories use steam-heated drying rooms in which the nuts, contained on wire trays,are adequately dried in 3 days. Another effective drying method is to treat the nuts with

live steam in a revolving drum for 1 to 2 hours, after which they are air-dried for a fewhours. Because of their thicker shells, American palm nuts, such as the cohune and thebabassu, would be expected to dry more slowly. Aside from the fact that it is necessaryfor efficient decortication, thorough drying of the nuts will, of course, minimize thedanger of deterioration in the kernels from enzyme action.

Reduction of Oil Seeds. The extraction of oil from oil seeds, either by mechanicalexpression or by means of solvents, is facilitated by reduction of the seed to smallparticles.

Opinion is divided as to whether the grinding or rolling of oil seeds actually disrupts a

large proportion of the oil-bearing cells. The assumption of extensive cell breakage has inthe pas been based chiefly upon the fact that seed flakes yield a large fraction of "easilyextractable" oil upon treatment with solvents, and a smaller fraction (usually 10-30%) ofoil that is extracted with much greater difficulty. The former fraction was presumed tocome from broken cells. It has been shown, however, that seeds (soybeans) that arecracked rather than rolled, with a minimum of crushing, likewise yield a large fraction ofoil that is easily washed out with solvents. Further more, Woolrich and carpenter couldobserve little disruption of cells in rolled cottonseed flakes examined under themicroscope.

As an argument against extensive cell destruction they pointed out that the cells ofconttonseed are only 0.001-0.0015 inch in diameter, whereas the thickness of rolledcottonseed particles is not less than 0.005 inch. On the other hand, Shchepkina's ratherhigh estimates of the proportion or broken cells were made from a count of free aleuronegrains in flake samples.

In any event, it appears that many oil cells remain intact after even the most carefulreduction, and that the walls of these cells are made permeable to the oil only by theaction of heat and moisture in the cooking operation. However, the cell walls will bemore readily acted upon by heat and moisture if the seed particles are small.

Obviously, rolling seed or seed particles into thin flakes will facilitate solvent extractionboth from the disruptive effect of rolling and by reducing the distances that solvent andoil must diffuse in and out of the seed during the extraction process. Early work indicatedthat the rate-controlling factor in the solvent extraction of seed flakes was probably theinternal resistance of the flakes to the molecular diffusion of solvent and oil.

Hammer mills attrition mills, and other devices are sometimes used for the preliminaryreduction of large oil seeds, such as copra and palm or babassu kernels; but for the final


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reduction it is the almost invariable practice in the United States to use milling rolls.These are generally considered to be more economical to operate than other types of mill.Also, thin flakes to which oil seeds are reduced by smooth rolls are more satisfactory forhydraulic pressing than the irregularly shaped particles obtained by grinding. Flakingrolls are essential for preparing oil seeds for continous solvent extraction since no other

form of mill is capable of forming particles which are thin enough to extract readily yetlarge enough and coherent enough to form a mass through which the solvent will freelyflow.

A roll assembly commonly used for the reduction of cottonseed, flaxseed, and peanuts inthe mills of the southern United States consists of a series of five rolls placed one abovethe other. The seed is introduced by a feeding mechanism between the two top rolls. Itpasses back and forth between adjoining pairs of rolls as it travels from the top to thebottom of the assembly; hence it is rolled four times. Each roll supports the weight of allthe rolls above it, so that the seed particles are subjected to progressively increasingpressure as they pass from one pair of rolls to another. Although the lower rolls are

smoothy, the top roll is commonly corrugated to insure that the seed will be "nipped" asfast as they are fed to it. A popular five-high roll assembly consists of four upper rollseach 14 inches in diameter by 48 inches in width, and a bottom roll 16 inches by 48inches in size, operating at a peripheral speed of about 630 ft./min. This unit has a ratedcapacity of 80 short tons of cottonseed or 300 bushels of flaxseed in 24 hours. However,the actual capacity in any case depends upon the flake thickness that is obtained. Detaileddata on the capacity and efficiency of cottonseed flaking rolls have been published.

Cottonseeds are usually rolled to a thickness of between 0.0005 and 0.010 inch wheremechanical pressing is to be used. With solvent, flake thickness is seldom under 0.008 to0.010 inch. The repeated passage of the material through the rolls results in considerablebreaking up of the individual flakes but this is not particularly disadvantageous in thecase of seed which are to be mechanically expressed. Small oil seeds, such as flaxseedand sesame, are usually rolled in preparation for expression.

In the preparation of oil seeds for expression in expellers* or screw presses, theproduction of thin particles is not essential as for hydraulic pressing since heat isgenerated and seed particles are broken up by the intense shearing stresses developed inthe barrel of the expeller. Soybeans to be processed in expellers are usually cracked bycorrugated cracking rolls into particles averaging 10 to 16 mesh in size and are thenexpressed without rolling or further reduction. Plam kernels, copra, peanuts, etc., arehandled in expeller plants both with and without rolling. Cottonseed are usually rolledbefore expeller processing.

The rolls used for flaking soybeans or other oil seeds for solvent extraction are normallysomewhat different in design from those described above. Since large, coherent flakes aredesired, the flaking operation is commonly carried out by a singly passage of the wholeor cracked seeds through the rolls. Therefore only one pair of rolls is provided; the rollsare mounted side by side rather than being superimposed and are equipped with heavy


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springs to maintain the pressure of one roll against the other. Since the clearance betweenrolls of this type is adjustable, flakes of quite uniform thickness are produced.

A reasonable high moisture content is required in oil seeds which are to be formed intothin, coherent flakes. Very dry seeds do not flake well. For solvent extraction, cracked

soybeans are adjusted to a moisture content of 10-11% and flaked while still; hot andslightly plastic, that is, while at a temperature of 160-170 F. In some cases the crackedbeans are steamed for a short time prior to flaking.

Heat Teatment of Oil-Bearing MaterialsThe heat treatments given oil-bearing materials may be divided into two categoriesaccording to whether they are alone productive of oil or merely serve to facilitate thesubsequent expression of oil by mechanical means. The term "rendering" is generallyapplied to treatment designed to remove all or most of the fat from fatty animal tissues orother materials with a high ratio of fat to solid matter. The heat treatment applied to oilseeds and similar materials prior to pressing is more commonly termed "cooking". Some

methods of processing are a combination of rendering and cooking.

In the case of either rendering of cooing, the principal object of the heat treatment is thesame; that is, to coagulate the proteins in the walls of the fat-containing cells and makethe walls permeable to the flow of oil. The flow of oil from the oil-bearing material isalso assisted by the lowered viscosity of the oil at elevated temperatures. Since oil-containing materials are never completely dry, heat treatment is inevitably associatedwith various effects due to the presence of moisture, even when water is not added in theprocessing operation. Water must be present for the above-mentioned protein coagulationto take place. Anhydrous proteins do not readily coagulate or exhibit other evidences ofheat denaturation. In some cases water also assists in the displacement of oil from thesurfaces of solid materials through superior physiochemical affinity for the latter.

RENDERING OF ANIMAL FATSFatty animal tissues free from muscle or bone are usually 70-90% fat; the remainderconsists of water plus a small amount of connective tissue. The latter is made up largelyof proteins; hence, the residue from rendering ("tankage", "craklings", "stick", etc.) likethe residue from the processing of oil seeds, is essentially a protein concentrate which isused principally as an animal feed.

The product of highest fat content (92-95%) obtained in meat packing establishments isleaf fat from hogs. The internal fat from cattle used for the manufacture of oleo stockcontains 60-80% fat. A considerable amount of lard and tallow is obtained, however,from bone stock and other low-fat material, which may; not contain more than 10-15%fat. Under certain circumstances, whole carcasses of large animals may be rendered forinedible fat recovery and conversich of the residue to tankage.

Most of the fish oil produced comes from the rendering of whole small oily fished, suchas sardines and herring, which contain 10-20% oil. Whales, however, which give anaverage oil yield in the neighborhood of 30,000 pound per animal are trimmed of their


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fatty tissues or blubber, which contains about 70% fat and is rendered separately frombones or flesh.

Methods of rendering are dictated by the nature of the fatty stock, as well as thecharacteristics desired in the rendered fat and the rendering equipment available.

Dry Rendering. "Dry" rendering is one of the simpler methods of fat extraction. It isdistinguished from "wet" rendering in that the expulsion of fat is accompanied bydehydration of the fat and fatty tissues, so that the latter are essentially dry at the end ofthe operation. The drying of bacon, to cite a familiar example, is essentially a dry-rendering process.

Dry rendering is normally carried out in horizontal steam-jacketed tanks with a largecharging opening in the center of the tip and an agitator. The agitator has paddlesattached by arms to a horizontal shaft. After the charge (5,000 to 10,000 pounds) is driedto the desired moisture level, the contents are discharged into a steel box equipped with a

perforated liner and all possible free liquid drained off. The residue is pressed, and the fatobtained is combined with the drained fat. After settling, centrifuging, or filtering, it isready for market. The residue is ground as a protein supplement for animal and poultryfeed.

The cooking or drying operation may be carried out at atmospheric, superatmospheric, orreduced pressures. Best yields are obtained under vacuum, but most plants operate atatmospheric pressure. Recent development in cooking includes increased agitation (34 to40 r.p.m. versus 15 to 20 formerly), permitting a decrease for animal and poultry feed.

The cooking or drying operation may be carried out at atmospheric, superatmospheric, orreduced pressures. Best yields are obtained under vacuum, but most plants operate atatmospheric pressure. Recent development in cooking includes increased agitation (34 to40 r.p.m. versus 15 to 20 fomerly), permitting a decrease in cooking time of about 25%.

Dry rendering is preferred for inedible products where flavor and odor are secondary andthe production of large quantities of high quality residue is important.

Wet Rendering. Wet rendering is used for edible products where color, flavor, andkeeping qualities are of prime importance and the relative percentage of residue is mall. Itis carried out in the presence of a large amount of water. Separated fat was formerlyremoved by skimming, but centrifugal methods are widespread today. There are twovarieties of wet rendering: low-temperature, which is conduced at temperatures up to theboiling point of water, and high-temperature or steam rendering, which is carried outunder pressure in closed vessels.

Most of the animal fat produced in the United States is rendered by the steam process.The lard produced by this method of rendering is known as "prime steam lard". Inaddition to lard, tallow and whale oil are also usually steam rendered.


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The apparatus used in United States packing houses is a vertical cylindrical steelautoclave or digester with a cone bottom, designed for a steam pressure of 40 to 60pounds per square inch and a correspondingly high temperature. The vessel is filled withthe fatty material plus a small amount of water, and steam is admitted to boil the waterand displace the air. The vessel is then closed except for a small vent, and the injection of

steam is continued until the operating temperature and pressure are attained; thendigestion is continued for a variable time depending upon the temperature and also thenature of the charge. The usual digestion time is 4 to 6 hours. Under the influence of thehigh temperature employed, the fatty materials in the digester disintegrate to some extent;there is very efficient separation of the fat, which rises to the top of the vessel, leaving alayer of solids (tankage), and "stick water" in the bottom. Pressure is then slowelyrelieved, and the fat-water interface is adjusted to the level of a draw-off cock on the sideof the vessel. The fat is drawn off and purified from traces of water and solid material bysettling or occasionally by centrifuging. Eventually it may be filtered.

In the steam rendering of high-fat stock, 99.5% or more of the fat in the raw material is

ordinarily recovered. The fat that is not recovered consists of a small residue in thetankage plus a very small amount which remains in the "stick water". The usual packinghouse "killing" and "cutting" fats yield about 80% and 70% lard, respectively, plus 2 to3% each of dry tankage and dry "stick" or solid residue from the evaporation or "stickwater". The dry tankage and stick will ordinarily contain about 10 to 12% and 1.5% to2% of fat, respectively. Both are high in protein content; tankage from good stock mayanalyze as high as 70 to 72% protein, and stick may be as high as 90% or more.

The advantages of steam rendering are that an efficient recovery of fat is obtained inrelatively simple equipment and that it is adaptable to a wide variety of material. There islittle tendency for proteins, etc., to dissolve or disperse in the fat in the presence of water;hence the fatty stock may contain a large proportion of nonfatty tissue. Bony stock can behandled by this process since it is effectively disintegrated by prolonged treatment withsteam under an elevated pressure.

Steam rendering is less rapid and less efficient than dry rendering from the standpoint ofheat consumption, however, and a large amount of water must be evaporated in order torecover the non-fatty residue in a concentrated from. Some hydrolysis of fat occursduring steam rendering; the free fatty acids content of prime steam lard is seldom lessthan about 0.35%. At 47 pounds pressure development of free fatty acids is at the rate ofabout 0.06% per hour. The acidity in any case depends upon the rendering time andtemperature and the storage temperature and duration of storage of the fatty stock beforeit is processed. By careful scheduling of operations, killing fats may be renderedreasonably soon after the animals are slaughtered, but carcasses are chilled to 32-36Fbefore cutting fats are available. The stability of lard towards oxidation bears no relationto the acidity and appears to depend principally upon processing and handling subsequentto rendering.

One of the major recent developments in rendering has been the discovery thatantioxidants added before rendering greatly enhance the stability of the fat produced.


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Sims and Hilfman studied the stabilization of lard and edible beef fats during pressuresteam rendering. Antioxidants tested included butylated hydroxyanisole (BHA), butylatedhydroxytoluene (BHT), propyl gallate and citric acid combinations, and a mixture ofBHA and BHT. Poorer results were obtained with the mixtures in propylene glycol.

There are several modifications of continuous wet rendering operations in which attemptsare made to obtain a better product and a better protein residue than the usual pressuretank products. These include.

KINGAN PROCESS. This process is based on the release of oil from tissue throughcomminution to subcellular dimensions. Raw material is finely ground, pumped throughan appropriate heat exchanger, and reground in a hammer mill, and the fat is thenseparated from the protein and waste by a special type of centrifuge.TITAN EXPULSION SYSTEM. The fat stock is quickly minced and rendered in acombined mixer-boiler apparatus ("Expulsor"). It is then strained (to remove tissue,which is subsequently pressed) and the strained emulsion pumped to continuous three-

phase separators where a low-moisture clarified oil is drawn off and separated sludge isintermittently discharged.DELAVAL CENTRIFLOW PROCESS. Cell rupture is accomplished by mechanicaldisintegration (first minimizing temperature as required) in a specially designeddisintegrator. Then cracklings are removed from the fat mass by a "desludger" centrifuge,after which the liquid phase is heated, deodorized, and centrifuged to produce purified oiland glue water.SHARPLES PROCESS. This is based on the mechanical rupturing of the fat tissue,followed by two-stage centrifugal separation. A "Super-D-Canter" separated the proteintissue from the liquid fat and discharges it as a dry meaty solid. A second centrifugecalled an "Autojector Clarifier" removes protein and water from the fat, intermittentlydischarging sludge. By suitable low temperature (115 to 120F.) a non-coagulated proteinmaterial is produced as one of the products, it is claimed, and this product appears to havepossibilities as an edible meat product.IMPULSE RENDERING. This process is used mainly for preparing and defatting bonesfor glue. Fat stock, especially crushed bones, is continuously disintegrated in a high-speed hammer mill under an excess of flowing cold water. The intense impact sets the fatfree. The discharge from the mill is allowed to settle in a cold water tank from which thefat is continuously skimmed off. The ground bone is continuously removed from thebottom and transferred to another tank containing hot waster (70-95F), where more fat isseparated. It is claimed that better-quality fat and higher protein residue are obtained bythis process.The production of marine oils is rather similar to animal fat rendering. It varies with thetype of fish processed and whether vitamin A and D oils or high-quality fish meal is theprime objective. With the synthetic production of vitamins D2 and D3 as well as vitaminA, the current trend is to fish meal and dissolving the connective tissue.

Deatherage has described in detail laboratory and pilot plant experiments on the alkalirendering of lard and beef fats. The best results are obtained when the fat is digested at85-95C for 45 minutes to an hour with a 1.75% sodium hydroxide solution. After


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digestion is complete, the fat is sepatrated from the aqueous liquid, which contains asmall amount of undigested solids, by centriguging, and washed, first with 2-5% saltsolution, and then with water. Fat recovery is equivalent to or better than that obtained bysteam rendering without significant hydrolysis or darkening of the fat or production ofthe typical cooked flavor of steam lard. The process is best adapted to reasonably fresh

fat; stocks in which any considerable amount of hydrolysis has occurred are difficult toprocess because of the excessive formation of soap in the aqueous phase. Soap is derivedonly from free fatty acids in the fat; under the mild conditions of the digestion, thereappears to be no appreciable saponification of neutral fat. The fat is, of course, alkali-refined as it is rendered; hence it is produced substantially free of acidity. A typical lardhas a free acids content of 0.01% and a Lovibond color of 2 yellow and 0.3 red.

Rendering slaughterhouse waste by ammonia plus ammonium diacid phosphate underpressure for peptonization and separation into aqueous and fat phases has been patented.

A recent publication reports reduced "fruitiness" and free fatty acids in olive oil from

adding alkaline materials to olive pulp during grinding or working. Also the manufactureof a good quality olive oil has been claimed by drying olive pomace to 5% moisture,mixing with soda ash, and extracting with carbon disulfide.

Alkali rendering has been found better than steam, water, or acid digestion for recoveringvitamin A from fish livers with an oil content of 30% and upwards. Partial removal ofantioxidants does not impair the stability of the vitamin.

The use of proteolytic enzymes in rendering is described in a number of patents. It doesnot however, appear to have been used commercially, expect perhaps in the recovery offish liver oils. The patent of Parfenjev covers the digestion of fish livers with pepsin at alow pH and a low temperature. The process of Keil for the recovery of lard or otheranimal fats involves digestion of the fatty stock with a proteolytic enzyme of vegetableorigin; for example, 0.005-0.020% papain at a pH of 6.0-7.5, followed by heating to 140-185F to separate the fat. Halmbacher has patented the use of an enzyme, such as papainor ficin, with a cysteine activator, to decrease digestion time while increasing yield. Otherpublications deal with treatment of eggs with papain, fish rendering (40), and renderingof coconut meats.

COOKING OF OIL SEEDSGeneral Considerations. It is university recognized that oil seeds yield their oil morereadily to mechanical expression after cooking, but a complete explanation of why this isso is lacking. It is certain that the changes brought about by cooking are complex and thatthey are both chemical and physicochemical in nature.

The oil droplets in a cottonseed or similar oil seed are almost uctramicroscopic in sizeand are distributed throughout the seed. One effect of cooking is to cause these very smalldroplets to coalesce into drops large enough to flow from the seed. An important factor inthis phase of the process is the heat denaturation of proteins and similar substances.Before the proteins become coagulated through denaturation, the oil droplets are virtually


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in the form of an emulsion. Coagulatio causes the emulsion to break, after which thereremains only the problem of separating gross droplets of oil from the solid material in theseed. Since the surface of the seed particles is highly extended, surface activity figuresprominently in the displacement of the oil. Cooking, in turn, has a profound influenceupon the surface activity of the material. The primary objects of the cooking process may,

therefore, be summarized as follows : (a) to coagulate the proteins in the seed causingcoalescence of oil droplets and making the seed permeable to the flow of oil; and (b) todecrease the affinity of the oil for the solid surfaces of the seed so that the best possibleyield of oil may be obtained when the seed are subsequently pressed.

Important secondary effects of cooking are drying of the seeds to give the seed mass theproper plasticity for efficient pressing insolubilization of phosphatides and possibly otherundesirable impurities, destruction of molds and bacteria, increase of the fluidity of theoil through increase in temperature, and, in the case of cottonseed, detoxification ofgossypol or related substances.

One factor that obviously effects the affinity between the seed and the oil and isamenable to control in the cooking operation is the moisture content of the seed. Very dryseeds cannot be efficiently freed of their oil. However, it is impossible to say just howmoisture inhibits wetting between the seed and the oil. It may be that the cooking processproduces a film of adsorbed liquid water on the seed surfaces which displaces the oil. Onthe other hand, the water may be in a more nearly "bound" state, and its presence in theseed in this condition may serve to make the seed surface relatively lipophobic. Theoptimum moisture of cooked seed varies widely according to the variety of the seed andthe method to be used for expression. On cottonseed, for example, 5 to 6% moisture isbest for hydraulic pressing, whereas about 3% is optimum for expellers or screw presses;this level needs to be closely controlled for best results. At moistures of 4% and higher,excessive amounts of oil are left in the cake. Soybeans are ordinarily dried to 2 to 3%moisture before pressing in expellers; copra and sesame seed require moistures of about2%.

Many substances in oil seeds are surface active, such as phosphatides and free fatty acids,and the degree to which they are present or become active during cooking doubtlessinfluences the tendency of the seed to adsorb and retain oil. It is generally observed thatdamaged oil seeds give lower yields of oil than undamaged seeds of equivalent oilcontent. The tendency of damaged seed to retain oil tenaciously is probably due to theirhigh content of free fatty acids or other surface-active agents.

Effect on Quality of Oil and Oil-Cake. In addition to its effect upon the yield of oil, themethod of cooking also markedly determines the quality of both the oil and the oil-cake.Cooking is particularly important in its relation to the refining loss of the oil. A large partof the oil lost in caustic refining consists of neutral oil, which is emulsified in the foots.Certain surface-active agents naturally present in the oil favor this emulsification; othersappear to inhibit it. The relative proportions of the two classes of substances in the oildepend to a great extent upon the operation of the cooker. There is little publishedinformation on the identity of the surface-active agents in crude oils, but is appears that


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the substances. The presence of gossypol in cottonseed oil is generally assumed tocontribute to the production of hard foots and a low refining loss. However, in mill-scaleexperiments by Wamble and Haris conducted at five different screw-press mills, it wasconcluded that there was no apparent relation between the gossypol content of the crudeoil and the refining loss or refined color.

Normal cooking variations have little effect on oil color or refining loss, although withwidely varying cooking conditions considerable differences are noted. Thus, Eavesshowed that oils prepared by solvent extraction from raw, tempered, or cookedcottonseed flakes varied in yield of crude oil but that the yield of neutral oil was virtuallyunaffected. Crude oil from raw flakes was highest in impurities and lowest in neutral oil,crude from tempered flakes was lower in impurities and higher in neutral oil, and crudefrom cooked flakes was outstandingly low-refining-loss oil. That is, unless oil penaltiesare sufficient to counteract any change in crude oil yield, it may be to the processor'sadvantage to avoid partially refining the oil during preparation for extraction.

King have studied the effect of pH during cooking of cottonseed on the properties of themeals and oils. They concluded that oils made from meats cooked at low pH were high ingossypol and were subject to color reversion during storage, while oil from meats cookedat high pH levels had a lower refining loss, were low in gossypol, and were not subject tocolor reversion on storage.

In good cooking practice flaked cottonseed meats are brought to approximately 12 to15% moisture by the time they are in the tip kettle of the cooker. There the temperature isincreased rapidly to 190F or higher in order to inactivate the enzyme systems andprevent free fatty acid rise during cooking. Heating should be continued in the presenceof not less than 12% moisture until the temperature reaches about 220F. After this theobject is to reduce the moisture content to a suitable value for efficient pressing. Thisnormally requires temperatures from 240 to 270F, depending upon the amount ofventing used. An average final temperature is probably 260F.

Overcooking of oil seeds has been recognized as undesirable for some time since it mayproduce abnormally dark oil and cake. There is also evidence that prolonged or drasticcooking tends to be injurious to the nutritive properties of the cake. With cottonseed, forexample, it has been shown that increasing maximum cooker temperature or cookingtime decreases the feed efficiency for chicks and the relative protein efficiency for rats.Likewise, soybean meal has been shown to lose nutritive value for chicks as heating timeis increased.

On the other hand, the nutritive value of soybean meal is definitely improved bymoderate cooking. This is due to the coincident inactivation of specific heat-labile factors(trypsin inhibitor, hemagglutinin, saponin, goitrogenic factor, anticoagulant factor,diuretic principle, and lipoxidase). This subject has been recently summarized by Liener.

To improve their palatability and nutritive value, solvent-extracted soybean flakesintended for animal feeding are invariably toasted before they are shipped from the


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extraction plant. Until fairly recently this was done by adding moisture and cooking in aconventional "stack" cooker after the solvent was removed. With improveddesolventizing techniques, desolventizing and toasting are largely accomplishedsimultaneously by injecting live steam into the solvent-laden flakes as they leave theextractor them steam condenses on the cooler flakes, thus furnishing heat to boil off

solvent while at the same time adding moisture. Thus by the time all of the solvent isremoved there has been sufficient moist heat to boil off solvent while at the same timeadding moisture. Thus by the time all of the solvent is removed there has been sufficientmoist heat treatment largely to inactive the heat-labile anitinutritional factors mentionedabove. If the oil seed residue is destined for industrial protein use, this type ofdesolventizing is avoided and a quick heat treatment just sufficient to remove the solventis carried out, often using superheated solvent vapor or reduced pressure.

One of the prime purposes of cooking cottonseed is to bring about destruction ordeactivation of a principal toxic to certain animals (particularly swine and poultry) which

has in the past been generally identified as the complex polyphenolic compound,gossypol. Boatner and coworkers have shown that gossypol is associated in the seed withseveral related compounds and that one or more of these may be actually responsible forthe bulk of the observed toxicity, in as much as separated whole pigment glands are muchmore toxic than purified gossypol. At the present time, most people attribute all thetoxicity of cottonseed to free gossypol. At the present time, most people attribute all thetoxicity of cottonseed to free gossypol. At the present time, most people attribute all thetoxicity of cottonseed to free gossypol, possibly because no one has seen a low free-gossypol meal that was toxic. On the other hand, there have been numerous cases ofnontoxic meals containing levels of free gossypol above that normally considered toxic.A partial explanation for this may be the method of analysis for gossypol. Besides thenumber of other materials closely resembling gossypol in chemical nature, it has nowbeen established that gossypol that is chemically combined may be partially liberated inthe analytical procedure, giving abnormally high free-gossypol figures. Thus a specialmethod is now offical for aniline-treated cottonseed meal.

The toxic principle, whatever it may be, is contained in the cottonseed pigment glands,from which it may be extracted by either, acetone, butanol, and other polar solvents.Hexane and similar non-polar solvents will not extract it from the intact pigment glands,but if these glands are ruptured by moisture, wet heat, or polar solvent, the liberated"gossypol" is readily extracted. The toxic principle is quite stable to dry heat.

Lyman and coworkers, who have made a special study of the cooking of cottonseed inrelation to detoxification recommend for hydraulic pressing that meats be brought to amoisture content of at least 14.5% before cooking, that the cooking period be at least 90minutes, and that the final temperature be not less than 115C (239 F). A review of thework of many other investigators, however, indicates that for expeller processing theinitial moisture content may be lowered somewhat (to about 12%) and the cooking timegreatly reduced. In this connection it is important to bear in mind that the term "cooking"usually is used to cover wet cooking plus a drying to moisture levels around 3%.


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Actually, these are two distinct processes, as Dunning has pointed out, and after the wet-cooking step is completed, subsequent drying may be done instantaneously (by flashing)or very slowly. In normal practice, however, both processes are accomplished in a stackcooker where these is a rather gradual reduction in moisture content and, thus, a gradualtransition from cooking to drying. Final cooking temperature is thus considerably

dependent upon the amount of venting or aeration of the cooked flakes. For example, afinal cooking temperature is thus considerably dependent upon the amount of venting oraeration of the cooked flakes. For example, a final cooking temperature of 240F or260F will yield the same final moisture content if adequate venting is used with thelower temperature.

Cooking for Hydraulic and Continuous Pressing. The cooking of oil seeds is usuallycarried out in "stack cooker". These consist of a series of four to eight closed,superimposed, cylindrical steel kettles each usually 72 to 100 inches in diameter and 1.5to 2.5 high. Each kettle is normally jacketed for steam heating on the bottom (andsometimes on the sides), and is equipped with a sweep type stirrer mounted close to the

bottom and operated by a common shaft extending through the entire series of kettles.There is an automatically operated gate in the bottom of all but the last kettle fordischarging the contents to the kettle below; the bottom kettle feeds into a cake former orcontinuous press. The top kettle is provided with spray jets for the addition of moisture tothe seed, and each of the lower kettle is provided with an exhaust pipe with natural orforced draft for the removal of moisture. Thus it is possible to control the moisture of thecooking seed, not only with respect to final moisture content, but also at each stage of theoperation.

In practice, the rolled meats are delivered at a constant rate to the top kettle by means of aconveyor. After a predetermined period of cooking in that kettle, the charge of meats isautomatically dropped to the kettle below so that there is a continuous progression ofmeats downward through the cooker. The gates which govern the flow of meats from onkettle to another are normally opened and closed automatically by a mechanism whichengages the meats at a specific level in each kettle. Thus, the time that the meats chargeremains in each kettle is determined by the meats levels for which the kettles are set. An85 inch, five-high cooker, a common size, has a rated capacity of about 90 tons ofcottonseed (calculated upon the basis of the whole seed per 24 hours.

Steam pressure on the upper stacks of a stack cooker is usually maintained at a relativelyhigh value, for example, 70 to 90 pounds per square inch, in order to provide quickheating. On the lower stacks it is usually reduced somewhat, since there it is onlynecessary to maintain the heated meats at cooking temperature. Cottonseed meats areusually kept in the cooker for 30 to 120 minutes and leave at a temperature of 230-270F.Seed of good quality are normally cooked longer than poor seed, which tend to darken onprolonged cooking. Peanuts are often cooked for a shorter period.

In continuous operation of a stack cooker, material first in is not always first out. This hasbeen noted by Alderks and can be easily demonstrated by the use of added corn kernels,salted flakes, dyed flakes, etc. So-called "cooking time" represents an average cooking


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time, with some material remaining in the cooker much longer and some material only afraction of the average time. However, this does not appear to affect efficient mechanicalpressing adversely.

Oil seeds are usually moistened before cooking, or during the early stages of cooking,

unless they are initially fairly high in moisture, and their moisture content is then reducedin the cooker. An initial moisture content of 9 to 14% is common in the top kettle of thecooker. This stays relatively constant in the top two to four kettles where the actual"cooking" takes place. In the bottom kettles drying is the objective with increasedtemperatures and venting commonly employed. The final moisture content depends onthe material processed and on whether cooking is to be followed by hydraulic pressing orexpeller or screw pressing. For the former, 5 to 6% is used for cottonseed; for the latter, adryer product, around 3% moisture, is preferred.

Pressure cooking appeared promising at one time and equipment was installed in severalmills. Today, however, this type of cooking is not believed to be in use in any

commercial installation in this country.

Another specialized type of cooking, the Skipin process, was developed in Russia abouttwenty-five years ago but has had no acceptance in this country, where quality andefficiency standards are apparently much higher.

It should be noted that although cooking in a stack cooker has been stressed here, it isalso possible to accomplish the same objective using horizontal jacketed tubes("conditioners") through which the material is conveyed by suitable means. In general,these are more commonly used in conjunction with some stack cooking rather than as asubstitute for the latter.

Mechanical Expression of OilBATCH PRESSINGIn recent years increased mechanization and higher labor costs have made hydraulicpressing of oil seeds uneconomical in practically all cases. Today there is no appreciablevolume of soybeans hydraulically pressed, and even with cottonseed, where efficiency isbetter, volume is rapidly decreasing to a point where the end is in sight. Pressing of otheroil seeds appears doomed to the same fate.

The oldest method of oil extraction comprises the application of pressure to batches ofthe oil-bearing material confined in bags, cloths, cages, or other suitable devices.

Levers, wedges, screws, etc., have been used us a means of applying pressure in the moreprimitive styles of presses, but modern presses are almost invariably actuated by ahydraulic system. Thus the term "hydraulic pressing" is often used in reference to batchpressing in general. There is a limited use of mechanically operated presses for specialpurposes where only a relatively light pressure is required, as in the pressing of partiallysolidified oleo stock or lard to yield oleo oil or lard oil.


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Batch presses may be divided into two main classes: the "open" type, which requires theoily material to be confined in press cloths; and the "closed" type, which dispenses withpress cloths and confines the material in some species of cage. Open-type presses may besubdivided into plate presses and box presses, and closed types may be subdivided into

plate pressure and box presses, and closed types may be classified as pot presses or cagepresses.

The completeness with which the oil is recovered by mechanical expression is influencedby a number of factors related to the affinity of the oil for solid material in the seed.These include the moisture content, the method of cooking, and the chemical compositionof the seed, damaged seed generally retain oil more tenaciously than seed of good quality.With a given lot of seed, cooked and ready for pressing, the oil yield will depend uponthe rate at which pressure is applied, the maximum pressure attained, the time allowed foroil drainage at full pressure, and the temperature or the viscosity of the oil.

Attempts have been made to establish a correlation between oil recovery from differentseeds and such factors as pressure, pressing time, and temperature or viscosity. Koo andBaskerville et al. proposed empirical equations designed to permit a calculation of thefraction of oil extracted from seed from data on the pressing time, pressure on the cake,viscosity of the oil, etc. all other factors being assumed constant. Later work, however,indicated that factors are involved, all of which are not mutually independent, so that itmay not be possible to develop single equation which will correlate all the processingvariables.

Hickox has summarized four years of work in this connection at the EngineeringExperiment Station of the University of Tennessee, Including data from some millscaletests. He concludes that for hydraulic pressing of cottonseed:

The hull content of meats to be pressed should be kept as low as possible since increasedhulls lower extraction efficiency and press capacity;Pressure should be applied slowly at first, more slowly than is customary;The total pressure on the cake need not be increased over 2000 pound per square inchunless the final cake thickness is over 1 inch. For thin cakes, increasing the pressure hadno effect on the residual oil;The cake should be kept as thin as economical considerations and throughout of the millwill permit.The moisture content of the cake should be controlled carefully (that is, wihin a fewtenths of 1%) in order to obtain minimum residual oil;Since the top and bottom cakes in the press are cooler than the middle cakes, it isdesirable to raise their temperature by appropriate means in order to obtain maximumextraction efficiency; andPreferably, pressing should be carried out at temperature of 205F, about 30 higher thantypical mill operation.Open-Type Presses. The frame of an open or Anglo-American press consists of fourheavy, vertical steel columns fastened at the top and bottom to heavy end blocks. Within


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the open cage formed by the columns, and suspended from the top of the press, are aseries of horizontal steel plates. These plates closely fill the space enclosed by thecolumns. They are equally spaced at intervals the entire assembly to become compressedin the pressing operation. Below the plate assembly and attached to a ram operated frombelow is a heavier bottom plate. The material to be pressed is formed into rectangular

cakes which are placed between the various suspended plates. Raising the ramcompresses the series of cakes and causes the oil to fall into a drip pan resting upon thebottom block. The stress created by the application of pressure is directed against the topblock and is transland into longitudinal stress upon the four columns.

In ordinary plate presses the oil seed flakes are completely wrapped in press cloths andplaced between the plates without the use of accessory devices to restrain the cake massas it is pressed. The surfaces of the plates, however, are usually either corrugated orcovered with hair mats to assist in the drainage of the oil and to overcome cake cree page.Box presses are provided with a special boxlike arrangement which encloses the cake on

its two long sides and simplifies the wrapping of the cake. The complete press boxincludes a corrugated drainage rack, a perforated and corrugated steel drainage mat whichrests upon the drainage rack and underneath the cake, and steel "angles" which projectfrom the underside of each plate to from the sides of the box enclosing the cake below.With this arrangement, if is only necessary for the press cloth to enclose the cake on thetop, bottom, and ends. Thus folding of the press cloth in two directions is avoided, andvery heavy, durable cloths may be used. Standard size press boxes are about 2 inchesdeep, 35 inches long, 14 inches wide at the back, and 14 inches wide at the front, beingslightly widened from back to front to facilitate insertion and removal of the cake.Presses are usually constructed with either 15 or 16 boxes. Plate presses of an equivalentsize have 24 plates and hence have a greater capacity than box presses.

Presses similar to those described above are generally provided with a 16-inch ramoperating at a pressure of 4000 to 4500 pounds per square inch; hence to pressure on thecake is between 1650 and 1850 pounds per square inch. It is important to build uppressure upon the cakes gradually. In order to conduct the initial state of compressionmore rapidly than the later stages, the hydraulic system operating the presses is providedwith automatic valves which delivers oil at 500 pounds pressure to the ram until anequivalent pressure is built up on the cake, and thereafter delivers the maximum pressureof about 4000 pounds. The time allowed for drainage of the oil after the maximumpressure is reached is somewhat variable among deferent mill operators. However, atypical press cycle is as follows: for charging the press, 2 minutes; for attainingmaximum pressure, 6 minutes; drainage time, 26 minutes; for discharging the press, 2minutes; total, 26 minutes. The capacity of a 15-box press operated under theseconditions is approximately 11 short tons of whole cottonseed or whole peanuts per 24hours.


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According to Baskerville and Wamble the average press cycle in mills processingcottonseed in the Unites States is probably 30 minutes or less; their calculations indicatethat the economically optimum cycle is approximately 50% longer.

An essential accessory to the operation of either plate or box presses is a cake former for

automatically delivering a proper quantity of flakes from the cooker and forming theflakes into a cake of the proper size and shape within the press cloth. Cake formers aredesigned to press the flakes into a coherent mass without the application of sufficientpressure to start the oil from them. They are hydraulically operated. Mechanicallyoperated cake strippers are also provided for removing the somewhat adherent pressclothes from the spent press cake. Charging and discharging the presses is carried outentirely by hand, however. An operator is also required for both the cake former and thecake stripper, as neither is fully automatic.

The edges of the cake coming from an open-type press are soft and higher in oil contentthan the remainder of the cake. Consequently, it is the usual practice to slice or beat off

these edges in a mechanical cake trimmer and rework the trimmings through the presses.

Plate presses are usually preferred for flaxseed, whereas box presses are standardequipment in cottonseed or peanut mills. The press cloths used with box presses arewoven from human hair, camels; hair, or nylon. A wide variety of materials are used forthe cloths used in plate presses, including cotton, wool, and hair.

Closed-Type Presses. Cage presses confine the oil-containing materials within a strongperforated steel cage during the pressing operation, and thus largely dispense with the usefor press cloths. They may be operated at higher pressures than are practicable with openpresses. They are particularly suitable for the expression of copra, palm kernels, and otheroil seeds which are high in oil content and low in fiber and hence are inclined to flow andburst the press cloths of open presses. Castor beans or other seeds which it is desired toprocess without heat treatment can be pressed satisfactorily only in presses of this type asvery high pressures are required to extract the oil efficiently from cold seeds. They aredesirable for mills that process many varieties of oil seeds because they can be used onpractically any oil seed or other oily material.

Cages for this type of press are built in both round and square forms. They are usuallymade up from a number of closely spaced steel bars or slotted steel plates, supportedinside a heavy frame or ringed with heavy steel bands. The channels through which theoil escapes increase in size from the interior of the cage outward to minimum anytendency for them, to become clogged with solid particles. The cages are operated in avertical position in a frame similar to that of the Anglo-American press. Oil is expressedfrom the charge by forcing a closely fitting head up into the cage from below by means ofa hydraulically operated ram. The upper end of the cage may be closed solidly; thenpressure is allied only to one end of the charge. Alternately, the cage may float betweenthe lower ram and an opposed head entering from above. In the latter case, pressure isapplied to both ends of the seed mass. Cage presses are designed to attain pressures of6000 pounds per square inch or more.


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Since there is a marked tendency for the oil flow in the compressed cake to belongitudinal rather than radial, the cage cannot be packed solidly with the oil seed butmust be charged with layers of seed separated by drainage plates and press cloths.

Auxiliary equipment is required for filling the cages and discharging the cake. This, andthe rather elaborate and heavy design of the cages, makes the initial cost of this type ofpressing equipment relatively high. In large installations the cages are usually maderemovable from the presses, and filling and discharging presses are provided, in additionto a number of finishing presses. A cage carriage is provided for transferring the heavycages from one press to another.

The pot press is a special form of cage press used for the extraction of cocoa butter orother fats which are solid at ordinary room temperature. In this press the cage is replacedby a series of short, superimposed, steam-heated cylinder sections or "pots". The walls of

the pots are solid, and drainage takes place through perforated plated and filter mats inthe bottom of each section. Pot presses are usually designed for pressures intermediatebetween those employed in open presses and cage presses, although they can be built forvirtually any desired pressure. The advantages of pot presses are that they can be heatedand that they can handle very soft, non-fibreus material, such as fruit pulp, at highpressures without forcing large quantities of solid material into the oil. Their capacity issmall, however, in relation to their size and cost, and they require more hand labor tooperate than other types of press.

Some oil seeds of high oil content, such as copra, are difficult to express satisfactorily inbatch equipment by a singly pressing. In some places it is customary to break up the oilcake derived from the first pressing and subject it a second pressing with or withoutintervening moisture or heat treatment for the recovery of residual oil. Such practice, ofcourse, requires a double reduction of the seed and also yields an oil of inferior qualityfrom the second pressing. In American practice, the double pressing of oil seed isgenerally considered obsolete. Oil seeds that cannot be reduced to a low oil content by asingly pressing in hydraulic presses are preferably processed in continuous screw pressesor expellers.

CONTINUOUS PRESSINGContinuous expellers or screw presses are now used to the almost complete exclusion ofhydraulic presses for the mechanical extraction of soybeans and flaxseed in this countryand are of major importance for cottonseeds and peanuts. They are also used extensivelythroughout the world for the expression of copra, palm kernels, peanuts, cottonseed,flaxseed, and almost every variety of oil seed.

The continuous presses used on oil seeds in the United States are mostly high pressuremachines designed to effect oil recovery in one step. They are usually modified to suit aparticular material. In Europe various oil seeds are ordinarily handled by the same


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equipment, and it is common practice to press the seeds in two or even three stages atincreasingly higher pressure in each state. The low-pressure presses are also often usedfor "prepressing" prior to solvent extraction.

Continous presses effect a large saving in common labor over hydraulic systems and

completely eliminate the need for press cloth. They are adaptable to a wide variety ofmaterials, and in most cases they produce a much higher yield of oil. Their principaldisadvantages are that power requirements are relatively high, they require fairly well-skilled labor for both operation and maintenance and they are not well adapted tointermittent operation.

The first successful mechanical screw press, called an "expeller" (Model No. 1), wasmade by V.D. Anderson in 1900. I was soon used to express the oil from flaxseed andwhole cottonseed. About 1910 the Krupp Works was licensed to manufacture thesemachines in Germany, where they were used primarily as a for press unit ahead of

hydraulic presses. In the United States interest was gimarily in expressing as much oil aspossible from seed in the operation, so improvements were made resulting in an "RB"(roll bearing) expeller in 1926 and later the "duo" and "Super Duo" types. In 1933 a"screw press" was introduced by the Bench Oil Machinery Company. Today these twocompanies are the leading manufacturers of continuous screw press in this country.

The Anderson machines (expellers) utilize a vertical cage to express the most easilyremovable oil, followed by a horizontal cage for attainment of the high pressurenecessary for removal of most of the remaining oil. The French "screw presses" use onlya horizontal cage where pressure is gradually built up to a maximum. Another point o

morden tech oil extraction

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